YELLOW NUTSEDGE NUTLET PRODUCTION IN RESPONSE TO NUTLET PLANTING DEPTH

Transcription

1 YELLOW NUTSEDGE NUTLET PRODUCTION IN RESPONSE TO NUTLET PLANTING DEPTH Clinton C. Shock, Joey Ishida, and Erik Feibert Malheur Experiment Station Oregon State University Ontario, OR, 006 Introduction Yellow nutsedge has become a major problem weed in agricultural land in the Treasure Valley. Control of yellow nutsedge is difficult because reproduction is mainly by rhizomes and tubers (nutlets) and nutlet production is intense. Control of yellow nutsedge will partly rely on nutlet destruction by fumigation. Information on the depth at which most nutlets are produced and the maximum depth from which nutlets will emerge is essential for managing tillage and fumigation operations. This trial tested nutlet emergence, nutlet production, and depth of production for nutlets planted at different depths. Materials and Methods The experimental design was a randomized complete block with four replicates. The treatments were nine planting depths starting at inches and increasing in -inch increments. Each plot consisted of a 0-inch-diameter PVC pipe, 4 inches long. The pipes were cut lengthwise on two opposing sides. The pipes were then reassembled by taping the cut sides. The pipes were arranged in two parallel rows with 8 pipes in each row. The pipes were placed in a trench and the trench was filled so the top of the pipes were at ground level. The pipes were filled with soil and then drip-irrigated for 0 minutes. Each pipe was irrigated with one emitter with a gal/hour flow rate. On May 5, sprouted nutlets were collected from a field severely infested with yellow nutsedge. Two sprouted nutlets were planted at each pipe center, inches apart at the treatment depth. Planting holes were made with a soil probe to the correct depth. After planting, the pipes were irrigated for 5 minutes. Thereafter the pipes were irrigated weekly to maintain soil moisture to a -ft depth. A total of 94. inches of water was applied from May 5 to the last irrigation on October 0. On November 7, the pipes were dug up. Each pipe was opened along the precut sides and the soil column was cut vertically in -inch increments. The nutlets from each -inch depth increment were separated by washing and sieving. The nutlets from each -inch depth increment were counted and weighed. To calculate the average nutlet depth, the number of nutlets recovered from each soil depth increment were assigned the average depth of that soil depth treatment. The number of nutlets recovered from the 0- to -inch depth in a pipe was multiplied by, the number of nutlets recovered from the - to 4-inch depth was multiplied by, etc. Results and Discussion Large numbers of nutlets were produced in each pipe. There was no significant difference between planting depths in the total number, total weight, average weight, and average depth of the nutlets Malheur Experiment Station Annual Report 006. Oregon State University. Special Report 087. Pg 60-6

2 produced (Table ). On average, nutlets were produced at a.8-inch depth (Table ). Below the 4- to 6-inch depth, nutlet production decreased sharply with increasing depth (Fig. ). The results show that regardless of the depth of nutlet emergence, new nutlets form mostly in the upper 6 inches of soil. Table. Nutlet production and average depth of nutlets produced by yellow nutsedge plants originating from nutlets planted at nine depths. Malheur Experiment Station, Oregon State University, Ontario, OR. Planting depth Nutlets produced Total tuber weight Average tuber weight Average depth of tuber produced inches No./ ft oz/ft g inches, , , , , , , , , average, LSD (0.05) NS NS NS NS Malheur Experiment Station Annual Report 006. Oregon State University. Special Report 087. Pg 60-6

3 inch 4 inch 6 inch Depth, inch inch 0 inch inch inch 6 inch Nutlets/ft 8 inch Figure. Distribution of yellow nutsedge nutlets by depth from nutlets planted at nine depths. Malheur Experiment Station, Oregon State University, Ontario, OR. Malheur Experiment Station Annual Report 006. Oregon State University. Special Report 087. Pg 60-6

4 WEED CONTROL AND CROP RESPONSE WITH OPTION AND IMPACT HERBICIDES IN FURROW-IRRIGATED FIELD CORN Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Weed control is important in field corn production to reduce competition with the crop and to prevent the production of weed seed for future crops. Field trials were conducted to evaluate Option (foramsulfuron) herbicide applied with various adjuvants and to evaluate Impact (topramezone) in various combinations with other herbicides for weed control and crop tolerance in furrow-irrigated field corn. Option is a new postemergence sulfonylurea herbicide that controls annual and perennial grass and broadleaf weeds in field corn. Option contains a safener that is intended to enhance the ability of corn to recover from any yellowing or stunting sometimes associated with the application of sulfonylurea herbicides. Impact is also a new herbicide registered for use in corn that provides control of many broadleaf and grass weed species. Impact is a pigment synthesis inhibitor and causes bleaching of treated weeds. Materials and Methods Two trials were established to evaluate Option and Impact for weed control efficacy and crop safety in furrow-irrigated field corn. Croplan 44 field corn was planted with a John Deere model 7 Flexi Planter on May 4. Seed spacing was one seed every 7 inches. Plots were sidedressed with 58 lb nitrogen (N), 85 lb phosphorous, 6 lb sulfates, 6 lb zinc, lb boron, 5 lb manganese, and 00 lb elemental sulfur/acre on April 6. Plots were 7. by 0 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Herbicide treatments were applied with a CO- pressurized backpack sprayer. The sprayer was calibrated to deliver 0 gal/acre at 0 psi for the Option trial and 0 gal/acre at 0 psi for the Impact trial. Crop response and weed control were evaluated throughout the growing season. Corn yields were determined by harvesting ears from 6-ft sections of the center rows in each 4-row plot on November. The harvested ears were shelled and grain weight and percent moisture content were recorded. Grain yields were adjusted to percent moisture content. Data were analyzed using analysis of variance (ANOVA) and treatment means were separated using Fisher s protected least significant difference (LSD) at the 5 percent level (P = 0.05). Option was evaluated with various surfactant systems and in two combinations including Distinct. Impact was applied in combination with Aatrex, crop oil concentrate (COC) and percent urea ammonium nitrate (UAN) following preemergence applications of Dual II Magnum or Outlook. Impact treatments were compared to Callisto, Option, and Clarity treatments applied postemergence following preemergence applications of Dual II Magnum. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

5 Results and Discussion Option Combinations Option applied without a surfactant provided less control of pigweed species (Powell amaranth and redroot pigweed) and barnyardgrass than the other treatments (Table ). Common lambsquarters was the most difficult weed to control with Option, and Option without surfactant provided the least control. Option with COC for surfactant also had less common lambsquarters control than all other treatments containing surfactant. The addition of Distinct at either or 0. lb ai/acre to Option provided complete control of common lambsquarters. All treatments effectively controlled hairy nightshade, although nightshade populations were low. Kochia control was less when Option was applied without a surfactant, but was similar among treatments containing surfactant. Option must be applied with a surfactant to optimize weed control. The surfactant selected can affect control of difficult weeds such as common lambsquarters. Corn injury was affected by surfactant, with no surfactant or COC causing less injury than all treatments. Corn height was also reduced by all Option treatments except for those with COC or no surfactant. Corn yields were not different among treatments including the untreated control (Table ). Impact Combinations Dual II Magnum alone preemergence provided less control of pigweed species, common lambsquarters, hairy nightshade, and kochia than treatments containing a preemergence herbicide followed by postemergence treatments (Table ). Weed control was greater than 95 percent with preemergence and postemergence combinations and there were no differences among these treatments. Option postemergence caused significantly greater injury than all other treatments on June 8 (Table 4). Clarity also caused slightly higher injury than the other treatments. On July 5, injury was similar among preemergence and postemergence combinations. Corn height was reduced on June 8 by the Option treatment compared to all other treatments. Clarity reduced corn height compared to the untreated control, but height was similar to all other treatments except Option. On July 5 there were no differences in corn height among treatments. Corn yields were not different among treatments including the untreated control. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

6 Table. Weed control with Option herbicide applied with different surfactants and with Distinct in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed control Pigweed C. lambsquartershade Kochia grass H. night- Barnyard- Treatment Rate* Timing spp lb ai/acre pt/acre % v/v % Untreated Option + MSO + % N MP 99 a 96 ab a 00 a Option + MSO + % N MP 99 a 99 ab a 00 a Option + COC + % N % +.0 MP 00 a 84 c a 96 ab Option + MSO + AMS lb MP 99 a 97 ab a 98 a Option + % N MP 96 b 7 d b 89 b Option + Distinct + MSO + UAN % MP 00 a 00 a a 99 a Option + Distinct + MSO + UAN % MP 00 a 00 a a 00 a * Herbicide rates are in lb ai/acre. Additive rates are in pt/acre, percent v/v, or lb/acre. Treatments were applied mid-postemergence (MP) to corn at the V4 growth stage on June 0. Weed control was evaluated July 8. The untreated control was not included in the ANOVA for weed control. ANOVA was performed on arcsine square-root tranformed data. Non-transformed means are shown. Means followed by the same letter are not significantly different from each other at the P = 0.05 confidence level. Pigweed species were a mixture of Powell amaranth and redroot pigweed. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

7 Table. Injury, height, and yield with Option herbicide applied with different additives in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Field corn Injury Height Treatment Rate* Timing Yield lb ai/acre pt/acre % v/v % in bu/acre Untreated Option + MSO + % N MP Option + MSO + % N MP Option + COC + % N % +.0 MP Option + MSO + AMS lb MP Option + % N MP Option + Distinct + MSO + UAN % MP Option + Distinct + MSO + UAN % MP LSD (0.05) NS NS *Herbicide rates are in lb ai/acre. Additive rates are in pt/acre, percent v/v, or lb/acre. Treatments were applied mid-postemergence (MP) to corn at the V4 growth stage on June 0. The untreated control was not included in the ANOVA for percent injury. Corn was harvested November and yields were adjusted to percent moisture content. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

8 Table. Weed control with Impact herbicide in combinations with other herbicides applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Treatment Rate* Timing Pigweed spp Kochia Weed control C. lambs- H. nightshade quarters Barnyardgrass lb ai/acre % v/v % Untreated Dual II Magnum Dual II Magnum fb Impact + AAtrex + MSO + % N % +.5% MP Dual II Magnum fb Callisto + AAtrex + COC + % N % +.5% MP Dual II Magnum fb Clarity + NIS + % N.4 +.0% +.5% MP Dual II Magnum fb Option + MSO + % N % +.5% MP Outlook fb Impact + AAtrex + MSO + % N % +.5% MP LSD (0.05) 8 0 NS *Herbicide rates are in lb ai/acre. Additive rates are in percent v/v. Application timings were preemergence () on May 6 and mid-postemergence (MP) applied to corn at the V4 growth stage on June 8. Weed control was evaluated July 8. The untreated control was not included in the ANOVA for weed control. Pigweed species were a mixture of Powell amaranth and redroot pigweed. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

9 Table 4. Injury, height, and yield with Impact herbicide applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Field corn Injury Height Treatment Rate* Timing Yield lb ai/acre % v/v % in bu/acre Untreated Dual II Magnum Dual II Magnum fb Impact + AAtrex + MSO + % N % +.5% MP Dual II Magnum fb Callisto + AAtrex + COC + % N % +.5% MP Dual II Magnum fb Clarity + NIS + % N.4 +.0% +.5% MP Dual II Magnum fb Option + MSO + % N % +.5% MP Outlook fb Impact + AAtrex + MSO + % N % +.5% MP LSD (0.05).5 NS NS *Herbicide rates are in lb ai/acre. Additive rates are in percent v/v. Application timings were preemergence () on May 6 and mid-postemergence (MP) applied to corn at the V4 growth stage on June 8. The untreated control was not included in the ANOVA for percent injury. Corn was harvested November and yields were adjusted to percent moisture content. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

10 EVALUATIONS OF SPRING AND FALL HERBICIDES FOR PEPPERMINT Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Weed control in mint is essential in order to maintain high mint oil yields and quality. Reducing competition from weeds may also prolong the productive life of a mint stand. Chateau, a new herbicide, has recently been labeled for use in mint. This research was conducted to evaluate Chateau in combinations with other registered herbicides and to compare these mixtures to a standard herbicide treatment. Materials and Methods A trial was established near Nampa, Idaho to evaluate fall and spring herbicide applications to dormant mint for mint tolerance and weed control efficacy. Herbicides that were evaluated included a standard of Sinbar, Karmex, Stinger, and Prowl compared to Chateau in combinations with different herbicides including Sinbar, Karmex, Stinger, Treflan, and Gramoxone Extra. All herbicide treatments included a nonionic surfactant (Activator 90) at percent v/v. Fall applications were made December, 004 and spring applications were made February, 005. Herbicide treatments were arranged in a randomized block design with four replicates. Plots were 0 ft wide by 0 ft long. Herbicides were applied with a CO-pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Herbicide effects on weeds were determined by counting the number of each weed species present in each plot. Visual evaluations of mint injury could not be taken as mint was severely injured due to factors other than herbicide treatment. The trial was analyzed as a factorial design with two factors, herbicide treatment and application timing. Two treatments were included in the trial for comparison and were not included in the factorial analysis. Results and Discussion Application timing by herbicide interactions were significant for blue mustard and downy brome control, but this interaction may be due to variability in the weeds across the plots (Table ). There were significant differences among untreated plots, which demonstrated the variability in the weed distribution. Most treatments reduced blue mustard and downy brome densities. Treatments containing Gramoxone Extra eliminated downy brome. All treatments effectively controlled prickly lettuce. All treatments also reduced kochia density compared to the untreated check, with no significant differences among herbicide treatments. Pigweed densities were also reduced by all herbicide treatments compared to the untreated control. The combination of Chateau, Treflan, and Stinger had a higher density of pigweed than several other herbicide treatments including the combinations of Chateau, Treflan, and Gramoxone Extra, or Chateau, Sinbar, and Stinger. Overall, herbicides were effective in reducing both winter and summer annual weed densities. Control of these weeds was due almost entirely to the herbicides as very little mint was present to compete with the weeds or to prevent their germination. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -4

11 Table. Weed densities in response to fall and spring herbicide applications to dormant peppermint in Nampa, ID, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed densities Blue mustard Downy brome Prickly lettuce Kochia Pigweed Treatment* Rate Fall Spring Fall Spring lb ai/acre no/00 ft Untreated control Sinbar + Karmex + Stinger + Prowl + NIS % Sinbar + Karmex + Stinger + Chateau + NIS % Sinbar + Karmex + Chateau + Gramoxone Extra + NIS % Chateau + Treflan + Stinger + NIS % Chateau + Sinbar + Stinger + NIS % 0 0 Chateau + Karmex + Stinger + NIS % Chateau + Treflan + Gramoxone Extra + NIS % Chateau + Sinbar + Gramoxone Extra + NIS % Chateau + Karmex + Gramoxone Extra + NIS % Chateau + Gramoxone Extra + NIS % LSD (0.05) 4 47 Chateau + Stinger + NIS % Chateau + Stinger + NIS % *Fall applications were made December, 004. Spring treatments were made February, 005. Herbicide rates are lb ai/acre. NIS (nonionic surfactant, Activator 90) was applied at percent v/v. Blue mustard and downy brome densities were counted on April 8, 005. When significant herbicide by application timing effects were significant, data are presented by herbicide and application timing. When herbicide by application timing effects were not significant, densities were averaged over application timing. The treatments of Chateau plus Stinger were applied in the fall and again in the spring and are not included in the statistical analyses. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -4

12 Identification of Herbicides for Use in Native Forb Seed Production Clinton C. Shock, Joey Ishida, and Corey Ransom Malheur Experiment Station Oregon State University Ontario, OR Introduction Native forb seed is needed to restore the rangelands of the Intermountain West. Commercial seed production is necessary to provide the quantity of seed needed for restoration efforts. A major limitation to commercial production of native forb seed is the ability to control weeds within the seed crop. Weeds compete with crop plants, reducing establishment, vigor, and seed production. In addition, some weed seeds can contaminate the seed crop, reducing its value or introducing weeds to reclamation areas. Selective weed control products are needed for reliable native forb seed production at reasonable cost. A three-phase approach will be used to develop herbicide options for the production of native forb seed. Herbicides will be screened for plant tolerance, product rates will be tested, and field performance will be evaluated. The results from each phase will shape the design of the successive phases. Phase I, Initial Plant Tolerance to Herbicides In the greenhouse, each forb species will be screened for tolerance to herbicides. Herbicides for screening will be selected based on their potential for selectivity determined through literature reviews and our understanding of different modes of action and principles of selectivity. Forbs will be evaluated for their tolerance to herbicides applied either preemergence or postemergence. Phase II, Herbicide Rate Response Screen Once herbicides have been identified that have selectivity on the different forb species, a more detailed experiment in the greenhouse will examine the level of tolerance by testing the herbicides at rates of 0, ½,,, and 4 times the standard use rate. This "dose response" is critical to identify the level of safety that a herbicide has on the species it is being used on. Phase III, Field Testing Herbicides identified in greenhouse tests will be evaluated in the field to verify their safety on the forbs and their efficacy in controlling weeds under field conditions. Herbicides will be evaluated alone and when possible in combinations with each other to determine if weed control can be increased and crop safety maintained. The scale of field trials will depend on the number of candidate herbicides identified in the previous research phases and the availability of seed. Materials and Methods Two initial screening trials were initiated in 005 at the Malheur Experiment Station, one in the greenhouse and one in the field. Greenhouse Herbicide Screening Trial Sunshine all-purpose potting soil was mixed with silt loam from field A- at the Malheur Experiment Station and was used to fill 4 half trays (0.8 m by 0.8 m). On October and 4, seven native Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 5-8

13 species were planted in half trays at 50 seeds per tray with planting depth dependent upon the species (Table ). Seeds were equally spaced at 5 by 5 locations with seeds per location. Table. Forb species planted in the greenhouse herbicide screening trial at the Malheur Experiment Station, Ontario, OR, 005. Species Common name Depth, mm, (inches) Eriogonum umbellatum Sulfur buckwheat, (/8) Penstemon acuminatus Sand penstemon, (/8) Penstemon deustus Hotrock penstemon, (/8) Penstemon speciosus Royal or Sagebrush penstemon, (/8) Lomatium dissectum Fernleaf biscuitroot, (½) Lomatium triternatum Nineleaf desert parsley, (½) Lomatium grayi Gray's lomatium, (½) The trays were saturated October 7 and drained. The next day the trays were moved into a cooler set at C (4 F). The room was also humidified to reduce the need for frequent irrigation. The trays were saturated November 4 and returned to the cooler. On November 5 all trays were moved to the greenhouse head house for spraying. Four replicate trays of each of species received eight herbicide treatments (Table ). Products were applied in a spray chamber at 9. gal/acre of water with an 800E nozzle at 0 psi moving at mph. The air temperature was 5 F with 50 percent relative humidity. On November 6 each tray received /8 inch of water to incorporate the herbicide and the trays were returned to the cooler at 4 F. On November Lomatium triternatum, L. grayi, and Eriogonum umbellatum were moved to the greenhouse. On November 8, supplemental light was added to the greenhouse for 0 hours per day. On December the other forbs were moved to the greenhouse. Forbs were irrigated as needed and plant stands were counted twice a week. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 5-8

14 Field Herbicide Screening Trial The field was prepared in October 005 and bedded into 76-cm (0-inch) rows. On October, drip tape (T-Tape TSX ) was buried at 0.-m (-ft) depth and spaced.5 m (5 ft) apart. Two rows of forbs were planted 0.8 m (5 inches) to each side of the drip tape. Each species (Table ) was planted in a single row for a length of over m (400 ft). The drip tape was buried on alternating inter-row spaces. The flow rate for the drip tape was 0.4 gal/min/00 ft at 8 PSI with emitters spaced 0.4 m (6 inches) apart, resulting in a water application rate of inch/hour. The drip tape will be supplied with water filtered through sand media filters. Application durations can be controlled automatically and soil water content and water applied can be measured. None of the species had emerged by January 5, 006. The same herbicide products used in the greenhouse screening trial were applied at the same rates in the field on January 5. Five-ft-wide plots were assigned to the eight treatments in Table, perpendicular to the direction of the plant rows, with four replicates. A spray boom with three 800 E nozzles 0 inches apart covered the 5-ft plot width. Applications were based on 0 gal/acre, 0 psi, at.6 mph. The conditions were air temperature of 4 F, soil surface temperature 4 F, 0 percent cloud cover, and wind at mph from the east. Because the field was infested with blue mustard, common mallow, and wheat the field was sprayed with Roundup Ultra Max at.0 lb ai/acre on January 6. Table. Herbicides screened for forb tolerance at the Malheur Experiment Station, Ontario, OR, Treatment Product rate Rate Plant stands, % Lb ai/acre Lomatium grayi Dec Eriogonum umbellatum Jan 0 Lomatium dissectum Dec 0 Check none None Prefar 4.0 EC 5 qt/acre Kerb 50 WP lb/acre Treflan HFP 0.75 pt/acre / Prowl.8 SC.58 pt/acre ¾ Balan 60 DF lb/acre Outlook 6.0 EC 4 fl oz/acre / Lorox 50 DF lb/acre LSD (0.05) Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 5-8

15 Results and Discussion By late January reliable plant stands had been established for three species, Lomatium dissectum, L. grayi, and Eriogonum umbellatum, from the greenhouse screening trial. These plant stands showed significant differences between herbicide treatments (Table ). L. triternatum emerged slowly. In this preliminary screening trial, the forb species are tolerating different herbicides (Fig. ). Prefar, Balan, and Lorox look promising for L. grayi. Prowl has potential for Eriogonum umbellatum. Lorox, Prefar, and Kerb look promising for L. dissectum. These preliminary results should not be used as a basis for field treatments. LOGR* ERUM*** LODI* Plant stand, % Check Prefar Kerb Treflan Prowl Balan Outlook Lorox Product Figure. Plant stand of three forb species treated with seven herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR. LOGR is Lomatium grayi, ERUM is Eriogonum umbellatum, and LODI is Lomatium dissectum. * Treatment differences are significant at P = *** Treatment differences are significant at P = Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 5-8

16 EMERGENCE AND POSTEMERGENCE COMBINATIONS FOR WEED CONTROL IN ONION Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Because postemergence herbicides cannot be applied until onions have two true leaves, preemergence herbicide applications can be critical for limiting weed growth prior to when postemergence herbicides can be applied. Preemergence herbicides can control weeds as they germinate and reduce the size and number of weeds that are present until onions are large enough to tolerate postemergence herbicide applications. This research evaluated preemergence and postemergence herbicide combinations for weed control in onion. Materials and Methods A trial was conducted at the Malheur Experiment Station under furrow irrigation. On March, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at.7-inch spacing in double rows on - inch beds. Plots were 4 rows wide and 7 ft long and arranged in a split-plot design with 4 replicates. Lorsban was applied in a 6-inch band over each double row at.7 oz/,000 ft of row. Onions were sidedressed with 50 lb nitrogen, 50 lb phosphorus, 0 lb potassium, 0 lb sulfate, 8 lb zinc, 5 lb manganese, lb copper, and lb boron/acre on June 7. Registered insecticides and fungicides were applied for thrips and downy mildew control. Combinations of preemergence and postemergence herbicide applications were evaluated for weed control. Preemergence () treatments included no herbicide, Roundup (glyphosate), and Roundup plus Prowl (pendimethalin). Another treatment applied prior to the sequential postemergence treatments was Roundup applied preemergence followed by Prowl and Outlook (dimethenamid-p) applied postemergence to one-leaf onions. Sequential postemergence treatments included Buctril (bromoxynil) plus (oxyfluorfen) or Buctril plus Chateau (flumioxazin) applied to two- or four-leaf onions. All plots were treated with when onions had six leaves. Herbicide treatments were applied with a CO-pressurized backpack sprayer. Preemergence and one-leaf applications were applied at 0 gal/acre at 0 psi. All other postemergence applications were applied at 40 gal/acre at 0 psi. Preemergence treatments were applied on April. One-, two-, four-, and six-leaf applications were made on May 0, May, June 4, and June 6, respectively. All plots received Poast (sethoxydim) at 0.9 lbs ai/acre plus crop oil concentrate (COC) ( qt/acre) on May 4 to control grasses. Weed control and onion injury were evaluated throughout the season. Onions were harvested September -4 and graded by size on September 4-5. Treatments were arranged in a factorial design to allow the analysis of preemergence and postemergence treatment effects and interactions. Data were analyzed to determine significant effects and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Significance levels of main effects and interactions are included in Table. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-

17 Results and Discussion Rainfall activated preemergence treatments and postemergence treatments were effective because weeds were actively growing at the time herbicides were applied. Preemergence treatments did not cause onion injury (data not shown). On May 8, injury was similar among postemergence treatments (data not shown). On June, the treatment that included Buctril plus Chateau applied to four-leaf onions caused more injury ( percent) than treatments where Buctril plus Chateau was applied to two-leaf onions (0 percent) or where Buctril plus was applied sequentially (9 percent). On May, weed control was greatest with Roundup plus Prowl applied preemergence compared to the other preemergence treatments (Table ). Roundup preemergence followed by Prowl plus Outlook applied to one-leaf onions had greater pigweed, common lambsquarters, hairy nightshade, and barnyardgrass control than Roundup alone, but the two treatments provided similar kochia control. Significant preemergence herbicide by postemergence herbicide interactions were present for pigweed, hairy nightshade, and kochia control ratings taken September 8 (Table ). Depending on what preemergence treatments were applied, postemergence treatments responded differently in the control of these species. When no preemergence herbicides were applied, treatments containing Buctril plus Chateau provided greater control of pigweed, nightshade, and kochia compared to Buctril plus. When Roundup alone was applied preemergence, Buctril plus Chateau combinations provided greater pigweed control compared to Buctril plus. Also when Roundup alone was applied preemergence, Chateau plus Buctril applied to four-leaf onions controlled hairy nightshade and kochia better than Chateau plus Buctril applied to two-leaf onions and the Buctril plus treatment. When Roundup plus Prowl were applied preemergence or Roundup was applied preemergence followed by an application of Prowl plus Outlook to one-leaf onions, all postemergence herbicide combinations provided similar control of pigweed, nightshade, and kochia. Only preemergence herbicide treatments significantly affected common lambsquarters and barnyardgrass control on September 8 (Table 4). All preemergence treatments increased control of both species compared to no preemergence herbicide. Roundup alone had less control than Roundup plus Prowl preemergence or Roundup preemergence followed by Prowl plus Outlook applied to one-leaf onions. Treatments containing Prowl had the highest common lambsquarters and barnyardgrass control. Onion yields were significantly different among preemergence treatments (Table 5). Roundup preemergence increased medium, jumbo, total, and marketable yields compared to no preemergence treatment, but yields were significantly less than with Roundup plus Prowl preemergence or Roundup preemergence followed by Prowl plus Outlook at one-leaf onions. Roundup plus Prowl preemergence had fewer medium onions and greater jumbo, colossal, total, and marketable yields compared to Roundup preemergence followed by Prowl plus Outlook applied to one-leaf onions. It is possible that this yield increase resulted from the prevention of early weed competition. This research demonstrates that the effectiveness of postemergence herbicide programs is strongly related to early season weed control. Although in several instances weed control was similar between different treatments at the conclusion of the season, yields were reduced in treatments where weeds were allowed to compete early. The use of an effective preemergence herbicide may provide the best opportunity for effectively controlling weeds with postemergence herbicides and for maximizing onion yield. An effective preemergence herbicide could also potentially allow a producer to use lower rates of postemergence herbicides to achieve acceptable weed control. This research also demonstrated that Buctril plus Chateau applied to four-leaf onions can provide increased weed control under certain conditions, but application of Buctril plus Chateau at that timing also caused Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-

18 greater injury than the other treatments. The level of injury observed would likely not be acceptable in commercial onion production. Table. Significance of preemergence and postemergence treatment main effects and the preemergence by postemergence interactions for onion injury and yield and weed control evaluation data, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Onion Weed control Common Hairy Effects Injury 5-8 Injury 6- Total yield Pigweed lambsquarters nightshade Kochia Barnyardgrass probability (F)* Preemergence Postemergence X POST *Main effects or interactions with probabilities equal to or less than 0.05 are considered significant. Table. Weed control in onion provided by preemergence and early postemergence herbicide applications prior to spraying sequential postemergence treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed control Treatment Rate * Timing Pigweed Common Hairy Barnyard Kochia lambsquarters nightshade grass lb ai or ae/acre % None Roundup Roundup + Prowl Roundup Prowl + Outlook leaf LSD (0.05) *Roundup rates are in lb ae/acre and all other herbicides are lb ai/acre. Preemergence () treatments were applied on April and one-leaf (-leaf) on May 0. Pigweed is a combination of redroot pigweed and Powell amaranth. Weed control was evaluated on May, prior to the beginning of sequential postemergence herbicide applications. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-

19 Table. Weed control in onion with preemergence and postemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed control Treatment Rate * Timing Pigweed Hairy nightshade None Buctril+ Chateau None Buctril + Chateau None Roundup Buctril + Chateau Roundup Buctril + Chateau Roundup Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Roundup Prowl + Outlook Buctril + Chateau Roundup Prowl + Outlook Buctril + Chateau Roundup Prowl + Outlook Kochia lb ai or ae/acre Leaf % leaf 6-leaf 6-leaf 6-leaf 6-leaf 6-leaf 6-leaf 6-leaf 6-leaf -leaf 6-leaf -leaf 6-leaf -leaf 6-leaf LSD (0.05) *Roundup rates are in lb ae/acre and all other herbicides are in lb ai/acre. Preemergence () treatments were applied on April, one-leaf (-leaf) on May 0, two-leaf () on May, four-leaf () on June 4, and six-leaf (6-leaf) on June 6. Pigweed is a combination of redroot pigweed and Powell amaranth. Weed control was evaluated on September 8. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-

20 Table 4. Weed control in onion provided by preemergence herbicide applications averaged over postemergence treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Treatment Rate * Timing Common lambsquarters Weed control Barnyard grass lb ai or ae/acre % None Roundup Roundup + Prowl Roundup Prowl + Outlook leaf LSD (0.05) *Roundup rates are in lb ae/acre and all other herbicides are in lb ai/acre. Preemergence () treatments were applied on April and one-leaf (-leaf) on May 0. Weed control was evaluated on September 8 and are averaged over postemergence herbicide treatments. Table 5. Onion yield as influenced by preemergence herbicide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. None Onion yield Treatment Rate* Timing Small Medium Jumbo Colossal Super- Colossal lb ai or ae/acre Total cwt/acre Marketable Roundup Roundup + Prowl Roundup Prowl + Outlook LSD (0.05) leaf NS 5 6 *Roundup rates are in lb ae/acre all other herbicides are in lb ai/acre. Preemergence () treatments were applied on April and one-leaf (-leaf) on May 0. Onions were harvested September and 4. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-

21 SOIL-ACTIVE HERBICIDE APPLICATIONS FOR WEED CONTROL IN ONION Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction The use of soil-active herbicides applied preemergence or postemergence can reduce the number and size of weeds in onions. Evaluating the best time to apply soil-active herbicides and the most effective combinations may help onion producers achieve greater weed control. In addition, the combination of postemergence fungicides with postemergence herbicides has the potential to increase onion injury. Testing these types of combinations can reduce the probability of large scale problems when growers begin using new products. This trial was conducted to evaluate the effect of different application timings of Prowl H O (pendimethalin) and Outlook (dimethenamid-p) on onion injury and weed control and to evaluate different application timings for Pristine (pyraclostrobin + boscalid), a new fungicide, in combination with postemergence herbicides. Materials and Methods A trial was conducted at the Malheur Experiment Station under furrow irrigation. On March, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at.7-inch spacing in double rows on - inch beds. Plots were 4 rows wide and 7 ft long and arranged in a randomized complete block design with 4 replicates. Lorsban was applied in a 6-inch band over each double row at.7 oz/,000 ft of row. Onions were sidedressed with 50 lb nitrogen, 50 lb phosphorus, 0 lb potassium, 0 lb sulfate, 8 lb zinc, 5 lb manganese, lb copper, and lb boron/acre on June 7. Registered insecticides and fungicides were applied for thrips and downy mildew control. All plots were treated with Roundup (glyphosate) preemergence. Outlook was applied preemergence () alone and in combination with Prowl H O or in combination with Prowl H O at flag-leaf onions or following preemergence applications of Prowl H O. Postemergence treatments consisted of two sequential postemergence applications of Buctril (bromoxynil) plus (oxyfluorfen) and a final postemergence application of. Pristine was applied in combination with Buctril plus to four-leaf onions or in combination with to six-leaf onions or at both application timings. Treatments were applied with a CO -pressurized backpack sprayer. Preemergence and flag-leaf applications were applied at 0 gal/acre at 0 psi. All other postemergence applications were applied at 40 gal/acre at 0 psi. Preemergence treatments were applied on April. Applications to flag-, two-, four-, and six-leaf onions were made on April 6, May, June 4, and June 5, respectively. All plots received Poast (sethoxydim) at 0.9 lbs ai/acre plus crop oil concentrate (COC) ( qt/acre) on May 4 to control grasses. Weed control and onion injury were evaluated throughout the season. Onions were harvested September -4 and were graded by size on September 4-5. Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -5

22 Results and Discussion Rainfall activated preemergence treatments and postemergence treatments were effective because weeds were actively growing at the time that the herbicides were applied. Outlook applied alone preemergence provided less control of common lambsquarters, hairy nightshade, kochia, and barnyardgrass compared to other treatments (Table ). Prowl H O applied either preemergence or to flag-leaf onions was more effective than Outlook alone and there was no increase in weed control from additions of Outlook to treatments that contained Prowl H O. However, in past trials and in commercial fields with yellow nutsedge, Outlook has provided definite benefits. On May 8, in all but one instance, treatments with Outlook applied to two-leaf onions in combination with Buctril and had greater injury than treatments that did not combine Outlook with Buctril and (Table ). There were fewer differences in injury among treatments on June. By July, there was no visible onion injury for any treatment (data not shown). Because weed control was less, onions grown with Outlook alone preemergence had lower total and marketable yields compared to all other treatments except Prowl H O applied to flag-leaf onions followed by Outook plus Buctril and applied to two-leaf onions (Table ). Even though treatments where Outlook was combined with Buctril and applied postemergence caused increased onion injury, onion yields were not reduced. Conditions were ideal in 005 for soil-applied herbicides to control weeds. In years where conditions are drier, we would expect more differences among these types of herbicide treatments. The addition of Pristine to postemergence herbicide applications did not increase onion injury or affect weed control. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -5

23 Table. Weed control in onion in response to different application timings of Outlook, Prowl H O, and Pristine, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Treatment Rate* Timing Pigweed Common lambsquarters Weed control Hairy Kochia Barnyardgrass nightshade lb ai or ae/acre Leaf % Untreated Roundup + Outlook Roundup Prowl H 0 Roundup Prowl H 0 + Outlook Roundup Prowl H 0 + Outlook Roundup + Prowl H 0 + Outlook Roundup Prowl H 0 + Outlook + Pristine Roundup Prowl H 0 + Outlook + Pristine Roundup Prowl H 0 + Outlook + Pristine + Pristine Roundup + Prowl H 0 + Outlook oz oz oz oz leaf flag 6-leaf flag 6-leaf flag 6-leaf 6-leaf flag 6-leaf flag 6-leaf flag 6-leaf 6-leaf LSD (0.05) NS *Roundup rates are in lb ae/acre and all other herbicides are lb ai/acre. Preemergence () treatments were applied on April, flag-leaf (flag) on April 6, two-leaf () on May, four-leaf () on June 4, and sixleaf (6-leaf) on June 5. Weed control was evaluated on September 8. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -5

24 Table. Onion injury and yield in response to different application timings of Outlook, Prowl H O, and Pristine, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Onion injury Onion yield Treatment Rate* Timing Total Marketable lb ai or ae/acre Leaf % cwt/acre Untreated Roundup + Outlook leaf Roundup Prowl H Flag 6-leaf Roundup Prowl H 0 + Outlook Roundup Prowl H 0 + Outlook Roundup + Prowl H 0 + Outlook Flag 6-leaf Flag 6-leaf 6-leaf Roundup Prowl H 0 + Outlook + Pristine oz Flag 6-leaf Roundup Prowl H 0 + Outlook + Pristine oz Flag 6-leaf Roundup Prowl H 0 + Outlook + Pristine + Pristine oz oz Flag 6-leaf Roundup + Prowl H 0 + Outlook leaf LSD (0.05) *Roundup rates are in lb ae/acre and all other herbicides are lb ai/acre. Preemergence () treatments were applied on April, flag-leaf (flag) on April 6, two-leaf () on May, four-leaf () on June 4, and sixleaf (6-leaf) on June 5. Onions were harvested on September and 4. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg -5

25 COMPARISON OF GOAL XL AND GOALTENDER FOR CROP INJURY AND WEED CONTROL IN ONION Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction tender is a new formulation of oxyfluorfen, the same active ingredient in XL. tender is currently registered for use in onions. tender is a water-based formulation and does not use solvents as a carrier for the herbicide as does XL. Because solvents can remove leaf wax from plant leaves, it is possible that by using a water-based formulation of oxyfluorfen, onion injury can be reduced, or oxyfluorfen can be applied to smaller onions. The research reported here evaluated XL and tender applied at two onion growth stages for onion tolerance and weed control efficacy. Materials and Methods A trial was conducted at the Malheur Experiment Station under furrow irrigation. On March, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at.7-inch spacing in double rows on - inch beds. Plots were 4 rows wide and 7 ft long and arranged in a randomized complete block design with 4 replicates. Lorsban was applied in a 6-inch band over each double row at.7 oz/,000 ft of row. Onions were sidedressed with 50 lb nitrogen, 50 lb phosphorus, 0 lb potassium, 0 lb sulfate, 8 lb zinc, 5 lb manganese, lb copper, and lb boron/acre on June 7. Registered insecticides and fungicides were applied for thrips and downy mildew control. All plots were treated with Roundup (glyphosate) at 0.75 lb ae/acre preemergence on April. XL or tender were applied at different rates to one- or two-leaf onions. Herbicide treatments were applied with a CO -pressurized backpack sprayer. Preemergence Roundup was applied at 0 gal/acre at 0 psi. Postemergence treatments were applied at 40 gal/acre at 0 psi. Applications were made to one-leaf onions on May 7 and to two-leaf onions on May. All plots received Poast (sethoxydim) at 0.9 lbs ai/acre plus crop oil concentrate (COC) ( qt/acre) on May 4 to control grasses. Weed control and onion injury were evaluated through June. Because single postemergence herbicide applications did not effectively control weeds, the trial was concluded on June and onion yields were not taken. Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Results and Discussion Onion injury was not different for XL or tender on May 0 or May 7 (Table ). Injury on May 7 was severe, ranging from 5 to 4 percent. On May 4, injury with tender applied to one-leaf onions was less with 0.5 lb ai/acre compared to 0.88 lb ai/acre. XL applied to oneleaf onions caused injury similar to both rates of tender. At the same application rates, XL caused greater injury than tender when applied to two-leaf onions. On May 8, onion injury among treatments was not different, and on June all treatments applied to two-leaf onions Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-8

26 exhibited greater injury than treatments applied to one-leaf onions. Onion injury is inversely related to the time that has elapsed since the last postemergence herbicide application. Herbicide applications to one-leaf onions provided significantly greater control of pigweed, common lambsquarters, and hairy nightshade compared to herbicide application to two-leaf onions (Table ). This is because the weeds were very small when the one-leaf applications were made and grew significantly larger by the time the two-leaf applications were made. XL and tender applied to one-leaf onions provided similar control of pigweed and hairy nightshade. However, on May 4 and June XL provided greater control of common lambsquarters. For application to two-leaf onions, increasing the rate of either XL or tender increased the control of all weed species. In all cases, when applied at the same rate, XL provided greater control of pigweed, common lambsquarters, and hairy nightshade compared to tender. Effective weed control was not possible with a single postemergence herbicide application. Conducting a similar trial with additional sequential postemergence treatments may produce a different outcome. While there was a trend for less onion injury by using tender, there were also reductions in the level of weed control. There was little advantage to using tender early to reduce onion injury in this trial. However, under different environmental conditions, a non-solvent-based herbicide may provide additional crop safety. Further testing is needed to determine how tender may fit into a weed management program in bulb onion. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-8

27 Table. Onion injury in response to rates and timings of applications of XL, and tender, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Onion injury Treatment* Rate Timing lb ai/acre Leaf Untreated tender 0.5 -leaf tender leaf XL 0.5 -leaf tender tender XL XL LSD (0.05) NS NS 4.7 NS 4 *All plots were treated with Roundup (0.75 lb ae/acre) preemergence on April. Treatments were applied to one-leaf (-leaf) onions on May 7 and to two-leaf () onions on May. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-8

28 Table. Weed control in onion in response to rates and timings of applications of XL, and tender, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Pigweed Weed control Common lambsquarters Hairy nightshade Treatment * Rate Timing lb ai/acre Leaf Untreated tender 0.5 -leaf tender leaf XL 0.5 -leaf tender tender XL XL LSD (0.05) *All plots were treated with Roundup (0.75 lb ae/acre) preemergence on April. Treatments were applied to one-leaf (-leaf) onions on May 7 and to two-leaf () onions on May. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 6-8

29 DEVELOPMENT OF NEW HERBICIDE OPTIONS FOR WEED CONTROL IN POTATO PRODUCTION Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Weed control in potatoes is essential for production of high yielding marketable tubers. Herbicide options in potato production are limited. Chateau (previously called Valor ) has demonstrated promise for use in potato in previous research. Chateau represents a mode of action that is not currently used in potatoes and offers excellent hairy nightshade control. A trial was conducted to evaluate two-way tank mixture with and without the addition of Chateau to determine if it can be added to increase weed control, especially hairy nightshade. Materials and Methods A trial was conducted at the Malheur Experiment Station to evaluate Chateau additions to two-way tank mixtures for enhanced weed control efficacy. The ground was ripped in the fall and because of fall rains hilling was done in the spring on March 8. Potatoes were planted April, 005 in an Owyhee silt loam soil with ph 7.6,.7 percent organic matter content, and a cation exchange capacity of 9. Russet Burbank seed pieces were planted every 9 inches in 6-inch-wide rows. Seed pieces were treated with Tops-MZ plus Gaucho. Experimental plots were 4 rows wide and 0 ft long. Plots were sidedressed with 74 lb nitrogen (N), 94 lb phosphorus (P), 45 lb potassium (K), 8 lb sulfate, 7 lb elemental sulfur (S), 5 lb zinc (Zn), 6 lb manganese (Mn), and lb boron (B)/acre on April 9 and rehilled on May. Preemergence herbicides were applied with a CO -pressurized backpack sprayer delivering 0 gal/acre at 0 psi and incorporated with approximately 0.5 inch of sprinkler irrigation on May. On July 5, 0 lb N/acre was applied through the sprinkler. Aerial fungicide applications included Ridomil Gold and Bravo at.5 pt/acre on June, Endura at 0 oz/acre plus Dithane at lb/acre plus Folo Spray on June 8, Dithane at lb/acre plus liquid S at 6 lb/acre on June 8, Bravo at.5 pt/acre on July 0, Dithane at lb/acre plus Tanos at 8 oz/acre on July 8, and Bravo at.5 pt/acre on September 6. On August 0, 6 lb S/acre was applied to prevent two-spotted spider mite infestation. Visual potato injury and weed control were evaluated throughout the growing season. Tubers were harvested from the center two rows of each plot on September 7. Potatoes were graded for yield and size on September 8 and 9. Results and Discussion Rainfall at the time of potato emergence resulted in significant injury from several of the herbicide combinations. In all cases, three-way tank mixtures containing Chateau had greater injury on May than the corresponding two-way tank mixtures without Chateau (Table ). Prowl plus Outlook also had higher injury compared to all the other standard two-way tank mixtures. For some reason the three-way combination of Prowl, Sencor, and Chateau had less injury than all other treatments containing Chateau. Injury decreased with time, but on June 8, relative injury associated with Chateau treatments was similar to the earlier evaluation. The three-way combination of Prowl, Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 94-97

30 Sencor, and Chateau did not differ in injury from the two-way combination of Prowl and Sencor. By July, no injury was visible with any herbicide treatment (data not shown). All treatments controlled pigweed species (redroot pigweed and Powell amaranth) greater than 95 percent except for Dual Magnum plus Prowl (Table ). Common lambsquarters control was lower with Dual Magnum plus Prowl compared to the other treatments. Outlook combined with Chateau provided less lambsquarters control than Prowl plus Sencor or the three-way tank mixture of Prowl, Outlook, and Chateau. Prowl plus Sencor provided the least hairy nightshade control of all the herbicide treatments. Adding Chateau to Prowl plus Sencor significantly improved hairy nightshade control, but control was still less than with the other combinations. Treatments providing greater than 90 percent control of hairy nightshade contained either Outlook or Chateau. All treatments controlled kochia and barnyardgrass and percent, respectively. Potato yields were similar among all treatments with the exception that Dual Magnum plus Sencor had greater tuber yields in the 6- to -oz, greater than -oz, total, marketable, and total U.S. No. s categories than Prowl plus Sencor. Reduced yields with the Prowl plus Sencor tank mixture could be related to the poor hairy nightshade control. Yields did not appear to be related to the crop injury observed early in the season. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 94-97

31 Table. Comparison of standard - and -way tank mixtures with Chateau for potato crop injury and weed control, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Potato injury Treatment* Rate Pigweed Common lambsquarters Weed control Hairy nightshade Kochia Barnyard grass lb ai/acre % Untreated check Dual Magnum + Sencor a 99 ab 84 bc 00 a 00 a Prowl + Sencor a 00 a 49 d 00 a 00 a Dual Magnum + Prowl b 8 c 80 c 00 a 99 a Prowl + Outlook a 97 ab 96 abc 97 a 99 a Dual Magnum + Sencor + Chateau ab 99 ab 9 abc 00 a 97 a Sencor + Prowl + Chateau a 99 ab 8 c 00 a 99 a Dual Magnum + Prowl + Chateau a 9 abc 9 abc 00 a 98 a Prowl + Outlook + Chateau a 00 a 99 a 99 a 98 a Outlook + Chateau a 9 bc 98 ab 00 a 95 a LSD (P = 0.05) *Herbicide treatments were applied preemergence on May, 005. Weed control evaluations were taken September. Weed control data were arcsine transformed prior to analysis. Nontransformed means are presented. Means followed by the same letter are not significantly different at the P = 0.05 confidence level. Pigweed species were a combination of Powell amaranth and redroot pigweed. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 94-97

32 Table. Effect of standard - and -way tank mixtures with Chateau on potato yield and quality, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. U.S. No. Potato yield Treatment* Rate 4-6 oz 6- oz > oz Total Percent Total No. Total marketable Total yield lb ai/acre cwt/acre % cwt/acre Untreated check Dual Magnum + Sencor Prowl + Sencor Dual Magnum + Prowl Prowl + Outlook Dual Magnum + Sencor + Chateau Sencor + Prowl + Chateau Dual Magnum + Prowl + Chateau Prowl + Outlook + Chateau Outlook + Chateau LSD (0.05) *Herbicide treatments were applied preemergence on May, 005. Potatoes were harvested September 7. Total marketable yield = total U.S. No. s + total U.S. No. s. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 94-97

33 CONTROL OF PERENNIAL PEPPERWEED AND RUSSIAN KNAPWEED WITH HABITAT AND PLATEAU HERBICIDES Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Russian knapweed and perennial pepperweed are deep-rooted perennial weeds that are troublesome across the Western United States. Both species are often associated with riparian areas and research has illustrated that seed germination of both species is suited to riparian and meadow environments (Larson and Kiemnec 005). Tillage has little effect on long-term control of these weeds. Perennial pepperweed has shown greater sensitivity to chlorsulfuron than to,4-d or glyphosate (Young et al. 998). Combinations of seeding competitive grass species following applications of picloram or clopyralid effectively reduced Russian knapweed stands (Bottoms and Whitson 998). Habitat (imazapyr) and Plateau (imazapic) are ALS-inhibiting herbicides that are active activity on a variety of perennial species. Habitat was recently registered for use in aquatic and riparian settings, making it a candidate for controlling perennial pepperweed and Russian knapweed. Materials and Methods In 004, four trials were established to evaluate Habitat and Plateau for control of Russian knapweed and perennial pepperweed. Russian knapweed trials were established adjacent to Succor Creek, south of Adrian, Oregon. One perennial pepperweed trial was established adjacent to the Snake River in Ontario, Oregon and the other near the Malheur River, west of Vale, Oregon. Treatments were Habitat (0.06, 0.094, 0.5, 0.87,, 0.75, and 0.5 lb ai/acre) and Plateau (0.5 and 0.87 lb ai/acre). Treatments were arranged in a randomized block design with four replicates. One Russian knapweed trial was treated August, 004 when Russian knapweed was starting to senesce. The second trial was treated November, 004. The first perennial pepperweed trial was treated June 4, 004 while the pepperweed was in full bloom. The second trial was sprayed December 4, 004. All treatments included methylated seed oil (MSO) at.5 percent v/v. Herbicide treatments were applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Perennial pepperweed trials were evaluated June 0, 005 and Russian knapweed trials July 8, 005. Results and Discussion With summer herbicide applications, Russian knapweed control the following spring was greater than 90 percent only with 0.5 lb ai/acre of Habitat and control decreased with rates below lb ai/acre (Table ). Plateau rates below 0.5 lb ai/acre and Habitat at 0.5 and 0.87 lb ai/acre provided percent or less Russian knapweed control. When herbicide treatments were applied to dormant Russian knapweed in November, Habitat rates above lb ai/acre provided percent control. Russian knapweed control declined as Habitat rates were reduced, to a low of 54 percent with lb ai/acre. Plateau at 0.5 and 0.87 lb ai/acre provided 67 and 87 percent control, respectively. Both Habitat and Plateau were more active on Russian knapweed when applied in the fall as compared to the summer. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 98-0

34 For perennial pepperweed, summer application of Habitat and Plateau resulted in 95 percent or greater control the following June regardless of herbicide rate. When applied in December, perennial pepperweed control the following summer was 94 percent with Habitat at 0.5 lb ai/acre and declined at Habitat rates of lb ai/acre or lower. Plateau provided 64 and 7 percent control at the respective rates of 0.5 and 0.87 lb ai/acre. Young et al. (998) did not see a difference in perennial pepperweed control with different Telar application timings, but that could be attributed to the fact that only one rate was evaluated. Our research demonstrates that Habitat and Plateau are active on Russian knapweed and perennial pepperweed and that application timing in the summer is essential for effective control of these herbicides on these weed species. Selecting the proper application timing may allow weed control with lower herbicide rates, allowing establishment of/or selectivity for desirable plant species. References Bottoms, R. M., and T. D. Whitson A systems approach for the management of Russian knapweed (Centaurea repens). Weed Technol. :6 66. Larson, L., and G. Kiemnec Germination of two noxious range weeds under water and salt stresses with variable light regimes. Weed Technol. 9: Young, J. A., D. E. Palmquist, and R. R. Blank The ecology and control of perennial pepperweed (Lepidium latifolium L.). Weed Technol. : Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 98-0

35 Table. Perennial pepperweed and Russain knapweed control with summer or fall applications of Habitat and Plateau herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed control* Perennial pepperweed Russian knapweed Treatment Rate Summer Fall Summer Fall lb ai/acre % v/v % Untreated Habitat + MSO % Habitat + MSO % Habitat + MSO % Habitat + MSO % Habitat + MSO +.5% Habitat + MSO % Habitat + MSO % Plateau + MSO % Plateau + MSO % LSD (0.05) *Perennial pepperweed control was evaluated June 0 and Russian knapweed control on July 8, 005. Treatments were applied June 4, 004 when perennial pepperweed was in full bloom. The research site was near the Snake River in Ontario, Oregon. Treatments were applied December 4, 004. The research site was near the Malheur River, west of Vale, Oregon. Treatments were applied August, 004 as Russian knapweed plants were beginning to senesce. The research site was near Succor Creek, south of Adrian, Oregon. Treatments were applied November, 004. The research site was near Succor Creek, south of Adrian, Oregon. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 98-0

36 KOCHIA CONTROL WITH EMERGENCE NORTRON IN STANDARD AND MICRO-RATE HERBICIDE PROGRAMS IN SUGAR BEET Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction The distribution of kochia resistant to UpBeet (triflusulfuron) herbicide and other acetolactate synthase (ALS) inhibitors (i.e., sulfonylureas, imidazolinones, and triazolopyrimidines) has increased in recent years and poses a serious problem in sugar beet production, as none of the currently registered postemergence herbicides effectively control ALS-resistant kochia. In this trial, Nortron (ethofumesate) was evaluated for preemergence control of kochia in sugar beet. Nortron is a soilactive herbicide used preemergence or early postemergence to control annual grasses and broadleaf weeds. Materials and Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 6, 005. Sugar beets (Hilleshog 'PM-90') were planted in -inch rows at a -inch seed spacing. On April 7, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May and. Plots were sidedressed on June 8 with 50 lb nitrogen (urea), 50 lb phosphate (P O 5 ), 0 lb potash (K O), 0 lb sulfates (SO 4 ), 5 lb manganese (Mn), 8 lb zinc (Zn), lb copper (Cu), and -lb/acre boron (B). All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On April 8, Temik 5G (4 lb prod/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 4, Dithane ( lb prod/acre) plus sulfur (6 lb/acre) were applied June 8, sulfur (6 lb/acre) was applied August 0, and Gem (7 fl oz/acre) was applied August 5. All fungicide treatments were applied by air. Herbicide treatments were broadcastapplied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were 4 rows wide and 7 ft long and treatments were arranged in a randomized complete block design with 4 replicates. The treatments in this trial consisted of standard and micro-rate postemergence weed control programs applied with or without a preemergence application of Nortron at 6, 4, or oz ai/acre with and without postemergence UpBeet. For the micro-rate treatment without UpBeet, Nortron was also applied preemergence at 48 oz ai/acre. UpBeet was omitted from selected treatments to simulate ALS resistance and to better evaluate preemergence Nortron efficacy on kochia. Nortron was applied preemergence on April. The standard rate program included three applications, with the first applied to full cotyledon sugar beets on April, the second to two- to four-leaf sugar beets on May, and the third application to four- to eight-leaf sugar beets on May. Progress (ethofumesate + phenmedipham + desmedipham) was applied at 4.0, 5.4, and 6.7 oz ai/acre in the first, second, and third applications, respectively. UpBeet was applied at oz ai/acre in all three applications (excluding treatments where UpBeet was omitted). Stinger (clopyralid) was applied in the second and third applications at.5 oz ai/acre. The micro-rate program consisted of four applications with the first applied to cotyledon sugar beets on April, the second to cotyledon to two-leaf sugar beets on April 9, the third application was applied to two- to six-leaf sugar beets on Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

37 May 7, and the fourth to four- to eight-leaf sugar beets on May. In the micro-rate program, Progress was applied at. oz ai/acre in the first two applications and at.0 oz ai/acre in the last two applications. All four micro-rate applications included UpBeet at 0.08 oz ai/acre (excluding treatments where UpBeet was omitted), Stinger at 0.5 oz ai/acre, and a methylated seed oil (MSO) at.5 percent v/v. Sugar beet injury was evaluated May and June 7 and weed control was evaluated July 7 and September. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Syngenta Seeds Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion Postemergence herbicides were very effective, likely because of frequent rainfall during April and May. All herbicide treatments effectively controlled common lambsquarters, hairy nightshade, and barnyardgrass (Table ). On July 6 and August 7, the micro-rate without Upbeet provided the least kochia control of all the treatments. On August 7, Powell amaranth and redroot pigweed control was less with the micro-rate without Upbeet compared to all other treatments. Removing Upbeet from the standard postemergence treatment did not significantly affect kochia control compared to all other standard rate treatments. When the micro-rate was applied following Nortron (4 pt/acre) the removal of Upbeet reduced kochia control compared to the same treatment with Upbeet included. Sugar beet yields were related to the level of kochia control provided by each herbicide treatment (Fig. ). The micro-rate without Upbeet had the lowest sugar beet root yield and estimated recoverable sugar of any herbicide treatment (Table ). When Nortron was applied preemergence at.0 or 4.0 pt/acre, removing Upbeet from postemergence micro-rate applications reduced yield compared to the same treatments with Upbeet. Estimated recoverable sugar was also reduced when Upbeet was removed from the micro-rate following preemergence Nortron (.0 pt/acre). In locations where Upbeet-resistant kochia is present, the use of preemergence Nortron can be used to provide additional control of ALS kochia that are not susceptible to Upbeet. When ALS-resistant kochia are present, it is recommended that producers apply standard herbicide rates as they are more effective than micro-rates for controlling kochia. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

38 60 50 y = x R = 0.85, P < Sugar beet yield (ton/acre) Kochia control (%) Figure. Relationship of sugar beet yield and visual kochia control ratings, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

39 Table. Kochia control with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Weed control Pigweed Lambsquarters nightshade grass Hairy Barnyard- Kochia spp. Treatment* Rate Timing oz ai/acre & % v/v % Untreated control Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Micro-Rate Program Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron fb Standard with Upbeet Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet % v/v % v/v , 5,6,4,7,4,7,4,7,4,7,4,7,4,7,,5,6,,5,6,,5,6,,5,6,,5,6,,5, Standard w/out UpBeet ---,4, Micro w/out UpBeet ---,,5, Nortron fb Micro w/out UpBeet ,,5, LSD ( 0.05) NS NS NS *fb = followed by. Application timings were () April preemergence, () April to cotyledon beets, () April 9 to full cotyledon beets, (4) May to - to beets, (5) May 7 to - to 6-leaf beets, (6) May to 4- to 8-leaf beets, and (7) May to 4- to 8- leaf beets. Pigweed species included Powell amaranth and redroot pigweed. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

40 Table. Sugar beet injury and yield with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 005. Sugar beet Injury Yield Treatment* Rate Timing Root yield Sucrose Extraction ERS oz ai/acre and % v/v % ton/acre % lbs/acre Untreated control ,076 Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Micro-Rate Program Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard w/out UpBeet % v/v % v/v , 5, , ,8,4, ,,4, ,7,4, ,889,4, ,74 Nortron fb Standard w/out UpBeet ,4, ,49 Nortron fb Standard w/out UpBeet.0 ---,4, ,560 Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet ,,5,6,,5,6,,5,6,,5,6,,5,6,,5, , , , , , ,0 Standard w/out UpBeet ---,4, , Micro w/out UpBeet ---,,5, ,58 Nortron fb Micro w/out UpBeet ,,5, ,6 LSD (0.05) NS 5.4 NS 0.7,666 *fb = followed by. Application timings were () April preemergence, () April to cotyledon beets, () April 9 to full cotyledon beets, (4) May to - to beets, (5) May 7 to - to 6-leaf beets, (6) May to 4- to 8-leaf beets, and (7) May to 4- to 8- leaf beets. Sugar beets were harvested October 6 and 7. ERS = estimated recoverable sucrose. Malheur Ecperiment Station Annual Report 005. Oregon State University. Special Report 070. Pg 7-

41 WEED CONTROL AND CROP RESPONSE WITH OPTION HERBICIDE APPLIED IN FIELD CORN Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Weed control is important in field corn production to reduce competition with the crop and to prevent the production of weed seed for future crops. Field trials were conducted to evaluate Option (foramsulfuron) herbicide applied alone and in various combinations for weed control and crop tolerance in furrow-irrigated field corn. Option is a new postemergence sulfonylurea herbicide that controls annual and perennial grass and broadleaf weeds in field corn. Option contains a safener that is intended to enhance the ability of corn to recover from any yellowing or stunting sometimes associated with the application of sulfonylurea herbicides. Materials and Methods The soil was formed into -inch beds on May 0. Plots were sidedressed with 6 lb nitrogen (N), 4 lb sulfates, lb zinc, lb boron, lb manganese, and 8 lb elemental sulfur/acre on May. Pioneer variety P-6N69 Roundup Ready field corn was planted with a John Deere model 7 Flexi Planter on May 7. Seed spacing was one seed every 7 inches. Plots were 7. by 0 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Herbicide treatments were applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Crop response and weed control were evaluated throughout the growing season. Corn yields were determined by harvesting ears from 6-ft sections of the center rows in each 4-row plot on October. The harvested ears were shelled and grain weight and percent moisture content were recorded. Grain yields were adjusted to percent moisture content. Data were analyzed using analysis of variance (ANOVA) and treatment means were separated using Fisher s protected least significant difference (LSD) at the 5 percent level (P = 0.05). Postemergence treatments of Option, Clarion, or Roundup were applied alone and in combinations with other herbicides and with or without preemergence () Dual Magnum. applications were made May. Mid-postemergence (MP) treatments were applied to corn at the V4 growth stage on June, and late postemergence treatments (LP) were applied to corn at the V6 growth stage on June 9. Option was applied with various additives as well as in combination with Distinct or Callisto. Option combinations were compared to Clarion applied alone and in combination with Distinct or to Roundup applied alone or following Dual Magnum. The herbicide rates and combinations are shown in Table. Results and Discussion Control of pigweed species (i.e., Powell amaranth and redroot pigweed) ranged from 9 to 00 percent on July and was similar among herbicide treatments. One exception was the treatment with Option, Dyne-Amic, and percent N, which provided only 9 percent control (Table ). When Option was applied with Dyne-Amic and percent N or Quest, common lambsquarters control also was lower than all other treatments. Clarion alone also provided less common lambsquarters control Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 4-7

42 than all other treatments except for Option applied with Dyne-Amic. Combinations of Option with Distinct or Callisto, and the combination of Clarion and Distinct provided among the best common lamsquarters control. Common lambsquarters control was improved when Roundup was applied following Dual Magnum compared to Roundup applied alone. Clarion alone provided the least hairy nightshade control, and the combination of Clarion and Distinct also provided less hairy nightshade control compared to all other treatments except Option with Dyne-Amic and percent N. There were no significant differences in kochia and barnyardgrass control among treatments. Injury from herbicide treatments ranged from 0 to 4 percent on June 9 and was 4 percent or less on July (Table ). Corn yields ranged from a low of 0 bu/acre with the untreated control to a high of 94 bu/acre with the combination of Option and Callisto (Table ). The treatment containing Option with Dyne-Amic and percent N had lower yields than many of the other Option treatments and was likely due to reduced weed control with that treatment. The selection of additives can significantly affect the efficacy of Option against pigweed species, common lambsquarters, and hairy nightshade. The addition of Distinct or Callisto to Option can significantly improve common lambsquarters control. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 4-7

43 Table. Weed control with Option herbicide applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Treatment Rate* Timing Pigweed spp C. lambsquarters Weed control H. nightshade Kochia Barnyardgrass lb ai/acre pt/acre % v/v % Option + MSO + % N MP Option + MSO + AMS MP Option + DYNE-AMIC + % N % +.0 MP Option + MSO + QUEST % MP Clarion + MSO + % N MP Option + MSO + % N MP Option + Distinct + MSO + % N MP Option + Distinct + MSO + % N MP Clarion + Distinct + NIS + % N % MP Option + Callisto + MSO + % N MP Dual II Magnum Option + MSO + % N LP Option + MSO + AMS MP Option + DYNE-AMIC + Quest % + MP % Roundup Ultramax 0.58 MP Dual II Magnum Roundup Ultramax + AMS LP LSD (0.05) 6 NS NS *Herbicide rates are in lb ai/acre. Additive rates are in pt/acre or percent v/v. Application timings were preemergence () on May, mid-postemergence (MP) applied to corn at the V4 growth stage on June, and late postemergence (LP) to corn at the V6 growth stage on June 9. Pigweed species were a mixture of Powell amaranth and redroot pigweed. Weed control was evaluated July. The untreated control was not included in the ANOVA for weed control. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 4-7

44 Table. Injury and yield with Option herbicide applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Field corn Injury Yield Treatment Rate* Timing lb ai/acre pt/acre % v/v % bu/acre Untreated control Option + MSO + % N MP Option + MSO + AMS MP Option + DYNE-AMIC + % N % +.0 MP Option + MSO + QUEST % MP Clarion + MSO + % N MP 0 78 Option + MSO + % N MP 9 74 Option + Distinct + MSO + % N MP 0 8 Option + Distinct + MSO + % N MP Clarion + Distinct + NIS + % N % MP 6 89 Option + Callisto + MSO + % N MP Dual II Magnum Option + MSO + % N LP 9 84 Option + MSO + AMS dry MP Option + DYNE-AMIC + Quest % + % MP 0 78 Roundup Ultramax 0.58 MP Dual II Magnum Roundup Ultramax + AMS LP LSD (0.05) *Herbicide rates are in lb ai/acre. Additive rates are in pt/acre or percent v/v. Application timings were preemergence () on May, mid-postemergence (MP) applied to corn at the V4 growth stage on June, and late postemergence (LP) to corn at the V6 growth stage on June 9. The untreated control was not included in the ANOVA for percent injury. Corn was harvested October and yields were adjusted to percent moisture content. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 4-7

45 Evaluations of Spring Herbicide Applications to Dormant Mint Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Weed control in mint is essential in order to maintain high mint oil yields and quality. Reducing competition from weeds may prolong the productive life of a mint stand. Herbicides are important tools for controlling weeds in mint. With the constant loss of herbicides that are registered for use in mint, it is critical to identify replacements that will provide similar weed control. Several new herbicides that have recently become available or may be available in the near future have been tested in mint. This research evaluated herbicides that have been used traditionally with new herbicide combinations containing some recently registered herbicides including Spartan (sulfentrazone), Chateau (flumioxazin), and Command (clomazone). Materials and Methods Two trials were established to evaluate spring herbicide applications to dormant mint for mint tolerance and weed control efficacy. One trial was established near Nampa, Idaho and the other near Nyssa, Oregon. Perennial weed problems and a poor mint stand resulted in abandonment of the Oregon location. Herbicides that were evaluated included a standard of Sinbar, Karmex, Stinger, and Prowl compared to various combinations that included Spartan, Chateau, and Command. Treatments were applied March, 004 when mint was still mostly dormant. Herbicide treatments were arranged in a randomized block design with four replicates. Plots were 0 ft wide by 0 ft long. Herbicides were applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Visual evaluations of mint injury and weed control were made throughout the season. Mint yield was determined by harvesting mint from yd from the center of each plot. After the mint fresh weight was recorded, a 0-lb sub-sample was taken and allowed to dry in burlap bags. Once samples were dry, mint oil was extracted at the University of Idaho mint research still. Distillation was done according to the Mint Industry Research Council (MIRC) protocol. Results and Discussion Only the treatment containing Command, Spartan, and Stinger caused significant mint injury on April 7 (Table ). The same combination with Spartan at a lower rate caused significantly less mint injury, as did the combination of Command, Spartan, and Gramoxone. By June 7, no significant injury was visible for any treatment. Prickly lettuce populations were variable, and variability among prickly lettuce control evaluations resulted in no statistical differences among herbicide treatments. Kochia densities were too low for visual control evaluation, but counts of all the kochia in each plot revealed that all but two treatments significantly reduced kochia numbers compared to the untreated check. The combination of Sinbar, Karmex, Stinger, and Chateau and the combination of Command, Chateau, and Gramoxone did not significantly reduce kochia numbers. Mint fresh weight and oil yields were strongly correlated with prickly lettuce control and kochia densities (Fig. ). All treatments increased mint yield compared to the untreated control. The combination of Command, Chateau, and Gramoxone produced lower mint fresh weight and oil yields than all other treatments except Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 8-0

46 combinations of Command, Spartan, and Gramoxone, but had similar oil yields compared to the combination of Sinbar, Karmex, Singer, and Prowl. Figure. Mint fresh hay and oil yield as influenced by prickly lettuce control (A and B) and kochia density (C and D) in Nampa, ID, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. For all regressions P < Fresh mint yield (lb/yd ) A y = 0.558x +.04 R = Prickly lettuce control (%) Mint oil (lb/acre) B y = 0.647x R = Prickly lettuce control (%) Fresh mint yield (lb/yd ) C y = x x R = Kochia (no./plot) Mint oil (lb/acre) D y = x x R = Kochia (no./plot) Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 8-0

47 Table. Mint injury and weed control from spring herbicide applications to dormant peppermint in Nampa, ID, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Weed control Kochia Mint yield Mint injury Prickly lettuce density Fresh Wt. Oil Treatment* Rate lb ai/acre % no/plot lb/ yd lb/acre Untreated control a Sinbar + Karmex + Stinger + Prowl + NIS % b Sinbar + Karmex + Stinger + Spartan + NIS % b.0 95 Sinbar + Karmex + Stinger + Chateau + NIS % ab Command + Spartan + Stinger + NIS % b.0 0 Command + Chateau + Stinger + NIS % b.6 84 Command + Spartan + Gramoxone Extra + NIS % b Command + Chateau + Gramoxone Extra + NIS % ab Sinbar + Karmex + Stinger + Spartan + NIS % b Command + Spartan + Stinger + NIS % b. 97 Command + Spartan + Gramoxone Extra + NIS % b Command + Spartan + Stinger + Buctril + NIS % b LSD (0.05) 0 NS NS NS NS *Treatments were applied March, 004 to dormant mint. Herbicide rates are lb ai/acre. NIS (nonionic surfactant, Activator 90) was applied at percent v/v. Mean separation is based on transformed data. Raw data are presented. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 8-0

48 WEED CONTROL IN ONION WITH POSTEMERGENCE HERBICIDES Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Weed control is essential for the production of marketable onions. Weed control in onions is difficult compared to many crops because of the lack of a complete crop canopy and limited herbicide options. Chateau (flumioxazin), formerly called Valor, and Nortron (ethofumesate) are two experimental herbicides that have been evaluated for use in onions in past research trials. Trials were conducted this year to determine the benefits of using these experimental herbicides in postemergence herbicide combinations and compare their performance to registered herbicide combinations. Methods General Procedures Trials were conducted at the Malheur Experiment Station to evaluate experimental and registered herbicides for weed control and onion tolerance. Trials were conducted under furrow irrigation. On March 5, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at.7-inch spacing in double rows on -inch beds. Plots were 4 rows wide and 7 ft long and arranged in a randomized complete block design with four replications. Lorsban was applied in a 6-inch band over each double row at.7 oz/,000 ft of row. Onions were sidedressed with 75 lb nitrogen (N), 0 lb phosphorus (P), 5 lb sulfate, 8 lb sulfur (S), lb Zinc (Zn), lb manganese (Mn), and lb boron (B)/acre on June. Registered insecticides and fungicides were applied for thrips and downy mildew control. Herbicide treatments were applied with a CO -pressurized backpack sprayer. Preemergence applications and postemergence grass herbicides were applied at 0 gal/acre at 0 psi and postemergence treatments were applied at 40 gal/acre at 0 psi. All plots were treated with a preemergence application of Roundup (glyphosate) at 0.75 lb ai/acre plus Prow l (pendimethalin) at.0 lb ai/acre on April 5 and a postemergence application of Poast (sethoxydim) at 0.9 lb ai/acre plus crop oil concentrate (COC) (.0% v/v) on June 6. Postemergence treatments were applied to two-leaf onions on May 6, two- to three-leaf onions on May 4, and to five-leaf onions on June. In the Chateau application timing trial, a separate application of Chateau was made to three-leaf onions on May 8. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 6 and 7 and graded by size on October -4. Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Comparison of Postemergence Chateau or Combinations Chateau and (oxyflurofen) were applied in combinations with Buctril (bromoxynil) to evaluate weed control and onion tolerance. Buctril,, and Chateau were evaluated at two rates. Comparisons of or Chateau with Buctril included several combinations of herbicides and rates. Additional treatments included a split application of Chateau applied to two-leaf and again to three- Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

49 leaf onions, and a comparison of Buctril plus Chateau treatments following preemergence applications of Roundup, Prowl, and Dacthal (DCPA). Application Timings for Chateau Chateau was applied at two rates in combination with Buctril to two-leaf or three-leaf onions. Chateau treatments were compared to plus Buctril. Additional treatments included Chateau in a separate application 4 days after the Buctril application at the three-leaf application timing. Addition of Nortron to Postemergence Treatments This trial was conducted to determine if the addition of Nortron to postemergence herbicide applications would improve weed control. Each treatment was applied with or without Nortron added to the two-leaf and three-leaf applications at either or 0.5 lb ai/acre. One treatment evaluated Outlook (dimethenamid-p) added to the two-leaf application and Nortron added to the three-leaf application. Results and Discussion Preemergence herbicides worked fairly well due to rainfall in April. Adequate rainfall also ensured that weeds were actively growing when postemergence treatments were applied. Comparison of Postemergence Chateau or Combinations Because the preemergence application of Prowl was so effective, there were no differences in weed control between any of the postemergence herbicide treatments (Table ). Control of all species was 85 percent or greater. There were also no differences in onion injury among treatments. This is surprising as there were large differences in the herbicide rates applied for different treatments. There were a few differences in onion yields, with higher yields resulting from treatments with additional soil-active herbicides applied or with higher rates (Table ). Application Timings for Chateau Treatment with Chateau combined with Buctril when applied either to two-leaf or three-leaf onions did not cause greater injury than combinations of plus Buctril (Table ). When Chateau was applied alone 4 days after Buctril was applied to three-leaf onions, injury increased significantly. By July there were no differences in onion injury among treatments. The injury caused by the delayed application of Chateau was probably related to wet cool weather that occurred after the Buctril application and prior to the Chateau application. Pigweed (redroot pigweed and Powell amaranth), common lambsquarters, hairy nightshade, and barnyardgrass control was not different among herbicide treatments and was 88 percent control or greater. Kochia control was significantly greater with treatments that contained Chateau tank-mixed with Buctril and applied at either the two-leaf or three-leaf timing compared to Buctril plus. Treatments where Chateau was applied alone following the Buctril application to three-leaf onions did not control weeds better than Buctril plus. There were few significant differences in onion yields between herbicide treatments, with marketable yields ranging from,07 to,459 cwt/acre. Addition of Nortron to Postemergence Treatments Onion injury was not different among treatments on either evaluation date (Table 5). Pigweed, hairy nightshade, and barnyardgrass control was similar among herbicide treatments and was 89 percent or higher. The addition of Nortron at either rate to Buctril significantly increased common Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

50 lambsquarters control, but control was similar to that provided by plus Buctril. There was no improvement in common lambsquarters control when Nortron was added to Buctril plus. Kochia control was less when Buctril was applied alone compared to treatments containing Buctril plus Nortron or or both. A few of the treatments containing Nortron produced more supercolossal onions than did Buctril alone, but yields were similar to the other herbicide treatments (Table 6). Nortron is useful for improving weed control in onion but in this trial did not provide greater benefits than the currently registered herbicides. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

51 Table. Onion injury and weed control from or Chateau combinations with Buctril, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Injury Weed control Treatment Rate Timing* Pigweed Common lambsquarters Hairy Barnyardgrass Kochia nightshade lb ai/acre Leaf % Untreated Roundup + Prowl Buctril Roundup + Prowl Buctril Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Roundup + Prowl Roundup + Prowl leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

52 Table (continued). Onion injury and weed control from or Chateau combinations with Buctril, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Injury Weed control Treatment Rate Timing* Pigweed Common lambsquarters Roundup + Prowl Roundup + Prowl Buctril + Chateau Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau Hairy Barnyardgrass Kochia nightshade lb ai/acre Leaf % leaf 5-leaf 5-leaf 5-leaf 5-leaf LSD (P = 0.05) NS NS NS NS NS NS NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, and five-leaf (5-leaf) on June. Weed-control ratings were taken September. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

53 Table. Onion yield in response to or Chateau combinations with Buctril, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Roundup + Prowl Buctril Roundup + Prowl Buctril Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Roundup + Prowl Roundup + Prowl leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf , , , , , , , , ,04 Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

54 Table (continued). Onion yield in response to or Chateau combinations with Buctril, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable Roundup + Prowl Roundup + Prowl Buctril + Chateau Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau Roundup + Dacthal + Prowl Buctril + Chateau lb ai/acre Leaf cwt/acre leaf 5-leaf 5-leaf 5-leaf 5-leaf , , , , , LSD (P = 0.05) *Preemergence () treatment applied on April 5, two-leaf () on May 6, three-leaf () on May 4, and five-leaf (5-leaf) on June. Onions were harvested on September 6 and 7. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

55 Table. Weed control and onion injury in response to Chateau application timings, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Injury Treatment Rate Timing* Pigweed Common lambsquarters Weed control Hairy nightshade Kochia Barnyardgrass Untreated lb ai/acre -- Leaf % Roundup + Prowl leaf Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau leaf 5-leaf 5-leaf 5-leaf Roundup + Prowl Buctril Chateau (S) 5-leaf Roundup + Prowl Buctril Chateau (S) 5-leaf LSD (P = 0.05) NS NS NS NS 5 NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, three-leaf separate ( (S)) on May 8, and five-leaf (5-leaf) on June. Weed control ratings were taken September. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

56 Table 4. Onion yield in response to Chateau application timings, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Roundup + Prowl Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril + Chateau Roundup + Prowl Buctril Chateau Roundup + Prowl Buctril Chateau leaf 5-leaf 5-leaf 5-leaf 5-leaf (S) 5-leaf (S) 5-leaf , , , , , , ,45 LSD (P = 0.05) *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, three-leaf separate ( (S)) on May 8, and five-leaf (5-leaf) on June. Onions were harvested on September 6 and 7. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

57 Table 5. Onion injury and weed control in response to the addition of Nortron to postemergence applications of Buctril and, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Treatment Rate Timing * Injury Pigweed Common lambsquarters Weed control Hairy Barnyard- Kochia nightshade grass % Lb ai/acre Leaf Untreated Roundup + Prowl Buctril Roundup + Prowl Roundup + Prowl Buctril + Nortron Nortron Roundup + Prowl Buctril + Nortron + Nortron Roundup + Prowl Nortron Nortron Roundup + Prowl Outlook + Nortron Roundup + Prowl Nortron Nortron leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf LSD (P = 0.05) NS NS NS 7 NS NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, and five-leaf (5-leaf) on June. Weed control ratings were taken September. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

58 Table 6. Onion yield in response to the addition of Nortron to postemergence applications of Buctril and, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable Untreated lb ai/acre -- Leaf cwt/acre Roundup + Prowl Buctril leaf Roundup + Prowl Roundup + Prowl Buctril + Nortron + Nortron Roundup + Prowl Buctril + Nortron + Nortron Roundup + Prowl + Nortron + Nortron Roundup + Prowl + Outlook + Nortron Roundup + Prowl + Nortron + Nortron leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf , , , , , ,9 LSD (P = 0.05) *Preemergence () treatment applied on April 5, two-leaf () on May 4, three-leaf () on May 8, and five-leaf (5-leaf) on June. Onions were harvested on September 6 and 7. The information in this report is for the purpose of informing cooperators in industry, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any pesticide. Pesticide labels should always be consulted before any pesticide use. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 54-64

59 SOIL-ACTIVE HERBICIDE APPLICATIONS FOR WEED CONTROL IN ONION Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Weed control is essential for the production of marketable onions. Only a few herbicides are registered for preemergence application in onion. Effective preemergence herbicides can control weeds as they germinate and reduce the size and number of weeds that are present when onions are large enough to tolerate postemergence herbicide applications. This research evaluated registered and experimental herbicides for preemergence weed control in onion. Methods General Procedures A trial was conducted at the Malheur Experiment Station under furrow irrigation. On March 5, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at.7-inch spacing in double rows on - inch beds. Plots were 4 rows wide and 7 ft long and arranged in a randomized complete block design with 4 replicates. Lorsban was applied in a 6-inch band over each double row at.7 oz/,000 ft of row. Onions were sidedressed with 75 lb nitrogen, 0 lb phosphorus, 5 lb sulfate, 8 lb elemental sulfur, lb zinc, lb manganese, and lb boron/acre on June. Registered insecticides and fungicides were applied for thrips and downy mildew control. Preemergence () applications of Prowl (pendimethalin), Nortron (ethofumesate), and Outlook (dimethenamid-p) in combination with Roundup (glyphosate) were evaluated for weed control and onion tolerance. Each product was evaluated at two rates. Combinations of Prowl with Nortron or Outlook were also evaluated. Prowl and Prowl H 0 (a new water-based formulation) were also applied to onions at the flag leaf stage following Roundup applied. Prowl H 0 was also combined with Outlook applied at the flag leaf stage following a application of Roundup. Preemergence treatments and other applications of soil-active herbicides were compared to plots where only Roundup was applied preemergence. Herbicide treatments were applied with a CO -pressurized backpack sprayer. Preemergence applications were applied at 0 gal/acre at 0 psi. Postemergence applications were applied at 40 gal/acre at 0 psi. Preemergence treatments were applied on April 5, two-leaf on May 6, three-leaf on May 4, and five-leaf on June. All plots received Poast (sethoxydim) at 0.9 lbs ai/acre plus crop oil concentrate (COC) ( qt/acre) on June 6 to control grasses. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 6 and 7 and graded by size on October -4. Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

60 Results and Discussion Preemergence and postemergence treatments were effective because of rain and actively growing weeds at the time herbicides were applied. Injury was similar among treatments except for plots treated with a tank mixture of Buctril, Outlook, and Chateau, which had significantly more injury than all other treatments on May 4 and at the later evaluation on June 9 (Table ). Pigweed (redroot pigweed and Powell amaranth) control was similar among herbicide treatments and ranged from 84 to 99 percent. Common lambsquarters control was improved with preemergence applications of Prowl compared to plots treated only with Roundup. Outlook and Nortron did not significantly increase common lambsquarters control compared to Roundup alone. Hairy nightshade control was greater than 90 percent and barnyardgrass greater than 96 percent for all herbicides. Kochia control was significantly greater with Prowl or Nortron compared to Outlook. However, the high rate of Outlook improved kochia control compared to Roundup alone. This year, delaying Prowl or Prowl plus Outlook combinations until the flag leaf stage provided similar control to preemergence applications. If these treatments are as effective as the applications, then applications to flag leaf onions provide an increased level of crop safety compared to applications. Treatments with Prowl applied or to flag leaf onions followed by applications of Outlook to two-leaf onions also effectively controlled all weeds. The Prowl label allows applications to flag leaf onions and the Outlook label allows applications to two-leaf onions. Roundup alone and Roundup plus Outlook (0.66 lb ai/acre) produced higher medium onion yields and lower colossal, total, and marketable onion yields compared to all the other treatments (Table ). The combination of Prowl plus Outlook had among the lowest number of onion bulbs per acre and was less than plots with Roundup alone or applications of Prowl made to flag leaf onions. This result illustrates the potential to reduce onion stand with applications of soil-active herbicides. Even with the reduced number of onion bulbs, this treatment produced yields similar to all other treatments. Only plots with reduced weed control had significantly lower yields. The increased weed control and subsequent increase in onion yields from plots receiving a or flag leaf application of a soil-active herbicide demonstrates the importance of soil-active herbicides for reducing weed germination and growth prior to when postemergence herbicide applications can be made. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

61 Table. Onion injury and weed control in response to applications of Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Treatment Rate Timing * Injury Weed control Pigweed Common lambsquarters Hairy nightshade lb ai/acre Leaf % Untreated Roundup + Outlook leaf Roundup + Outlook Roundup + Nortron Roundup + Nortron Roundup + Prowl Roundup + Prowl Roundup Roundup + Prowl + Nortron Roundup + Prowl + Outlook leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf Kochia Barnyard grass Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

62 Table (continued). Onion injury and weed control in response to applications of Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Treatment Rate Timing * Pigweed Roudup Prowl + Outlook Roundup Prowl HO + Outlook Roundup Prowl + Outlook Roundup Prowl HO + Outlook Roundup + Prowl + Outlook Injury Weed control Common lambsquarters Hairy nightshade Kochia Barnyard grass lb ai/acre Leaf % Flag 5-leaf Flag 5-leaf Flag 5-leaf Flag 5-leaf 5-leaf Roundup + Prowl Buctril + Chateau + Outlook leaf LSD (0.05) *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, and five-leaf (5-leaf) on June. Weed control was evaluated on September. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

63 Table. Onion yield in response to applications of Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing * Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Roundup + Outlook Roundup + Outlook Roundup + Nortron Roundup + Nortron Roundup + Prowl Roundup + Prowl Roundup Roundup + Prowl + Nortron Roundup + Prowl + Outlook leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf 5-leaf Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

64 Table (continued). Onion yield in response to applications of Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Onion yield Treatment Rate Timing * Small Medium Jumbo Colossal S. Colossal Marketable Untreated lb ai/acre -- Leaf cwt/acre Roundup 0.75 Prowl + Outlook Flag leaf Roundup Prowl HO + Outlook Roundup Prowl + Outlook Roundup Prowl HO + Outlook Roundup + Prowl + Outlook Roundup + Prowl Buctril + Chateau + Outlook Flag 5-leaf Flag 5-leaf Flag 5-leaf 5-leaf 5-leaf LSD (0.05) *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 4, and five-leaf (5-leaf) on June. Onions were harvested on September 6 and 7. The information in this report is for the purpose of informing cooperators in industry, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any pesticide. Pesticide labels should always be consulted before any pesticide use. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 65-70

65 DEVELOPMENT OF NEW HERBICIDE OPTIONS FOR WEED CONTROL IN POTATO PRODUCTION Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Weed control in potatoes is essential for production of high yielding marketable tubers. Herbicide options in potato production are limited. Outlook, Spartan, and Chateau (previously Valor ) demonstrate great promise for use in potato. Spartan and Chateau represent a mode of action that is not currently used in potatoes and offer excellent hairy nightshade control. Outlook (dimethenamid-p) has the same mode of action as Dual but controls a wider spectrum of weeds. Trials were conducted to evaluate new herbicides for weed control in potatoes. The results of our research have been provided to herbicide companies, the IR4 program, and state regulators in support of additional herbicide registrations in potatoes. Spartan was registered for use in potato in 004 and Outlook is registered for use in potato in 005. Chateau is also registered for use in potato and will be available in limited quantities for commercial evaluation for 005. The registration of these herbicides gives producers additional tools for controlling weeds and may increase economic returns through improved weed control. Materials and Methods Three trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes: Spartan alone and in - and -way tank mixtures; comparisons of standard -way tank mixtures with Chateau or Matrix added in -way tank mixtures; and Outlook in - and -way tank mixtures. In fall 00, 50 lb nitrogen (N) and 00 lb phosphorus (P)/acre was applied prior to bedding in all trial areas. On October 7, 00, Telone II (0 gal/acre) and Vapam (0 gal/acre) were applied and the ground was bedded. Potatoes were planted April 7, 004 in an Owyhee silt loam soil with ph 7.6,.7 percent organic matter content, and a cation exchange capacity of 9. Russet Burbank seed pieces were planted every 9 inches in 6-inch-wide rows. Seed pieces were treated with Tops-MZ plus Gaucho. Experimental plots were 4 rows wide and 0 ft long. Plots were sidedressed with 0 lb N, 4 lb P, 9 lb potassium (K), 8 lb sulfate, lb elemental sulfur (S), 5 lb zinc (Zn), and lb boron (B)/acre on May and rehilled on May. Preemergence herbicides were applied with a CO -pressurized backpack sprayer delivering 0 gal/acre at 0 psi and incorporated with approximately 0.5 inch of sprinkler irrigation on May. Petiole samples were taken and sent for nitrate analysis on July. On July 6, 5 lb N/acre was applied through the sprinkler. Aerial fungicide applications included Bravo and Ridomil Gold on June, Headline ( oz/acre) on June 6, Topsin-M (0 oz/acre) plus liquid sulfur (6 lb/acre) on July 7, and Headline ( oz/acre) plus liquid sulfur (6 lb/acre) on August 8. In addition,.5 lb P and 0. lb Zn/acre were added to the July 7 fungicide application. Visual potato injury and weed control were evaluated throughout the growing season and tubers were harvested from the center two rows of each plot on September -5. Potatoes were graded for yield and size on September 0-7. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

66 Herbicide screening for activity on dodder Herbicides were screened in a petri dish assay to determine effects on dodder germination and elongation. Dodder seeds were scarified using sandpaper and 0 seeds were placed in each petri dish. Each dish was treated with 6 ml of water containing herbicides at rates equivalent to what would be applied in the field. Dodder germination was counted 4 and 5 days after treatment (DAT), and dodder shoot length was measured 5 DAT. Results and Discussion Spartan alone and in - and -way tank mixtures Control of all weeds present in this trial was 9 percent or greater by treatments with Spartan alone or combined with other herbicides (Table ). Spartan caused potato injury on June 9, consisting of interveinal chlorosis and necrosis on one set of leaves, and injury tended to be greater with higher rates of Spartan (Table ). No differences in potato yield were observed between herbicide treatments, suggesting that the injury was transient (Table ). Comparisons of standard -way tank mixtures with Chateau or Matrix added in -way tank mixtures The -way tank mixtures provided the same level of control as -way tank mixtures including either Chateau or Matrix (Table ). The exception was the combination of Prowl plus Eptam, where pigweed control was increased with the addition of Matrix. The -way combination of Prowl, Eptam, and Chateau had lower pigweed and barnyardgrass control than most other treatments. Plots treated with Chateau exhibited severe injury on May 6 (Table ). Injury symptoms included stunting and crinkling of newly emerged shoots and leaves. Rainfall events at the time of potato emergence may have increased the contact of Chateau with the emerging foliage. Some treatments were still causing significant injury on June 9. In one instance, the combination of Prowl, Eptam, and Chateau yielded lower than Prowl plus Eptam (Table 4). This could have been a result of the early injury when Chateau was in the tank mixture. Outlook in - or -way tank mixtures Outlook combined with Prowl or Sencor in -way tank mixtures or with both in a -way tank mixture provided 96 percent or greater control of all weeds (Table 5). Potato yields were not different among herbicide treatments (Table 6). Herbicide screening for activity on dodder Only Nortron suppressed dodder germination compared to the untreated check (Table 7). However, all herbicides except Chateau shortened shoot length compared to the untreated check. Nortron caused the greatest reduction followed by Kerb, Prowl, Spartan, and Dacthal. Nortron and Kerb are not registered for use in potato. The fact that Prowl and Spartan reduced dodder shoot growth suggests they may be useful in managing dodder in potatoes. In this trial, both Prowl and Spartan rates were higher than those registered for use in potato. Additional research needs to be done with Prowl and Spartan rates that are used in potato production. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

67 Table. Effect of Spartan alone and in combinations on crop injury and weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Weed control Potato injury Common Hairy Barnyard Treatment* Rate Pigweed lambsquarters nightshade Kochia grass % lb ai/acre Untreated check Spartan Spartan Spartan Spartan + Prowl Spartan + Prowl Spartan + Dual Magnum Spartan + Dual Magnum Spartan + Outlook Spartan + Outlook Spartan + Eptam Spartan + Eptam Spartan + Prowl + Eptam Spartan + Prowl + Dual Magnum Spartan + Prowl + Outlook LSD (P = 0.05) NS 9 NS NS NS NS NS *Herbicide treatments were applied preemergence on May, 004. Weed control evaluations were taken September. Pigweed species were a combination of Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

68 Table. Effect of Spartan alone and in combinations on potato yield and quality, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Potato yield U.S. No. Treatment* Rate 4-6 oz 6- oz > oz Total Percent Total No. Total marketable Total yield lb ai/acre cwt/acre % cwt/acre Untreated check Spartan Spartan Spartan Spartan + Prowl Spartan + Prowl Spartan + Dual Magnum Spartan + Dual Magnum Spartan + Outlook Spartan + Outlook Spartan + Eptam Spartan + Eptam Spartan + Prowl + Eptam Spartan + Prowl + Dual Magnum Spartan + Prowl + Outlook LSD (P = 0.05) -- NS *Herbicide treatments were applied preemergence on May, 004. Potatoes were harvested September to 5. Total marketable yield = total number ones + total number twos. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

69 Table. Comparison of standard -way tank mixtures with Chateau or Matrix added in -way tank mixtures for potato crop injury and weed control, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Weed control Potato injury Common Hairy Treatment* Rate Pigweed lambsquarters nightshade Kochia Barnyard grass lb ai/acre % Untreated check Dual Magnum + Sencor Prowl + Sencor Dual Magnum + Prowl Prowl + Eptam Dual Magnum + Sencor + Chateau Sencor + Prowl + Chateau Dual Magnum + Prowl + Chateau Prowl + Eptam + Chateau Dual Magnum + Sencor + Matrix Sencor + Prowl + Matrix Dual Magnum + Prowl + Matrix Prowl + Eptam + Matrix LSD (P = 0.05) NS NS NS 4 *Herbicide treatments were applied preemergence on May, 004. Weed control evaluations were taken September. Pigweed species were a combination of Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

70 Table 4. Effect of standard -way tank mixtures with Chateau or Matrix added in -way tank mixtures on potato yield and quality, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Potato yield U.S. No. Treatment* Rate 4-6 oz 6- oz > oz Total Percent Total No. Total marketable Total yield Lb ai/acre cwt/acre % cwt/acre Untreated check Dual Magnum + Sencor Prowl + Sencor Dual Magnum + Prowl Prowl + Eptam Dual Magnum + Sencor + Chateau Sencor + Prowl + Chateau Dual Magnum + Prowl + Chateau Prowl + Eptam + Chateau Dual Magnum + Sencor + Matrix Sencor + Prowl + Matrix Dual Magnum + Prowl + Matrix Prowl + Eptam + Matrix LSD (P = 0.05) -- NS *Herbicide treatments were applied preemergence on May, 004. Potatoes were harvested September to 5. Total marketable yield = total number ones + total number twos. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

71 Table 5. Potato injury and weed control with Outlook, Prowl H O, and Sencor combinations, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Potato injury Treatment* Rate Pigweed Common lambsquarters Weed control Hairy nightshade Kochia Barnyard grass lb ai/acre % Untreated check Prowl H O + Outlook Prowl H O + Outlook Outlook + Sencor Outlook + Sencor Prowl H O + Outlook Sencor Prowl H O + Outlook Sencor LSD (P = 0.05) -- 5 NS NS NS NS NS NS *Herbicide treatments were applied preemergence on May, 004. Weed control evaluations were taken September. Pigweed species were a combination of Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

72 Table 6. Influence of Outlook, Prowl H O, and Sencor combinations on potato yield and quality, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Potato yield U.S. No. Total Total Total Treatment* Rate 4-6 oz 6- oz > oz Total Percent No. marketable yield lb ai/acre cwt/acre % cwt/acre Untreated check Prowl H O + Outlook Prowl H O + Outlook Outlook + Sencor Outlook + Sencor Prowl H O + Outlook + Sencor Prowl H O + Outlook + Sencor LSD (P = 0.05) -- NS *Herbicide treatments were applied preemergence on May, 004. Potatoes were harvested September to 5. Total marketable yield = total number ones + total number twos. Table 7. Dodder germination and shoot length in response to herbicides in a petri-dish screening trial, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Dodder Treatment* Germination Shoot Equivalent rate Rate 4 DAT 5 DAT length lb ai/acre mg ai/liter % mm---- Untreated Prowl Kerb Dacthal Chateau Matrix Spartan Nortron LSD (P=0.05) *Herbicide treatments were applied in 5 ml of water on August, 004. Dodder shoot length was measured only on shoots that had emerged by 4 DAT. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

73 COMPARISON OF CALENDAR DAYS AND GROWING DEGREE-DAYS FOR SCHEDULING HERBICIDE APPLICATIONS IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR 004 Introduction Timely herbicide application is critical to achieve effective weed control in sugar beet. Often, the amount of time between sequential herbicide applications is based on a given number of calendar days since the prior herbicide application. Under most circumstances this approach works well. When spring weather is cooler than normal, applying herbicides on a calendar day schedule may result in applications too close together. This can result in greater injury to the beets or herbicides being applied before they are needed. Since weed and beet growth depend on temperature, it is logical that using accumulated growing degree-days (GDD) to schedule herbicide applications may be superior to calendar days. GDD accounts for variations in the weather and gives a more accurate idea of how fast plants are growing. If the weather is ideal for weed and beet growth, herbicide applications are made closer together; if the weather is cool, then applications are spaced further apart. Evaluation of a GDD model for timing herbicide applications may provide producers with a tool to improve the efficacy of the herbicides they are using. Methods A trial was established at the Malheur Experiment Station under furrow irrigation on April 8, 004. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at -inch seed spacing. On April 9, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6-oz/,000 ft of row. Sugar beets were thinned to an 8-inch spacing on May 0 to. Plots were sidedressed on June with 75 lb nitrogen (N) (urea), 0 lb potash (K O), 5 lb sulfates (SO 4 ), 8 lb elemental sulfur (S), lb manganese (Mn), lb zinc (Zn), and lb/acre boron (B). All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On May 6, Temik 5G (4 lb prod/acre) was applied for sugar beet root maggot control. Poast at 6 oz/acre plus crop oil concentrate at qt/acre were applied to the trial area on June 6. For powdery mildew control, Headline ( fl oz/acre) was applied on June 5, Topsin M (0 oz prod/acre) plus S at 6 lb/acre, phosphate (P O 5 ) at.5 lb/acre, and Zn at 0. lb/acre were applied on August 4, and Headline ( fl oz/acre) plus S at 6 lb/acre were applied on August 8. All fungicide treatments were applied by air. Herbicide treatments were broadcast applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were 4 rows wide and 7 ft long and treatments were arranged in a randomized complete block design with 4 replicates. Standard rate, increased standard rate, and micro-rate treatments were compared when applied on fixed calendar day schedules or when applied on different GDD accumulation schedules. The standard and high-standard-rate treatments were applied every 7 or 0 days and these timings were compared to applications at 50, 75, or 5 accumulated GDD since the previous application. The micro-rate treatments were applied on a 5- or 7-day schedule or at 50, 75, or 5 GDD since the previous application. Growing degree-days were calculated on a base of 4 o F using the equation GDD = [(daily high temperature daily low temperature)/] 4. GDD were calculated beginning the Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

74 day after each herbicide application. Herbicide application dates and GDD measured between applications are shown in Table. Table. Application dates for herbicide treatments applied to sugar beet on calendar day or growing degree-day (GDD) schedules, Malheur Experiment Station, Ontario, OR, 004. Application Treatment* Timing st nd rd 4 th Calendar date (GDD since previous application) Standard/High Rate 7 Day 4/ 4/6 5/ 5/0 -- Standard/High Rate 0 Day 4/ 4/6 5/6 5/6 -- Standard/High Rate 50 GDD 4/ 4/6 5/ (5) 5/0 (99) -- Standard/ High Rate 75 GDD 4/ 4/6 5/4 (87) 5/ (7) -- Standard/High Rate 5 GDD 4/ 4/6 5/6 (5) 5/7 (8) -- Micro-rate 5 Day 4/ 4/ 4/9 5/4 5/9 Micro-rate 7 Day 4/ 4/ 5/ 5/8 5/5 Micro-rate 50 GDD 4/ 4/ 5/ (5) 5/7 (64) 5/5 (5) Micro-rate 75 GDD 4/ 4/ 5/ (80) 5/9 (06) 5/ (0) Micro-rate 5 GDD 4/ 4/ 5/4 (49) 5/ (0) 5/6 (8) *Standard and high-standard-rate treatments were applied on the same dates. Application timing based on GDD were determined by calculating the number of GDD beginning the day after the previous application, using the equation GDD = [(daily high temperature daily low temperature)/] 4. Sugar beet injury was evaluated on May 9 and June 9, and weed control was evaluated on September. Sugar beet yields were determined by harvesting the center two rows of each plot on October 8 and 9. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Syngenta Seeds Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion For the standard and high-rate herbicide treatments, the number of days between herbicide applications was the same for the 7-day schedule and the 50-GDD schedule. Applications on the 0-day schedule were within a day of the applications based on 5 GDD. The 75-GDD-spray schedule was between the other schedules. The final application of the standard and high rate herbicide treatments varied by as much as 7 days between application schedules. For micro-rate treatments, the 5-day application schedule was shorter than all other application schedules with the final application made by May 9. The 7-day application timing was almost the same as the timing based on 50-GDD. Applications based on 75 GDD were generally to 7 days later than the 50- GDD schedule and applications with the 5-GDD schedule were likewise delayed to 4 days Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

75 compared to 75 GDD. The final application date among the different application schedules varied by as much as 7 days. In different years, the GDD application schedules could be significantly different from the fixed day application timings, depending on the weather patterns. Postemergence treatments were very effective this year and timing had little effect on weed control. Pigweed and common lambsquarters control were reduced when the micro-rate was applied on a 5-GDD interval compared to all other treatments (Table ). All other treatments and timings provided 94 percent or higher control of pigweed, common lambsquarters, hairy nightshade, kochia, and barnyardgrass. It is surprising that such a wide range of application timings could produce such complete control of all species. Since the standard rate was so effective, no differences were observed between the standard rate and the high-standard-rate treatments. On May 4, injury from the standard or high-standard-rate treatments was among the greatest with the 75-GDD-application timing (Table ). This does not appear to be related to the interval between herbicide applications, but seems to be related to rainfall events preceding those herbicide applications. There was no difference in sugar beet injury among the micro-rate treatments. By June 9, there were no differences in sugar beet injury between any of the herbicide treatments or application timings. All herbicide treatments increased sugar beet root yield and estimated recoverable sugar compared to the untreated check (Table ). There were no differences in percent extraction or sugar content for any treatment. Root yields were not different among the herbicide treatments and application timings. The high rate applied on a 0-day interval produced more estimated recoverable sucrose than the standard rate applied on the same 0-day schedule or the micro-rate applied on the 5-GDDapplication schedule. This year application timing was not critical because the postemergence treatments worked very well. In addition, the initial postemergence applications were made at the correct time while weeds were small. If the initial timing is delayed, the time between subsequent applications may be much more critical. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

76 Table. Weed control in sugar beet with standard rate, high-standard-rate, and micro-rate herbicide treatments applied on a calendar day schedule or at different growing degree-day (GDD) intervals, Malheur Experiment Station, Ontario, OR, 004. Treatment* Rate Timing spp. Pigweed Standard Rate Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Common lambsquarters Weed control Hairy nightshade Kochia oz ai/acre or % v/v % Barnyardgrass 7 Day Standard Rate Same as above 0 Day Standard Rate Same as above 50 GDD Standard Rate Same as above 75 GDD Standard Rate Same as above 5 GDD Micro-Rate Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO % v/v % v/v % v/v % v/v 5 Day Micro-Rate Same as above 7 Day Micro-Rate Same as above 50 GDD Micro-Rate Same as above 75 GDD Micro-Rate Same as above 5 GDD High Rate Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Day High Rate Same as above 0 Day High Rate Same as above 50 GDD High Rate Same as above 75 GDD High Rate Same as above 5 GDD LSD (P = 0.05) NS NS NS *Standard and high-standard-rate treatments were applied on the same dates. Application timing based on GDD were determined by calculating the number of GDD beginning the day after the previous application using the equation GDD = [(daily high temperature daily low temperature)/] 4. Weed control was evaluated September. Pigweed species are a mixture of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

77 Table. Sugar beet injury and yield with standard rate, high-standard-rate, and micro-rate herbicide treatments applied on a calendar day schedule or at different growing degree-day (GDD) intervals, Malheur Experiment Station, Ontario, OR, 004. Injury Treatment* Rate Timing Sugar beet Yield Root yield Extraction Sucrose ERS -- oz ai/acre or % v/v % ---- ton/acre % lbs/acre Untreated control ,9 Standard Rate Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Day ,00 Standard Rate Same as above 0 Day ,4 Standard Rate Same as above 50 GDD Standard Rate Same as above 75 GDD Standard Rate Same as above 5 GDD Micro-Rate Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO % v/v % v/v % v/v % v/v , , ,409 5 Day ,568 Micro-Rate Same as above 7 Day ,5 Micro-Rate Same as above 50 GDD Micro-Rate Same as above 75 GDD Micro-Rate Same as above 5 GDD High Rate Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger , , ,98 7 Day ,96 High Rate Same as above 0 Day , 50 High Rate Same as above GDD ,85 75 High Rate Same as above GDD ,09 5 High Rate Same as above GDD ,4 LSD (P = 0.05) -- 9 NS 4.4 NS NS,459 *Standard and high standard rate treatments were applied on the same dates. Application timing based on GDD were determined by calculating the number of GDD beginning the day after the previous application using the equation GDD = [(daily high temperature daily low temperature)/] 4. Sugar beets were harvested October 8 and 9. ERS = estimated recoverable sucrose. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 77-85

78 KOCHIA CONTROL WITH EMERGENCE NORTRON IN STANDARD AND MICRO-RATE HERBICIDE PROGRAMS IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction The distribution of kochia resistant to UpBeet (triflusulfuron) herbicide and other acetolactate synthase (ALS) inhibitors (i.e., sulfonylureas, imidazolinones, and triazolopyrimidines) has increased in recent years and poses a serious problem in sugar beet production, as none of the currently registered postemergence herbicides effectively control ALS-resistant kochia. In this trial, Nortron (ethofumesate) was evaluated for preemergence control of kochia in sugar beet. Nortron is a soilactive herbicide used preemergence or early postemergence to control annual grasses and broadleaf weeds. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 8, 004. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April 9, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May 0 to. Plots were sidedressed on June with 75 lb nitrogen (urea), 0 lb potash (K O), 5 lb sulfates (SO 4 ), 8 lb elemental sulfur (S), lb manganese (Mn), lb zinc (Zn), and lb/acre boron (B). All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On May 6, Temik 5G (4 lb prod/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 5, Topsin M (0 oz prod/acre) plus S at 6 lb/acre, phosphate (P O 5 ) at.5 lb/acre, and Zn at 0. lb/acre were applied August 4, and Headline ( fl oz/acre) plus S at 6 lb/acre were applied August 8. All fungicide treatments were applied by air. Herbicide treatments were broadcast-applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were 4 rows wide and 7 ft long and treatments were arranged in a randomized complete block design with 4 replicates. The treatments in this trial consisted of both standard and micro-rate postemergence weed control programs applied with or without a preemergence application of Nortron at either 6, 4, or oz ai/acre with and without postemergence UpBeet. For the micro-rate treatment without UpBeet, Nortron was also applied preemergence at 48 oz ai/acre. UpBeet was omitted from selected treatments to simulate ALS resistance and to better evaluate preemergence Nortron efficacy on kochia. Nortron was applied preemergence on April. The standard rate program included three applications, with the first applied to full cotyledon sugar beets on April 6, the second to two- to fourleaf sugar beets on May, and the third application to six- to eight-leaf sugar beets on May 4. Progress (ethofumesate + phenmedipham + desmedipham) was applied at 4.0, 5.4, and 6.7 oz ai/acre in the first, second, and third applications, respectively. UpBeet was applied at oz ai/acre in all three applications (excluding treatments where UpBeet was omitted). Stinger (clopyralid) was applied in the second and third applications at.5 oz ai/acre. The micro-rate program consisted of four applications with the first applied to cotyledon sugar beets on April, the second to cotyledon to sugar beets on April 0, the third application was inadvertently delayed and was applied to 8- to Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 94-98

79 0-leaf sugar beets on May 5, and the fourth to 8- to sugar beets on May 0. In the microrate program, Progress was applied at. oz ai/acre in the first two applications and at.0 oz ai/acre in the last two applications. All four micro-rate applications included UpBeet at 0.08 oz ai/acre (excluding treatments where UpBeet was omitted), Stinger at 0.5 oz ai/acre, and a methylated seed oil (MSO) at.5 percent v/v. Sugar beet injury was evaluated May 0 and June 9 and weed control was evaluated September. Sugar beet yields were determined by harvesting the center two rows of each plot on October 8 and 9. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Syngenta Seeds Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion Postemergence herbicides were very effective this year. Kochia control was greater than 98 percent with either the standard rate or micro-rate treatments containing UpBeet regardless of whether preemergence Nortron was applied (Table ). Removing UpBeet from the standard rate and the micro-rate resulted in a respective 8 and 58 percent decrease in kochia control on July 7. For the standard rate treatments without UpBeet, the addition of Nortron at any rate provided kochia control similar to the standard rate with UpBeet. For micro-rate treatments without UpBeet, the addition of preemergence Nortron, regardless of the rate, did not control kochia as well as the micro-rate with UpBeet. Increasing Nortron rates increased kochia control. Pigweed control also was reduced when UpBeet was omitted from the micro-rate. The addition of Nortron at 6 or 4 oz ai/acre improved kochia control, but the - or 48- oz ai/acre rates were required to control kochia equal to the microrate with UpBeet. There were no differences among treatments for common lambsquarters, hairy nightshade, or barnyardgrass control. Common lambsquarters and hairy nightshade control was 98 percent or higher while barnyardgrass control ranged from 87 to 99 percent. Injury on May 0 was significantly higher for standard rate treatments with UpBeet compared to standard rate treatments without UpBeet or compared to any of the micro-rate treatments (Table ). Within the micro-rate treatments, the 48- oz ai/acre rate of Nortron caused greater injury ( vs 5-4 percent) than any of the other micro-rate treatments with or without Nortron preemergence. On June 9, injury was similar among all treatments. Sugar beet yields were not significantly different among any of the standard rate treatments. Sugar beet yields were lowest with the micro-rate applied without UpBeet. The addition of preemergence Nortron at oz ai/acre to the micro-rate without UpBeet was the only treatment that produced yields similar to the micro-rate with UpBeet. The lower Nortron rates had lower yields and the 48- oz ai/acre Nortron treatment also yielded less than the micro-rate with UpBeet. The lower yield with the high rate of Nortron may have been related to the increased sugar beet injury. In areas where kochia has become resistant to UpBeet, a preemergence application of Nortron followed by postemergence herbicides at standard rates should provide effective control. Removing UpBeet from the spray mixture may not be advisable since UpBeet would still be effective in controlling non-upbeet-resistant kochia and also helps control other weeds. The micro-rate should Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 94-98

80 not be used in areas with UpBeet resistant kochia because even with high rates of preemergence Nortron, acceptable kochia control cannot be achieved. Table. Kochia control with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Weed control Pigweed Lambs- Hairy Barnyardgrass Kochia spp. quarters nightshade Treatment* Rate Timing oz ai/acre & % v/v % Untreated control Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Micro-Rate Program Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron fb Standard with Upbeet Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet % v/v % v/v ,4 7,8,5,6,5,6,5,6,5,6,5,6,5,6,4,7,8,4,7, ,4,7,8,4,7,8,4,7, Standard w/out UpBeet ---,5, Micro w/out UpBeet ---,4,7, Nortron fb Micro w/out UpBeet ,4,7, LSD ( 0.05) NS NS NS *fb = Followed by. Application timings were () April preemergence, () April to cotyledon beets, () April 6 to full cotyledon beets, (4) April 0 to beets, (5) May to - to beets, (6) May 4 to 6- to 8-leaf beets, (7) May 5 to 8- to 0-leaf beets, and (8) May 0 to 8- to beets. Pigweed species included Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 94-98

81 Table. Sugar beet injury and yield with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Sugar beet Injury Yield Root Treatment* Rate Timing yield Sucrose Extraction ERS % % oz ai/acre and % v/v --- ton/acre - lbs/acre Untreated control ,958 Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Micro-Rate Program Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard with UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Standard w/out UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro with UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet Nortron fb Micro w/out UpBeet % v/v % v/v ,80,4 7, ,64,5,6,5,6,5,6,5,6,5,6,5,6,4,7,8,4,7, , , , , , , , , ,98,4,7,8,4,7,8,4,7, , , ,00 Standard w/out UpBeet ---,5, ,45 Micro w/out UpBeet ---,4,7, ,786 Nortron fb Micro w/out UpBeet ,4,7, ,490 LSD (0.05) NS,97 *fb = Followed by Application timings were () April preemergence, () April to cotyledon beets, () April 6 to full cotyledon beets, (4) April 0 to beets, (5) May to to beets, (6) May 4 to 6 to 8-leaf beets, (7) May 5 to 8 to 0-leaf beets, and (8) May 0 to 8 to beets. Sugar beets were harvested October 8 and 9. ERS = estimated recoverable sucrose. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 94-98

82 TIMING OF DUAL MAGNUM AND OUTLOOK APPLICATIONS FOR WEED CONTROL IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 004 Introduction Outlook (dimethenamid-p) and Dual Magnum (s-metolachlor) are soil-active herbicides that are labeled for postemergence application in sugar beet. They can be applied to two-leaf or larger beets. Outlook or Dual Magnum was applied at different timings as part of a standard rate herbicide program. The objectives of this trial were to ) determine if weed control can be improved with Outlook or Dual Magnum in the standard rate program, and ) determine if the application timing of these herbicides influences weed control or crop response. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 8, 004. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April 9, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May 0 to. Plots were sidedressed on June with 75 lb nitrogen (N) (urea), 0 lb potash (K O), 5 lb sulfates (SO 4 ), 8 lb elemental sulfur (S), lb manganese (Mn), lb zinc (Zn), and lb/acre boron (B). All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On May 6, Temik 5G (4 lb prod/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 5, Topsin M (0 oz prod/acre) plus S at 6 lb/acre, phosphate (P O 5 ) at.5 lb/acre, and Zn at 0. lb/acre were applied on August 4, and Headline ( fl oz/acre) plus S at 6 lb/acre were applied on August 8. All fungicide treatments were applied by air. Herbicide treatments were broadcast applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were 4 rows wide and 7 ft long and treatments were arranged in a randomized complete block design with 4 replicates. Outlook, Dual Magnum, and Treflan were applied at various timings as part of a standard rate herbicide program to evaluate the effect of application timing on weed control and crop response. The standard rate program consisted of Progress applied at 4.0, 5.4, and 6.7 oz ai/acre in the first, second, and third applications, respectively. UpBeet was applied at oz ai/acre in all three applications and Stinger at.5 oz ai/acre in the last two applications. Dual Magnum was applied preemergence only, or in the second or third postemergence application, or preemergence and in the second application, or in the second and third applications. Outlook was applied in the second or third applications. Both Dual Magnum and Outlook were applied in combination with Treflan in the second postemergence application. The preemergence treatments were applied April. The first, second, and third postemergence applications were made on April 6, May, and May 4, to cotyledon, - to, and 6- to 0-leaf beets, respectively. Sugar beet injury was evaluated on May 0 and June 9 and weed control was evaluated on September. Sugar beet yields were determined by harvesting the center two rows of each plot on October 8 and 9. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 99-0

83 was taken from each plot for quality analysis. The samples were coded and sent to Syngenta Seeds Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion The addition of Outlook or Dual Magnum or combinations of Outlook or Dual Magnum with Treflan improved barnyardgrass control compared to the standard postemergence treatment alone (Table ). For all other weeds, control was similar among treatments. There also were no differences in sugar beet injury (Table ) or sugar beet stand (data not shown) among treatments. All herbicide treatments had greater yields compared to the untreated control, but yields did not differ among herbicide treatments. This research suggests that both Dual Magnum and Outlook can be applied in combination with standard rate herbicides in sugar beets without significant sugar beet injury. No injury was observed with preemergence applications of Dual Magnum in this trial. However, in other sugar beet production regions, under extremely wet conditions, Dual Magnum has caused sugar beet injury when applied preemergence. In 004, weather conditions were favorable and maximized the weed control provided by postemergence herbicide treatments. Under different environmental conditions, Dual Magnum or Outlook may have provided increased levels of broadleaf weed control. Besides helping control annual weeds, both Dual Magnum and Outlook are effective in suppressing yellow nutsedge in sugar beet. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 99-0

84 Table. Weed control in sugar beet with standard rate herbicide treatments including postemergence applications of Outlook and Dual Magnum, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Pigweed Weed control Lambs- Hairy Treatment Rate Timing* Kochia Spp. quarters nghtshade oz ai/acre % Untreated control Progress + UpBeet + Dual Magnum Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger + Dual Magnum Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Outlook + Treflan Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Outlook Progress + UpBeet Progrees + UpBeet + Stinger + Dual Magnum + Treflan Progress + UpBeet + Stinger Barnyardgrass LSD (0.05) NS NS NS NS 6 *Application timings were () April, () April 6 to cotyledon beets, () May to - to beets, and () May 4 to 6- to 0-leaf beets. Weed control was evaluated October 8 and 9. Pigweed species included Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 99-0

85 Table. Sugar beet injury and yield with standard rate herbicide treatments including postemergence applications of Outlook and Dual Magnum, Malheur Experiment Station, Oregon State University, Ontario, OR, 004. Sugar beet Injury Yield Root Treatment Rate Timing* yield Sucrose Extraction ERS oz ai/acre % ton/acre % lbs/acre Untreated control ,90 Progress + UpBeet + Dual Magnum Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger ,09 Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger + Dual Magnum Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Outlook + Treflan Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger , , , , , , , , ,06 Outlook Progress + UpBeet Progrees + UpBeet + Stinger + Dual Magnum + Treflan ,97 Progress + UpBeet + Stinger LSD (0.05) -- NS NS 6.6 NS NS,8 *Application timings were () April, () April 6 to cotyledon beets, () May to - to beets, and () May 4 to 6- to 0-leaf beets. Sugar beets were harvested on October 8 and 9. ERS = estimated recoverable sucrose Malheur Experiment Station Annual Report 004. Oregon State University. Special Report 06. Pg 99-0

86 WEED CONTROL AND CROP RESPONSE WITH OPTION HERBICIDE APPLIED IN FIELD CORN Corey V. Ransom, Charles A. Rice and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Weed control is important in field corn production to reduce competition with the current crop and to prevent the production of weed seed for future crops. Field trials were conducted to evaluate Option (foramsulfuron) herbicide applied alone and in various combinations for weed control and crop tolerance in furrow-irrigated field corn. Option is a new postemergence sulfonylurea herbicide that controls annual and perennial grass and broadleaf weeds in field corn. Option contains a safener that is intended to enhance the ability of corn to recover from any yellowing or stunting, which may be associated with the application of sulfonylurea herbicides. Materials and Methods Roundup UltraMax was applied preplant at 0.56 lb ae/acre to control volunteer wheat on May. Pioneer variety 'P-6N8' Roundup Ready (0-day relative maturity) field corn was planted with a John Deere model 7 Flexi Planter on May, 00. Seed spacing was one seed every 7 inches on 0-inch rows. Plots were 0 by 0 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Plots were sidedressed with lbs N, 48 lbs phosphate, 6 lbs potash, lbs sulfates, lb Zn and B, lbs Mn, and 0 lbs elemental S/acre on May 4. Herbicide treatments were applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Crop response and weed control were evaluated throughout the growing season. Crop height measurements were taken to evaluate herbicide injury. Height values were determined by measuring the distance from the ground to the first collar for 0 plants from the center two rows in each plot. Corn yields were determined by harvesting ears from 5-ft sections of the center two rows in each four-row plot on October 7. The harvested ears were shelled and grain weight and percent moisture content were recorded. Grain yields were adjusted to percent moisture content. Data were analyzed using analysis of variance (ANOVA) and treatment means were separated using Fisher's protected least significant difference (LSD) at the 5 percent level (P = 0.05) for weed control and injury data and at the 0 percent level (P = 0.0) for corn yield data. Option herbicide was applied early postemergence (EP) to corn at the V growth stage at rates of 0.08 and 0.08 lb ai/acre. The label rate for Option is 0.08 lb ai/acre when susceptible weeds are at or below the maximum size as stipulated by the label. The higher rate of 0.08 lb ai/acre is intended for use as a rescue treatment on weeds that are above labeled size. Option (0.08 lb ai/acre) was also evaluated in EP combinations with Distinct (dicamba + diflufenzopyr), Callisto (mesotrione), Aatrex (atrazine), or Outlook (dimethenamid-p) herbicides. In addition, Option was applied EP following a preemergence () application of Topnotch (acetochlor). Comparison treatments included EP combinations of Clarion (nicosulfuron + rimsulfuron) plus Distinct, Accent (nicosulfuron) plus Distinct, Roundup UltraMax (glyphosate) applied EP followed by a second application at a late postemergence (LP) timing, and finally Topnotch applied followed by an EP application of Roundup UltraMax. All postemergence Option applications included a methylated seed oil (MSO) at.0 percent v/v and percent nitrogen at.5 percent v/v. In treatments where Distinct Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -5

87 was applied postemergence without Option, a non-ionic surfactant (NIS) at 0.5 percent v/v and percent nitrogen at.5 percent v/v were included. Results and Discussion Control of pigweed species (i.e., Powell amaranth and redroot pigweed) from herbicide treatments ranged from 95 to 00 percent on July 8 and was similar among herbicide treatments (Table ). Option applied alone at either 0.08 or 0.08 lb ai/acre and when applied with Outlook provided 86 percent or less common lambsquarters control, which was significantly less than all other treatments on July 8. Option applied postemergence with Distinct, Callisto, or Aatrex or following a preemergence application of Topnotch gave 98 percent or greater common lambsquarters control when evaluated on July 8. Common lambsquarters control with postemergence Option was improved when preceded by a preemergence application of Topnotch. Hairy nightshade control was 94 percent or greater with all herbicide treatments. The only differences were with postemergence combinations of Clarion and Distinct or Accent and Distinct, which gave less hairy nightshade control than treatments with preemergence Topnotch applications, two postemergence applications of Roundup UltraMax, or when Option was applied with Callisto. Option applied postemergence with Distinct, Callisto, or Aatrex provided greater kochia control than when Option was applied alone or with Outlook. The postemergence combination of Option plus Distinct provided percent greater barnyardgrass control than did the treatment of Accent plus Distinct. Barnyardgrass control with postemergence Option was improved when preceded by a preemergence application of Topnotch. The combination of Clarion and Distinct provided broadleaf weed control similar to Option and Distinct. Weed control was similar with Option alone regardless of rate. Both treatments incorporating Roundup UltraMax provided greater than 98 percent control of all weeds. Weed control results from this trial suggest that Option should be applied postemergence in combination with or following a preemergence application of another herbicide in order to provide broad spectrum weed control in field corn. In terms of broad spectrum weed control, applying Option postemergence with Distinct or Aatrex or following preemergence Topnotch were some of the better combinations with Option. Corn injury on June 4, 7 days after the EP applications, ranged from 0 to 0 percent (Table ). No injury, as compared to the untreated control, was observed with the postemergence combination of Accent plus Distinct, or treatments including Roundup UltraMax, for which only the EP and applications had been applied by June 4. Injury was greatest with treatments containing Option. Injury with these treatments was characterized by slight stunting due to shortened internodes and slight yellowing of the foliage compared to the untreated control. Plant height data collected on June 6 showed measurable corn stunting associated with postemergence combinations of Option plus Distinct and Option plus Outlook when compared to the untreated control. Injury on June, 4 days after EP applications, was greatest with the treatment of Option plus Outlook. Injury with this treatment was greater than from all other treatments except for those where Option was combined with Distinct or Callisto. The yellowing that was observed previously was no longer visible on June. However, stunting was still visible in certain plots where Option had been applied. Corn injury was no longer detectable by June 0 and no further injury evaluations were taken. Corn yields ranged from a low of 66 bu/acre with the untreated control to a high of 85 bu/acre with two applications of Roundup UltraMax (Table ). Corn yields in this trial were significantly less than those typically obtained at the Malheur Experiment Station. This trial was established approximately - weeks later than what is typical for corn trials on station. Optimum conditions were not present Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -5

88 during pollination and the ears did not fully fill. Reduced yield may be attributed to extremely hot daytime temperatures (>00 F) and low relative humidity during pollen shed and silking, resulting in poor kernel set. The only treatments to yield significantly (P = 0.0) greater than the untreated control were those including Roundup UltraMax, combinations of Clarion plus Distinct, or Accent plus Distinct. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -5

89 Table. Weed control with Option herbicide applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed C. lambsquarters H. night- Barnyardspp shade Kochia grass Treatment Rate Timing* lb ai/acre % v/v % Option + MSO + % N % +.5% EP c 98 ab de Option + MSO + % N % +.5% EP 97 8 c 98 ab 90 9 cde Option + Distinct + MSO + % N % +.5% EP ab 99 ab a-d Option + Callisto + MSO + % N % +.5% EP ab 00 ab de Option + Aatrex + MSO + % N % +.5% EP a 00 a b-e Option + Outlook + MSO + % N % +.5% EP c 98 ab 9 96 a-e Clarion + Distinct + NIS + % N % +.5% EP b 94 b 95 9 de Accent +Distinct + NIS + % N % +.5% EP ab 94 b e Topnotch ab 00 a abc Option + MSO + % N % +.5% EP Topnotch ab 00 a a Roundup UltraMax 0.56 LP Roundup UltraMax 0.56 EP ab 00 a ab Roundup UltraMax 0.56 LP LSD (0.05) NS *Application timings were preemergence () on 5--0, early postemergence (EP) applied to corn at the V growth stage on 6-7-0, and late postemergence (LP) to corn at the V to V4 growth stages on Pigweed species were a mixture of Powell amaranth and redroot pigweed. The ANOVA was performed on arcsine square root percent transformed data. Mean separations are applied to nontransformed data. Within-column values followed by the same letter designation are similar (P = 0.05). The untreated control was not included in the ANOVA for weed control. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -5

90 Table. Injury and yield with Option herbicide applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Field Corn Injury Height Yield Treatment Rate Timing* lb ai/acre % v/v % Inches bu/acre Untreated control Option + MSO + % N % +.5% EP Option + MSO + % N % +.5% EP Option + Distinct + MSO + % N % +.5% EP Option + Callisto + MSO + % N % +.5% EP Option + Aatrex + MSO + % N % +.5% EP Option + Outlook + MSO + % N % +.5% EP Clarion + Distinct + NIS + % N % +.5% EP Accent + Distinct + NIS + % N % +.5% EP Topnotch.0 EP Option + MSO + % N % +.5% Topnotch Roundup UltraMax 0.56 LP Roundup UltraMax 0.56 EP Roundup UltraMax 0.56 LP LSD (0.05) NS LSD (0.0) *Application timings were preemergence () on 5--0, early postemergence (EP) applied to corn at the V growth stage on 6-7-0, and late postemergence (LP) to corn at the V to V4 growth stages on The untreated control was not included in the ANOVA for percent injury. Height was determined by measuring the distance from the soil surface to the first collar. Corn yields were significantly less than those typically obtained at the Malheur Experiment Station. Reduced yield may be attributed to extremely hot daytime temperatures (>00 F) and low relative humidity during pollen shed and silking resulting in poor kernel set. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -5

91 EMERGENCE HERBICIDES FOR WEED CONTROL IN ONION Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Weed control is essential for the production of marketable onions. Only a few herbicides are registered for preemergence application in onion. Effective preemergence herbicides can control weeds as they germinate and reduce the size and number of weeds that are present when onions are large enough to tolerate postemergence herbicide applications. This research evaluated registered and experimental herbicides for preemergence weed control in onion. Methods General Procedures Trials were conducted at the Malheur Experiment Station under furrow irrigation. On March 8, onions (cv. 'Vaquero', Sunseeds, Parma, ID) were planted at a.7-inch spacing in double rows on -inch beds. Plots were four rows wide and 7 ft long and arranged in a randomized complete block design with four replicates. Lorsban was applied in a 6-inch band over each row at.7 oz/,000 ft of row. Onions were sidedressed with 7 lb N, 7 lb P, lb Sulfate, 4 lb S, 6 lb Zn, and lb B/acre on June. Registered insecticides and fungicides were applied for thrips and downy mildew control. Herbicide treatments were applied with a CO -pressurized backpack sprayer. Preemergence applications were applied at 0 gal/acre at 0 psi and postemergence treatments were applied at 40 gal/acre at 0 psi. All plots received Poast (sethoxydim) at 0.9 lb ai/acre plus crop oil concentrate (COC) (.0% v/v) applied postemergence at 0 gal/acre and 0 psi on June 6. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 7 and 8 and graded by size on September -5.Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Preemergence Dacthal and Prowl Preemergence-applied Prowl (pendimethalin) was compared to Dacthal (DCPA) 75 WP (a dry formulation) and Dacthal 6F (a liquid formulation). Combinations of Prowl plus Dacthal in two different ratios were also compared. Postemergence applications following preemergence Prowl and Dacthal combinations were similar with the exception of a comparison of Buctril (bromoxynil) plus (oxyflurofen) to Buctril plus Valor (flumioxazin) applied to two-leaf onions. Comparison of Preemergence Prowl, Nortron, and Outlook Preemergence applications of Prowl, Nortron (ethofumesate), and Outlook (dimethenamid-p) in combination with Roundup (glyphosate) were evaluated for weed control and onion tolerance. Each product was evaluated at two rates. Combinations of Prowl with Nortron or Outlook were also Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

92 evaluated. Preemergence treatments with soil-active herbicides were compared to plots where only Roundup was applied preemergence. Results and Discussion Preemergence Dacthal and Prowl Preemergence Prowl gave greater than 89 percent control of all weed species and was more effective on nightshade than Dacthal alone (Table ). There were no differences in weed control efficacy between the two Dacthal formulations. Certain combinations of Prowl plus Dacthal increased pigweed control compared to Dacthal alone but were not more effective than Prowl alone. Plots treated with Dacthal alone had reduced colossal, super colossal, and marketable onion yields compared to plots treated with Prowl alone or in combination with Dacthal (Table ). The reduced yields were caused by weed competition. Comparison of Preemergence Prowl, Nortron, and Outlook Preemergence treatments were effective because of timely rain. No onion injury was observed from preemergence treatments (Table ). Preemergence Prowl was most effective in controlling pigweed and hairy nightshade compared to Outlook or Nortron. Prowl significantly improved common lambsquarters control compared to Roundup alone. High rates of Outlook and Nortron gave lambsquarters control similar to Prowl but were not greater than Roundup alone or lower rates of Outlook or Nortron. Outlook did not increase hairy nightshade control compared to Roundup alone. Nortron increased nightshade control percent and Prowl increased control 75-8 percent compared to Roundup alone. In past trials at the Malheur Experiment Station, Prowl has been much weaker on hairy nightshade. Preemergence Outlook did not increase marketable onion yields compared to Roundup alone (Table 4). In general, both Nortron and Prowl increased marketable onion yields compared to Outlook or Roundup alone. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

93 Table. Onion injury and weed control in response to preemergence Dacthal and Prowl and different postemergence herbicide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Injury Pigweed lambsquarters Common Hairy nightshade Treatment Rate Timing* lb ai/acre Leaf % Untreated Roundup + Prowl Roundup + Dacthal 75 WP Roundup + Dacthal 6F Roundup + Prowl + Dacthal Roundup + Prowl + Dacthal Roundup + Prowl + Dacthal Buctril + Valor Roundup + Prowl + Dacthal Buctril + Valor LSD (0.05) NS *Preemergence () treatment applied on April, two-leaf () on May 6, three-leaf () on May 7, and fourleaf () on June 9. Pigweed is a combination of redroot pigweed and Powell amaranth Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

94 Table. Onion yield in response to preemergence Dacthal and Prowl and different postemergence herbicide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Roundup + Prowl Roundup + Dacthal 75 WP Roundup + Dacthal 6F Roundup + Prowl + Dacthal Roundup + Prowl + Dacthal Roundup + Prowl + Dacthal Buctril + Valor Roundup + Prowl + Dacthal Buctril + Valor LSD (0.05) *Preemergence () treatment applied on April, two-leaf () on May 6, three-leaf () on May 7, and fourleaf () on June 9. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

95 Table. Onion injury and weed control in response to preemergence Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Injury Pigweed lambsquarters Common Hairy nightshade Treatment Rate Timing* lb ai/acre Leaf % Untreated Roundup Roundup + Outlook POST Program same Roundup + Outlook POST Program same Roundup + Nortron POST Program same Roundup + Nortron POST Program same Roundup + Prowl POST Program same Roundup + Prowl POST Program same Roundup + Prowl + Nortron POST Program same Roundup + Prowl + Outlook POST Program same LSD (0.05) NS *Preemergence () treatment applied on April, two-leaf () on May 6, three-leaf () on May 7, and fourleaf () on June 9. Pigweed is a combination of redroot pigweed and Powell amaranth. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

96 Table 4. Onion yield in response to preemergence Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Roundup Roundup + Outlook POST Program same Roundup + Outlook POST Program same Roundup + Nortron POST Program same Roundup + Nortron POST Program same Roundup + Prowl POST Program same Roundup + Prowl POST Program same Roundup + Prowl + Nortron POST Program same Roundup + Prowl + Outlook POST Program same,, 4- leaf LSD (0.05) *Preemergence () treatment applied on April, two-leaf () on May 6, three-leaf () on May 7, and four-leaf () on June 9. The information in this report is for the purpose of informing cooperators in industry, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any pesticide. Pesticide labels should always be consulted before any pesticide use. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 9-96

97 DUAL MAGNUM APPLICATIONS FOR WEED CONTROL IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Dual Magnum (s-metolachlor) was labeled in the spring of 00 for pre-plant incorporated (PPI), preemergence (), and postemergence (POST) applications to sugar beet. Presently, because of injury from PPI and applications to sugar beet this past season in the Red River Valley of North Dakota and Minnesota, the future label status of these application methods is uncertain. The objective of this trial was to evaluate weed control and crop response with PPI,, and POST Dual Magnum applications in sugar beet. Methods This trial was conducted in a furrow-irrigated field near Nampa, Idaho. Dual Magnum was applied PPI,, or POST to two-leaf beets at.7 or.59 lb ai/acre. Nortron (ethofumesate) was applied PPI and at.6 lb ai/acre for comparison. Herbicide treatments were broadcast-applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. PPI,, and POST treatments were applied on April 7, April 9, and May, respectively. PPI treatments were incorporated immediately after application with an Alloway field cultivator equipped with s-tines and rolling baskets. Sugar beets were planted following incorporation. The timing of the applications was not ideal as approximately 0 percent of the sugar beets had already begun to emerge. A standard rate herbicide program consisting of three POST applications of Progress (ethofumesate + desmedipham + phenmedipham), UpBeet (triflusulfuron), and Stinger (clopyralid) was broadcast over the entire experimental area independent of Dual Magnum and Nortron applications. Sugar beet injury and weed control were evaluated throughout the season. Sugar beet stand populations/0 ft of row were recorded on May following PPI and applications. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The trial was not harvested. Results and Discussion Sugar beet stand populations on May ranged from to 6 plants/0 ft of row and were not different among treatments (Table ). Sugar beet injury on May was greatest with the treatments. This injury was most likely enhanced because the treatments were applied late and approximately 0 percent of the beets were beginning to emerge, allowing for direct herbicide contact. Sugar beet injury with Nortron was less than with Dual Magnum applied at.59 lb ai/acre on May and June and when applied at.7 lb ai/acre on June. Injury was not different between the PPI treatments and the standard rate program alone. There were no differences in weed control among the PPI treatments (Table ). The treatments gave similar control of all evaluated weed species. Redroot pigweed control was less with POST Dual Magnum applications than with PPI or treatments of Dual Magnum or Nortron. POST applications of Dual Magnum were applied after many of the weeds had emerged and therefore they were considerably less effective. POST Dual Magnum at either application rate did not improve control of the evaluated weeds when compared to the standard rate alone. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -

98 Control of kochia, hairy nightshade, and common lambsquarters were similar with Dual Magnum applied POST at.59 lb ai/acre and with all treatments. However, when Dual Magnum was applied POST at.7 lb ai/acre, control of these weeds was less than with the treatments. Similar control of kochia, hairy nightshade, and common lambsquarters was achieved with all PPI and treatments. Table. Weed control and crop response with Dual Magnum applications in sugar beet, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Weed control Redroot Hairy C. Lambsquarters Stand Injury pigweed Kochia nightshade Treatment* Rate Timing lb ai/acre No./0 ft % % Standard rate w/out soil-active b 9 c 6 Nortron.6 PPI ab 98 ab 95 Dual Magnum.7 PPI a 89 a 99 Dual Magnum.59 PPI ab 9 a 99 Nortron a 00 ab 98 Dual Magnum a 00 a 96 Dual Magnum a 00 a 99 Dual Magnum.7 POST b 80 c 6 Dual Magnum.59 POST ab 88 bc 74 LSD (0.05) NS *A standard rate herbicide program was blanketed over the entire plot area independent of Dual Magnum and Nortron applications. PPI applications were made on April 7, on April 9, and POST on May, 00. treatments were applied when approximately 0 percent of the sugar beets had just emerged and most likely increased injury with these treatments. POST treatments had not yet been applied at the May evaluation. In columns where letter designations appear the ANOVA was performed on arcsine square root percent transformed data. Mean separations were applied to non-transformed data. Values with the same letter designations are similar (P = 0.05). Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg -

99 EVALUATION OF PROGRESS AND BETAMIX FORMULATIONS FOR WEED CONTROL AND SUGAR BEET RESPONSE Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Pressure from the U.S. Environmental Protection Agency to remove the carrier isophorone from the current formulations of Betamix (desmedipham + phenmedipham) and Progress (ethofumesate + desmedipham + phenmedipham) herbicides has lead Bayer CropScience to develop formulations of these products that use oilbased carriers. The objective of this trial was to determine if sugar beet tolerance and weed control efficacy with the experimental oil-based formulations of Progress (AE B0499) and Betamix (AE B08584) are similar to their respective commercial formulations. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 4, 00. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April, weed seed was spread over the entire experimental area to promote an even weed distribution. After planting the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May and 4. Plots were sidedressed on June with 76 lb nitrogen (urea), 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre boron. All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On May6, Temik 5G (4 lb/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 7 and again on July with Super Six liquid sulfur (6 pt/acre). Topsin M (0.5 lb/acre) was applied on August 4. All fungicide treatments were applied by air. Herbicide treatments were broadcast-applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. Experimental and commercial formulations of Progress and Betamix were applied alone at 4.0 oz ai/acre and in a micro-rate at.8 and.56 oz ai/acre with UpBeet (triflusulfuron) at 0.06 oz ai/acre, Stinger (clopyralid) at 0.5 oz ai/acre, and Scoil (methylated seed oil) at.5 percent v/v. The experimental and commercial formulations were applied three times alone with the first application to cotyledon beets, the second to two-leaf beets, and the third to six-leaf beets. The three application dates were April, May, and May. The microrate treatments were applied four times with applications to cotyledon beets on April, two-leaf beets on April 9, four-leaf beets on May 4, and six-leaf beets on May. Sugar beet injury and weed control were evaluated throughout the season. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-

100 using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion In general, weed control was less with the experimental and commercial Progress and Betamix herbicides applied alone at standard rates compared with the micro-rate treatments (Table ). On June 6, the experimental formulations, compared with their commercial equivalents, provided similar control of nightshade, common lambsquarters, and kochia. The only difference was observed with the experimental Progress formulation, which controlled pigweed less than its commercial formulation on June 6. Sugar beet injury ranged from to percent on May 5 prior to the last herbicide application for both the micro and standard rate programs (Table ). On June ( days after treatment), sugar beet injury had decreased with most treatments and was similar between the experimental and commercial formulations, whether applied alone at standard rates or in the micro-rate program. Sugar beet root and estimated recoverable sucrose yields were not different when comparing the experimental formulations with their respective commercial formulations applied alone at standard rates or as part of the micro-rate program (Table ). There were no differences in percent sucrose or percent extraction among any of the treatments. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-

101 Table. Weed control with experimental and commercial Progress and Betamix formulations, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed spp Nightshade Lambsquarters Kochia Treatment* Rate Timing oz ai/acre % Exp. Progress Exp. Progress Exp. Progress Progress Progress Progress Exp. Progress + UpBeet + Stinger + MSO Exp. Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Exp. Betamix Exp. Betamix Exp. Betamix Betamix Betamix Betamix Exp. Betamix + UpBeet + Stinger + MSO Exp. Betamix + UpBeet + Stinger + MSO Betamix + UpBeet + Stinger + MSO Betamix + UpBeet + Stinger + MSO % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v 4 6, 5, 6, 5, , 5, 6, 5, Untreated control LSD (0.05) 4 8 NS 5 8 *Experimental Progress (AE B0499) and Betamix (AE B08584) formulations are oil-based. Applications were made () April 9 to cotyledon beets, () April to full cotyledon beets, () April 6 to cotyledon to beets, (4) April 0 to beets, (5) May to beets, and (6) May to 8-leaf beets. Pigweed species included Powell amaranth and redroot pigweed. The untreated control was not included in the weed control analysis. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-

102 Table. Sugar beet injury and yield with experimental and commercial Progress and Betamix formulations, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Injury Yield Treatment Rate Timing* Root yield Sucrose Extraction ERS oz ai/acre % ton/acre % lb/acre Exp. Progress Exp. Progress Exp. Progress ,97 Progress Progress Progress Exp. Progress + UpBeet + Stinger + MSO Exp. Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Exp. Betamix Exp. Betamix Exp. Betamix Betamix Betamix Betamix Exp. Betamix + UpBeet + Stinger + MSO Exp. Betamix + UpBeet + Stinger + MSO Betamix + UpBeet + Stinger + MSO Betamix + UpBeet + Stinger + MSO % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v 4 6, 5, 6, 5, , 5, 6, 5, , , , , , , ,56 Untreated control ,878 LSD (0.05) NS NS,49 *Applications were made () April 9 to cotyledon beets, () April to full cotyledon beets, () April 6 to cotyledon to beets, (4) April 0 to beets, (5) May to beets, and (6) May to 8-leaf beets. The untreated control was not included in the sugar beet injury analysis. Sugar beets were harvested on October 7-8, 00. ERS = Estimated recoverable sucrose. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-

103 INFLUENCE OF SOIL-ACTIVE HERBICIDES ON WEED CONTROL WITH MICRO- RATE HERBICIDE PROGRAMS IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Trials were initiated to examine weed control and crop response associated with soil-active herbicides applied postemergence as part of a three- or four-application micro-rate program. The soil-active herbicides evaluated were Outlook (dimethenamid-p), Dual Magnum (s-metolachlor), and Nortron (ethofumesate). Nortron can be applied pre-plant incorporated (PPI), preemergence (), or postemergence (POST) in sugar beet. Outlook is labeled in sugar beet for POST applications only to two-leaf or larger beets. Dual Magnum received a sugar beet label in 00 for PPI,, and POST applications but due to injury concerns the future status of PPI and applications are uncertain. This trial was established at the Malheur Experiment Station under furrow irrigation on April 4, 00. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April, kochia, pigweed, and hairy nightshade seed was spread over the entire experimental area to promote an even weed distribution. After planting, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May. Plots were sidedressed on June with 76 lb nitrogen (urea), 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre boron. All plots were treated with Roundup (0.75 lb ai/acre) prior to sugar beet emergence on April. On May 6, Temik 5G (4 lb/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 7 and again on July with Super Six liquid sulfur (6 pt/acre) and Topsin M (0.5 lb prod/acre) was applied on August 4. All fungicide treatments were applied by air. Herbicide treatments were broadcast-applied with a CO-pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. Micro-rate treatments were applied three or four times. Dual Magnum ( oz ai/acre), Nortron (6 oz ai/acre), or Outlook (0 oz ai/acre) were applied in the second application to provide residual control of later germinating weeds. All treatments were compared to the micro-rate applied three or four times and to a standard herbicide treatment applied three times. Micro-rate and standard rate treatments were applied broadcast. Microrate treatments contained Progress (. oz ai/acre), UpBeet (0.06 oz ai/acre), Stinger (0.5 oz ai/acre), Select (0.5 oz ai/acre), and a methylated seed oil (MSO) at.5 percent v/v. Micro-rate applications were made on April 9, April 0, May, and May. The standard rate applications were made on April 6, May, and May. The micro-rate treatments were initiated when sugar beets were in the cotyledon stage. The standard rate treatment was initiated when the cotyledons were fully expanded and the first true leaves had emerged. Sugar beet injury and weed control were evaluated throughout the season. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-05

104 purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion Pigweed control on June 0 (5 days after treatment [DAT]) was greater with three applications of the microrate with Outlook or Dual Magnum in the second application versus the micro-rate applied four times (Table ). The addition of Outlook or Dual Magnum to the micro-rate applied three times increased pigweed control by 6 percent. Nortron did not significantly improve pigweed control when added to the micro-rate applied either three or four times. Pigweed control was similar among all treatments where the micro-rate was applied four times or when Outlook, Dual Magnum, or Nortron were added to the micro-rate applied three times. There were no differences in control among treatments for common lambsquarters or hairy nightshade. The addition of Outlook or Dual Magnum, but not Nortron, increased kochia control on July (70 DAT) compared to three applications of the micro-rate alone. Similar kochia control was obtained with the standard rate treatment, all four application treatments of the micro-rate, and when Outlook or Dual Magnum were included in the three application micro-rate treatment. All treatments provided 00 percent barnyardgrass control except the microrate applied three times or the micro-rate applied three times with either Dual Magnum or Nortron in the second application. Sugar beet injury on May 5 was greater in treatments with postemergence Outlook, Dual Magnum, or Nortron applications compared to the micro-rate treatments without these herbicides and the standard rate treatment (Table ). Micro-rate treatments where Nortron was applied injured sugar beets less than micro-rate treatments where Dual Magnum was applied. Sugar beet injury on June was similar among herbicide treatments. Sugar beet root yields were similar among herbicide treatments ranging from 46.7 to 49. tons/acre (Table ). Estimated recoverable sucrose yields ranged from,077 to 4,00 lbs/acre and were not different among herbicide treatments. All treatments had greater root and estimated recoverable sucrose yields than the untreated control. There were no differences in percent sucrose content or percent extraction among treatments. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-05

105 Table. Weed control with micro-rate herbicide treatments applied a different number of times and in various combinations in sugar beet, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed spp Weed control Weed control Weed control Weed control Hairy nightshade Kochia Kochia Treatment Rate Timing* Weed control Lambsquarters Barnyardgrass oz ai/acre % % % % % % Progress + Upbeet + Stinger + Select + MSO % v/v,,5, Progress + Upbeet + Stinger + Select + MSO % v/v,, Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Outlook Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Dual Magnum Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO +Nortron Progress + Upbeet + Stinger; Progress + Upbeet + Stinger + Select Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Outlook; Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Dual Magnum Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Nortron Progress + Upbeet + Stinger + Select + MSO % v/v % v/v % v/v % v/v % v/v; % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v,5,5,5,4 6,5 6,5 6, Untreated Control LSD (0.05) 6 5 NS NS 7 *Application timings were () April 9 to cotyledon beets () April to cotyledon beets () April 6 to cotyledon to beets (4) April 0 to beets (5) May to beets (6) May to 8-leaf beets. Pigweed species included Powell amaranth and redroot pigweed. The untreated control was not included in the weed control analysis. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-05

106 Table. Sugar beet injury and yield with micro-rate herbicide treatments applied a different number of times and in various combinations in sugar beet, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Treatment Rate Timing* Sugar beet Sugar beet Sugar beet Sugar beet Sugar beet Sugar beet Injury Injury Yield Yield Yield Yield Root Yield Sucrose Extraction ERS oz ai/acre % % ton/acre % % lb/acre Progress + Upbeet + Stinger + Select + MSO % v/v,,5, ,669 Progress + Upbeet + Stinger + Select + MSO % v/v,, ,077 Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Outlook Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Dual Magnum Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Nortron Progress + Upbeet + Stinger Progress + Upbeet + Stinger + Select Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Outlook Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Dual Magnum Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO Progress + Upbeet + Stinger + Select + MSO + Nortron Progress + Upbeet + Stinger + Select + MSO % v/v % v/v % v/v % v/v % v/v % v/v ; % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v,5,5,5;,4; 6,5 6,5 6, , , , , , , ,00 Untreated Control LSD (0.05) NS NS,60 *Application timings were: () April 9 to cotyledon beets () April to cotyledon beets () April 6 to cotyledon to beets (4) April 0 to beets (5) May to beets (6) May to 8-leaf beets. The untreated control was not included in the sugar beet injury analysis. Sugar beets were harvested on October 6-7, 00. ERS = Estimated recoverable sucrose Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 0-05

107 KOCHIA CONTROL WITH EMERGENCE NORTRON IN STANDARD AND MICRO-RATE HERBICIDE PROGRAMS Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction The distribution of kochia resistant to UpBeet (triflusulfuron) herbicide and other acetolactate synthase (ALS) inhibitors (i.e., sulfonylureas, imidazolinones, and triazolopyrimidines) has increased in recent years and poses a serious problem in sugar beet production, as none of the currently registered postemergence herbicides effectively control ALS-resistant kochia. In these trials, Nortron (ethofumesate) was evaluated for preemergence control of kochia in sugar beet. Nortron is a soil-active herbicide used preemergence or early postemergence to control annual grasses and broadleaf weeds. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 4, 00. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April, kochia seed was spread over the entire experimental area to promote an even weed distribution. After planting, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May and 4. Plots were sidedressed on June with 76 lb nitrogen (urea), 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre boron. All plots were treated with Roundup (0.75 lb ai/acre) on April prior to sugar beet emergence. On May6, Temik 5G (4 lb/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 7 and again on July with Super Six liquid sulfur (6 pt/acre). Topsin M (0.5 lb/acre) was applied on August 4. All fungicide treatments were applied by air. Herbicide treatments were broadcast applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. The treatments in this trial consisted of both standard and micro-rate postemergence weed control programs applied with or without a preemergence application of Nortron at either 6.0, 4.0, or.0 oz ai/acre with and without postemergence UpBeet. UpBeet was omitted from selected treatments to simulate ALS resistance and to better evaluate preemergence Nortron efficacy on kochia. Nortron was applied preemergence on April. The standard rate program included three applications with the first applied to full cotyledon sugar beets on April, the second to sugar beets on April 0, and the third application to 0-leaf sugar beets on May 6. Progress (ethofumesate + phenmedipham + desmedipham) was applied at 4.0, 5.4, and 6.75 oz ai/acre in the first, second, and third applications, respectively. UpBeet was applied at oz ai/acre in all three applications except those treatments where UpBeet was omitted. Stinger (clopyralid) was applied in the second and third applications at.5 oz ai/acre. The micro-rate program consisted of four applications with the first applied to cotyledon sugar beets on April 9, the second to cotyledon to sugar beets on April 6, the third applied to - to sugar beets on May, and the fourth to 0-leaf sugar beets on May 6. In the micro-rate program, Progress was applied at.8 oz ai/acre in the first two applications and at.0 oz ai/acre in the last two Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

108 applications. All four micro-rate applications included UpBeet at 0.08 oz ai/acre (excluding treatments where UpBeet was omitted), Stinger at 0.5 oz ai/acre, and a methylated seed oil (MSO) at.5 percent v/v. Sugar beet injury and weed control were evaluated throughout the season. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion Kochia control with the standard rate and micro-rate programs without preemergence Nortron was 97 and 96 percent, respectively (Table ). All treatments including both preemergence Nortron and postemergence UpBeet provided 00 percent control of kochia 66 days after treatment (DAT) on July. Kochia control with standard rate treatments without UpBeet gave 9-98 percent control and did not improve with increasing Nortron rates. Applying Nortron preemergence at 6, 4, or oz ai/acre followed by the standard rate program minus UpBeet gave similar kochia control compared with the standard treatment with UpBeet. The micro-rate program minus UpBeet gave 85, 89, and 9 percent kochia control with preemergence Nortron at 6, 4, and oz ai/acre, respectively. When Nortron was applied prior to the micro-rate treatment minus UpBeet only, the oz ai/acre rate provided similar kochia control compared to the micro-rate with UpBeet. Results from previous trials at the Malheur Experiment Station showed that Nortron applied preemergence at 48 oz ai/acre as part of a standard or micro-rate program minus UpBeet provided kochia control similar to both standard and micro-rate programs with UpBeet. The kochia population in this year's trial was less than in previous years and control obtained with Nortron at the evaluated rates may not hold up under greater kochia pressure. These data suggest that in field situations where ALS-resistant kochia is present, preemergence Nortron can improve control. Higher Nortron rates are required when using a micro-rate versus a standard rate program. All herbicide treatments gave 00 percent control of common lambsquarters and hairy nightshade. Pigweed control (i.e., Powell amaranth and redroot pigweed) was good to excellent (9-00 percent) with all treatments. The removal of UpBeet from the micro-rate program resulted in a significant decrease in barnyardgrass control compared to the micro-rate treatments with or without preemergence Nortron. The standard rate program with UpBeet following Nortron at 6 oz ai/acre provided 45 percent greater barnyardgrass control than the same treatment without UpBeet. Increasing the preemergence Nortron rate from 6 to 4 oz ai/acre and from 6 to oz ai/acre in the standard rate program without UpBeet resulted in and 40 percent greater barnyardgrass control, respectively. Sugar beet injury on May 5, 4 days after the third micro-rate application and 5 days after the second standard rate application, ranged from 5 to percent with the micro-rate treatments and from 5 to 9 percent with the standard rate treatments (Table ). By June, 7 days after the last application, sugar beet injury was similar among all treatments. Sugar beet injury was not related to increasing Nortron rates. Sugar beet root yields ranged from 44.8 to 49.7 tons/acre in herbicide-treated plots (Table ). Nortron applied at 6 oz ai/acre followed by the micro-rate without UpBeet produced 44.8 tons/acre root yield, which was significantly less than Nortron at oz ai/acre followed by the standard with UpBeet and Nortron at 4 oz ai/acre followed by the micro-rate Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

109 with UpBeet, both of which produced root yields of 49.7 tons/acre. These treatments represent the only significant differences in root yield among all herbicide treatments. The herbicide treatment with the lowest root yield, as mentioned above, also provided the lowest kochia control of any treatment at 85 percent. In this trial, each additional 5 percent increase in kochia control resulted in a sugar beet root yield increase of.56 tons/acre. When we combined data from the last years of kochia control trials at the Malheur Experiment Station, there is an increase in root yield of.7 tons/acre with each additional 5 percent kochia control (Fig. ). There were no differences among treatments with regard to percent sucrose content or percent extraction (Table ). Estimated recoverable sucrose (ERS) yields ranged from,54 to,648 lbs/acre in herbicide-treated plots (Table ). Nortron at 4 oz ai/acre preceding the standard program with UpBeet resulted in a significantly higher ERS yield than the total postemergence standard rate treatment with UpBeet. Nortron applied at 6 oz ai/acre followed by the micro-rate with UpBeet resulted in,9 and,97 lbs/acre greater ERS than Nortron applied at either 6 or 4 oz ai/acre followed by the micro-rate without UpBeet. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

110 Table. Kochia control in sugar beets with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed Lambs- Hairy Barnyard- Kochia spp. quarters Nightshade grass Treatment* Rate Timing oz ai/acre % Untreated control Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Micro-Rate Program % v/v, 4 Progress + UpBeet + Stinger + MSO % v/v 6, 7 Progress + UpBeet + Stinger + MSO Nortron fb 6.0 Standard with UpBeet --,5, Nortron fb 4.0 Standard with UpBeet --,5, Nortron fb.0 Standard with UpBeet --,5, Nortron fb 6.0 Standard w/out UpBeet --,5, Nortron fb 4.0 Standard w/out UpBeet --,5, Nortron fb.0 Standard w/out UpBeet --,5, Nortron fb 6.0 Micro with UpBeet --,4,6, Nortron fb 4.0 Micro with UpBeet --,4,6, Nortron fb.0 Micro with UpBeet --,4,6, Nortron fb 6.0 Micro w/out UpBeet --,4,6, Nortron fb 4.0 Micro w/out UpBeet --,4,6, Nortron fb.0 Micro w/out UpBeet --,4,6, LSD ( 0.05) 7 8 NS NS NS 5 *fb = Followed by. Application timings were () April preemergence, () April 9 to cotyledon beets, () April to full cotyledon beets, (4) April 6 to cotyledon to beets, (5) April 0 to beets, (6) May to - to beets, and (7) May 6 to 0-leaf beets. The untreated control was not included in the weed control analysis. Pigweed species included Powell amaranth and redroot pigweed.table. Sugar beet injury and yield with preemergence Nortron in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

111 Sugar beet Injury Yield Treatment* Rate Timing Root yield Sucrose Extraction ERS oz ai/acre % ton/acre % lb/acre Untreated control ,80 Standard Rate Program Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger ,5 Micro-Rate Program % v/v, 4 Progress + UpBeet + Stinger + MSO % v/v 6, 7 Progress + UpBeet + Stinger + MSO ,5 Nortron fb 6.0 Standard with UpBeet --,5, ,970 Nortron fb 4.0 Standard with UpBeet --,5, ,648 Nortron fb.0 Standard with UpBeet --,5, ,06 Nortron fb 6.0 Standard w/out UpBeet --,5, ,89 Nortron fb 4.0 Standard w/out UpBeet --,5, ,85 Nortron fb.0 Standard w/out UpBeet --,5, ,495 Nortron fb 6.0 Micro with UpBeet --,4,6, ,5 Nortron fb 4.0 Micro with UpBeet --,4,6, ,7 Nortron fb.0 Micro with UpBeet --,4,6, ,89 Nortron fb 6.0 Micro w/out UpBeet --,4,6, ,58 Nortron fb 4.0 Micro w/out UpBeet --,4,6, ,54 Nortron fb.0 Micro w/out UpBeet --,4,6, ,99 LSD (0.05) 6 NS. NS NS,8 *fb = Followed by. Application timings were () April preemergence, () April 9 to cotyledon beets, () April to full cotyledon beets, (4) April 6 to cotyledon to beets, (5) April 0 to beets, (6) May to - to beets, and (7) May 6 to 0-leaf beets. The untreated control was not included in the sugar beet injury analysis. ERS = Estimated recoverable sucrose. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

112 Figure. Response of sugar beet root yields to percent kochia control combined over a -year period from 00 to 00, Malheur Experiment Station, Oregon State University, Ontario, OR. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 96-0

113 TIMING OF OUTLOOK AND DUAL MAGNUM APPLICATIONS FOR WEED CONTROL IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Outlook (dimethenamid-p) and Dual Magnum (s-metolachlor) are soil-active herbicides that are labeled for postemergence application in sugar beet. Outlook can be applied to two-leaf or larger beets and Dual Magnum may be applied to one-leaf or larger beets. Outlook or Dual Magnum were applied as part of a standard rate program in the second or third postemergence application or as a lay-by application. The objectives of this trial were ) to determine if weed control can be improved with Outlook or Dual Magnum in the standard rate program, and ) to determine if the application timing of these herbicides influences weed control or crop response. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 4, 00. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April, kochia, pigweed, and common lambsquarters seed was spread over the entire experimental area to promote an even weed distribution. After planting, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May and 4. Plots were sidedressed on June with 76 lb nitrogen (urea), 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre boron. All plots were treated with Roundup (0.75 lb ai/acre) prior to sugar beet emergence on April. On May 6, Temik 5G (4 lb/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 7 and again on July with Super Six liquid sulfur (6 pt/acre), Topsin M (0.5 lb/acre) was applied on August 4. All fungicide treatments were applied by air. Herbicide treatments were broadcast-applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. Soil-active herbicides were applied at various timings as part of a standard rate herbicide program to evaluate the effect of application timing on weed control and crop response with the selected herbicides. The standard rate program consisted of Progress (ethofumesate + desmedipham + phenmedipham) applied at 4.0, 5.4, and 6.7 oz ai/acre in applications one, two, and three, respectively. UpBeet (triflusulfuron) was applied at oz ai/acre in all three applications and Stinger (clopyralid) at.5 oz ai/acre in the last two applications. Soil-active herbicides included Outlook, Dual Magnum, and Treflan (trifluralin). Outlook was applied at.0 oz ai/acre when applied in the second or third application or as a lay-by following the last cultivation. When split across the first and second applications, Outlook was applied at 0.5 and 5. oz ai/acre, respectively. Treflan at 6 oz ai/acre was applied with Outlook as a lay-by. Dual Magnum was applied at 0.8 oz ai/acre in the second or third application or as a lay-by. The first, second, third, and lay-by applications were made on April, April 0, May 6, and May, to cotyledon,, 0-leaf, and beets, respectively. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 06-09

114 Sugar beet injury and weed control were evaluated throughout the season. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion Outlook or Dual Magnum, when added to the standard rate program whether applied in the second or third application or as a lay-by application, did not improve broadleaf weed control compared to the standard rate treatment without any soil-active herbicides (Table ). All treatments resulted in 97 percent or greater control of broadleaf weed species. Treatments including Outlook or Dual Magnum, regardless of when they were applied, controlled barnyardgrass significantly better than the standard rate treatment without a soil-active herbicide application. Barnyardgrass control was greater with Outlook compared to Dual Magnum when applied in the third standard rate application. Control of barnyardgrass with Outlook was similar whether applied in the second, third, or lay-by applications. Control of barnyardgrass with Dual Magnum was greater when applied in the second application than when applied in the third or lay-by applications. Sugar beet injury on May 5 was greater with treatments where Outlook or Dual Magnum were applied in the second application compared to the standard treatment alone (Table ). Injury on May 5, which was only 4 days after the third standard rate application, was similar between treatments with Outlook or Dual Magnum in the third application and the standard treatment without Outlook or Dual Magnum. There were no differences in sugar beet injury among treatments on June (7 days after treatment). Sugar beet root yields associated with herbicide treatments ranged from 47.7 to 49.5 tons/acre and were significantly greater than the untreated control (Table ). Estimated recoverable sucrose yields were similar among herbicide treatments and were greater than the untreated control. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 06-09

115 Table. Weed control in sugar beet with standard rate herbicide treatments including postemergence applications of Outlook and Dual Magnum, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Kochia Pigweed spp. Lambsquarters Hairy nightshade Barnyardgrass Treatment Rate Timing* oz ai/acre % Untreated control Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Outlook Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger + Outlook Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Outlook Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Outlook + Treflan Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Dual Magnum LSD (0.05) NS NS NS NS 5 *Application timings were () April to cotyledon beets, () April 0 to beets, () May 6 to 0-leaf beets, (4) May lay-by to beets. The untreated control was not included in the weed control analysis. Pigweed species included Powell amaranth and redroot pigweed. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 06-09

116 Table. Sugar beet injury and yield with standard rate herbicide treatments including postemergence applications of Outlook and Dual Magnum, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Injury Yield Treatment Rate Timing* yield Sucrose Extraction ERS Untreated control ,095 Progress + UpBeet ,896 Progress + UpBeet + Stinger Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Outlook Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger + Outlook Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Outlook Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Outlook + Treflan Progress + UpBeet Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet + Stinger Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger + Dual Magnum Progress + UpBeet Progress + UpBeet + Stinger Progress + UpBeet + Stinger Dual Magnum Root , , , , , , , ,94 LSD (0.05) 5 NS 4. NS NS,49 *Application timings were () April to cotyledon beets, () April 0 to beets, () May 6 to 0-leaf beets, (4) May lay-by to beets. The untreated control was not included in the sugar beet injury analysis. Sugar beets were harvested on October 6-7, 00. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 06-09

117 VARIABLE UPBEET AND PROGRESS RATES IN STANDARD AND MICRO- RATE HERBICIDE PROGRAMS IN SUGAR BEET Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Obtaining satisfactory weed control using the micro-rate program in western sugar beet regions can be difficult when conditions of low humidity and/or a lack of spring precipitation events exist prior to or during herbicide applications. Spring precipitation can increase the efficacy of preemergence applications as well as produce weed flushes that can be controlled by postemergence applications. Weed seedlings growing under dry conditions can be stressed, making them harder to control. In addition, weeds growing under dry conditions often have a heavy wax cuticle on the leaf surface that reduces herbicide penetration. Difficulties in obtaining satisfactory weed control with the micro-rate herbicide program has sparked interest in evaluating weed control and crop response with increased Progress and/or UpBeet rates within the micro-rate program. Methods This trial was established at the Malheur Experiment Station under furrow irrigation on April 4, 00. Sugar beets (Hilleshog 'PM-') were planted in -inch rows at a -inch seed spacing. On April, kochia, pigweed, and common lambsquarters seed was spread over the entire experimental area to promote an even weed distribution. After planting, the trial was corrugated and Counter 0 CR was applied in a 7-inch band over the row at 6 oz/,000 ft of row. Sugar beets were thinned to 8-inch spacing on May and 4. Plots were sidedressed on June with 76 lb nitrogen (urea), 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre boron. All plots were treated with Roundup (0.75 lb ai/acre) prior to sugar beet emergence on April. On May6, Temik 5G (4 lb/acre) was applied for sugar beet root maggot control. For powdery mildew control, Headline ( fl oz/acre) was applied on June 7 and again on July with Super Six liquid sulfur (6 pt/acre). Topsin M (0.5 lb/acre) was applied on August 4. All fungicide treatments were applied by air. Herbicide treatments were broadcast-applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. Treatments in this trial were designed to evaluate both weed control and crop response with increasing Progress (ethofumesate + desmedipham + phenmedipham) and/or UpBeet (triflusulfuron) rates within the standard and micro-rate weed control programs. Progress rates ranged from 4.0 to 0.8 oz ai/acre in selected standard rate treatments and from.8 to.6 oz ai/acre with selected micro-rate treatments. UpBeet rates used in standard rate treatments ranged from to 0.5 oz ai/acre and from 0.08 to 0.66 oz ai/acre with micro-rate treatments. Stinger (clopyralid) was applied at 0.5 oz ai/acre in the micro-rate program and at.5 oz ai/acre in the standard rate program. Outlook (dimethenamid-p) at.0 oz ai/acre was applied postemergence in either the second or third application of selected micro-rate treatments and in the second application of selected standard rate treatments. Nortron (ethofumesate) was applied preemergence at a rate of 8.0 oz ai/acre and postemergence at rates of 0.5,.0, and.0 oz ai/acre in selected treatments. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

118 Sugar beet injury and weed control were evaluated throughout the season. Sugar beet yields were determined by harvesting the center two rows of each plot on October 6 and 7. Root yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for weed control or crop response. Results and Discussion There were no differences (P = 0.05) in weed control among the herbicide treatments on June 0 (46 days after treatment [DAT]) (Table ). On August 5 (8 DAT), kochia control was similar among herbicide treatments ranging from 95 to 00 percent. Pigweed control was less, even at 94 percent control, with the traditional microrate than all other treatments on August 5. Herbicide treatments gave 00 percent control of hairy nightshade and 97 to 00 percent control of common lambsquarters on August 5. Barnyardgrass control was 98 percent or higher evaluated on June 6 ( DAT). Weed control in this trial was excellent with all of the herbicide treatments, regardless of the Progress or UpBeet rates. Sugar beet injury was observed on May 5, 5 days after the second standard rate and 4 days after the third microrate postemergence applications (Table ). Injury ranged from to 40 percent and was greatest with the standard rate treatment applied in combination with methylated seed oil (MSO). The protocol called for 0.5 percent v/v MSO but was inadvertently applied with the traditional micro-rate amount of.5 percent v/v. On June (8 DAT), this treatment again displayed the greatest injury. On June, sugar beet injury with micro-rate treatments was greater when Outlook and/or Nortron were included in postemergence applications compared to micro-rate treatments alone. Increasing the rates of Progress and/or UpBeet in micro-rate treatments without postemergence Outlook or Nortron did not injure sugar beet more than the traditional micro-rate treatment. Increasing the rate of UpBeet from to 0.74 oz ai/acre in the first applications and from to 0.5 oz ai/acre in the third application significantly increased sugar beet injury on both May 5 and June with the standard rate treatment with Outlook. By June 6 ( DAT), differences in sugar beet injury were not detectable among treatments. In spite of treatment differences with regard to crop injury, yields were not affected by herbicide treatments. Sugar beet root yields were similar among herbicide treatments, ranging from 4.8 to 47. tons/acre, all of which were significantly greater than the untreated control (Table ). There were no differences in either sucrose content or extraction among any of the treatments. All herbicide treatments had estimated recoverable sucrose yields greater than the untreated control. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

119 Table. Weed control with variable UpBeet and Progress rates in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed Lambs- Hairy Barnyardgrass Kochia spp. quarters nightshade Treatment Rate Timing* oz ai/acre % v/v % Untreated control Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO ,6, Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + Outlook + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + MSO Progress + UpBeet + Stinger + Nortron + MSO Progress + UpBeet + Stinger + Nortron + Outlook + MSO Progress + UpBeet + Stinger + Nortron + MSO Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + Outlook + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet + MSO Progress + UpBeet+ Stinger + Outlook + MSO Progress + UpBeet+ Stinger + MSO , Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

120 Table. (continued) Weed control with variable UpBeet and Progress rates in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Kochia Pigweed spp. Lambsquarters Hairy nightshade Barnyardgrass Treatment Rate Timing* % oz ai/acre % v/v Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO ,7 4,6, LSD (0.05) NS NS NS *Application timings were () April preemergence, () April 9 to cotyledon sugar beets, () April to full cotyledon sugar beets, (4) April 6 to cotyledon to sugar beets, (5) April 0 to sugar beets, (6) May to - to sugar beets, and (7) May 6 to 0-leaf sugar beets. Pigweed species included Powell amaranth and redroot pigweed. The untreated control was not included in the weed control analysis. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

121 Table. Sugar beet injury and yield with variable UpBeet and Progress rates in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Injury Yield Treatment Rate Timing* yield Sucrose Extraction ERS oz ai/acre % v/v % ton/acre % lb/acre Untreated control ,08 Nortron ,977 Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO ,6,7 Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + Outlook + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + MSO Progress + UpBeet + Stinger + Nortron + MSO Progress + UpBeet + Stinger + Nortron + Outlook + MSO Progress + UpBeet + Stinger + Nortron + MSO Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + Outlook + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet + MSO Progress + UpBeet+ Stinger + Outlook + MSO Progress + UpBeet+ Stinger + MSO , Root , , , , , ,985 Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

122 Table. (continued) Sugar beet injury and yield with variable UpBeet and Progress rates in standard and micro-rate herbicide programs, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Injury Yield Treatment Rate Timing* Root yield Sucrose Extraction ERS Oz ai/acre % v/v % ton/acre % lb/acre , Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet Progress + UpBeet + Stinger + Outlook Progress + UpBeet + Stinger Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO Progress + UpBeet + Stinger + MSO Nortron Progress + UpBeet + MSO Progress + UpBeet + Stinger + MSO ,7 4,6, , , ,000 LSD (0.05) 6 6 NS 4.4 NS NS,4 *Application timings were () April preemergence, () April 9 to cotyledon sugar beets, () April to full cotyledon sugar beets, (4) April 6 to cotyledon to sugar beets, (5) April 0 to sugar beets, (6) May to - to sugar beets, and (7) May 6 to 0-leaf sugar beets. The untreated control was not included in the sugar beet injury analysis. Sugar beets were harvested on October 6 and 7, 00. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-0

123 ROTATIONAL RESPONSE OF ALFALFA AND SUGAR BEET TO CLARION AND STEADFAST HERBICIDES Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Informed herbicide selection in diverse crop rotations is crucial to avoid adverse effects on future crops from herbicide carryover. Sulfonylurea herbicides are some of the most effective and low-use rate herbicides available. However, the rotational restrictions can be as long as 6 months for selected crops. One such herbicide is Steadfast 75 WDG which is a premix of the sulfonylurea herbicides nicosulfuron and rimsulfuron at a : ratio. Steadfast provides selective postemergence (POST) grass and broadleaf weed control in field corn. Steadfast has a rotational restriction of months for alfalfa and 0-8 months, depending on soil ph, for sugar beet. A newly registered product, Clarion 75 WDG (formerly DPX-79406) also consists of nicosulfuron and rimsulfuron but in a : ratio. The reduced amount of nicosulfuron in Clarion compared to Steadfast may potentially decrease the rotational restrictions for sugar beet and alfalfa. A field trial was conducted to evaluate the rotational tolerance of alfalfa and sugar beet to Clarion and Steadfast herbicides. Materials and Methods Clarion and Steadfast were applied postemergence (POST) to field corn on May 9, 00 preceding alfalfa and sugar beet establishment in the spring of 00. Clarion was applied at the labeled rate of 0.75 oz ai/acre and at twice the labeled rate at 0.75 oz ai/acre. Steadfast also was applied at x and x rates of 0.56 and. oz ai/acre, respectively. Steadfast and Clarion were applied to corn plots measuring 0 by 0 ft. Treatments were arranged in a randomized complete block design with four replicates. Plot size for the rotational crops measured 0 by 0 ft with half of the original 0 by 0 ft plots planted to alfalfa and the other half to sugar beet in 00. Following corn harvest the trial area was roto-tilled on October 8 and bedded on -inch rows on November 7, 00. Alfalfa (var. Surpass) was seeded at a rate of 0 lb/acre on April 0, 00 ( months after treatment [MAT]). Sugar beets (var. Hilleshog PM ) were planted on April 0, 00 ( MAT) at a -inch seed spacing (~4,000 seeds/acre). After sugar beet planting, the trial was corrugated and Counter 0 CR was applied in a 7- inch band over the row at a rate of 6 oz/,000 ft of row. Temik 5G was applied on June for sugar beet root maggot control at a rate of 9.5 oz/,000 ft of row. Plots were sidedressed with 76 lb nitrogen, 96 lb phosphate, 00 lb potash, 8 lb sulfates, 6 lb elemental sulfur, lb zinc, and lb/acre of boron on June, 00. Sugar beets were thinned to an 8-inch plant spacing (~5,640 plants/acre) on June 0, 00. The soil was an Owyhee silt loam with a sand, silt, and clay content of 9, 6, and 8 percent, respectively. A soil test determined a ph of 8.0, cation exchange capacity of, and an organic matter content of.8 percent. Weeds were controlled in both the alfalfa and sugar beet plots using hand labor. Sugar beet and alfalfa injury were evaluated throughout the season. The alfalfa stand was evaluated by counting seedlings within four, -ft² quadrats in each plot on May 9. The sugar beet stand was evaluated by counting the number of plants within the entire length of the center two rows in each plot prior to thinning on May 9 and again prior to harvest on October 7. Sugar beet yields were determined by harvesting the center two rows of Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-7

124 each plot on October 7. Sugar beet yields were adjusted to account for a 5 percent tare. One sample of 6 beets was taken from each plot for quality analysis. The samples were coded and sent to Hilleshog Mono-Hy Research Station in Nyssa, Oregon, to determine beet pulp sucrose content and purity. Sucrose content and recoverable sucrose were estimated using empirical equations. Alfalfa yields were determined by cutting a -ft by 6-ft swath from the center of each plot using a flail mower on July 5 and August. Biomass from the harvest area was weighed to determine the total fresh weight. A subsample was weighed from each plot and dried in a forced air dryer at 40 F. Once dry, the sample was removed and reweighed to determine the percent moisture at the time of cutting. Alfalfa forage yield was reported based on percent moisture. Data were analyzed using analysis of variance procedures and means were separated using protected LSD at the 95 percent confidence interval (P = 0.05). The untreated control was not included in the analysis of variance for crop injury. Results and Discussion Injury to seedling alfalfa planted months after POST-applied Steadfast and Clarion ranged from 0 to 66 percent on May 9, 00 (65 days after treatment [DAT]) (Table ). Injury to alfalfa seedlings consisted of stunting and chlorosis of new growth. The greatest alfalfa injury was observed with Steadfast at. oz ai/acre. Clarion applied at 0.75 oz ai/acre produced significantly less injury than all other herbicide treatments 65 DAT. Herbicide carryover also resulted in reduced alfalfa stand. At 65 DAT, all herbicide treatments except Clarion applied at 0.75 oz ai/acre resulted in a significant alfalfa stand loss compared to the untreated control. Alfalfa injury on July (97 DAT) was similar with both Clarion treatments and Steadfast at 0.56 oz ai/acre. Injury with Steadfast at. oz ai/acre was greater than all other herbicide treatments at 8 percent. Injury associated with Clarion treatment did not significantly reduce forage yield on July 5. Herbicide injury resulted in reduced forage yield on July 5 for both Steadfast treatments. There was no visually detectable injury to alfalfa regrowth on July 4, 0 days after the first cutting (data not shown). Yields from the second cutting on August 0 were similar among all treatments. Sugar beet injury on May 9, (65 DAT), ranged from 5 to 59 percent (Table ). Injury was greater with Steadfast at. oz ai/acre than from all other treatments. Sugar beet injury was similar with the labeled rate of Steadfast (0.56 oz ai/acre) and with Clarion applied at twice its labeled rate at 0.75 oz ai/acre. Clarion applied at the labeled rate of 0.75 oz ai/acre injured sugar beet significantly less than all other herbicide treatments on May 9, 00. Sugar beet injury on July (97 DAT) was greatest with Steadfast applied at. oz ai/acre. All other herbicide treatments provided similar injury. Sugar beet stand on May 9 (65 DAT) was not different among treatments prior to thinning. Steadfast applied at. oz ai/acre was the only treatment that reduced stand compared to the untreated control prior to harvest on October 7. There were no significant differences among treatments with regard to root yield, percent sucrose content, or estimated recoverable sucrose yields. Since this trial was conducted, Clarion has been registered for use in field corn. The label stipulates the same rotational restriction of months for alfalfa as does the Steadfast label. The rotational restriction for sugar beet following Steadfast application is 0 months for soils with ph < 6.5 and 8 months with ph > 6.5. The rotational restriction for sugar beet following Clarion application is 0 months, regardless of soil ph. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-7

125 Table. Alfalfa injury, stand, and yield in response to Clarion and Steadfast herbicides applied the previous year to field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Alfalfa Alfalfa Alfalfa Alfalfa Alfalfa Injury Injury Stand Yield Yield Treatment* Rate 5/9 7/ 5/9 7/5 8/ oz ai/acre % % No/ft ton/acre ton/acre Clarion Clarion Steadfast Steadfast Untreated control LSD(0.05) NS *Treatments were applied to field corn on May 9, 00. Clarion and Steadast were applied at x (0.75 or 0.56 oz ai/acre) and x (0.75 or. oz ai/acre) the labeled rates, respectively. Alfalfa was seeded on April 0, 00. The untreated control was not included in the analysis of variance for alfalfa injury. Alfalfa forage yields were adjusted to a moisture content of percent. Table. Sugar beet injury, stand, and yield in response to Clarion and Steadfast herbicides applied the previous year to field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Sugar beet Sugar beet Sugar beet Sugar beet Sugar beet Sugar beet Sugar beet Injury Injury Stand Stand Yield Yield Yield Treatment* Rate 5/9 7/ 5/9 0/7 Root Sucrose ERS oz ai/acre % % No./0' No./0' ton/acre % lb/acre Clarion ,90 Clarion ,98 Steadfast ,807 Steadfast ,759 Untreated control ,909 LSD (0.05) 6 NS.0 NS NS NS *Treatments were applied to field corn on May 9, 00. Clarion and Steadast were applied at x (0.75 or 0.56 oz ai/acre) and x (0.75 or. oz ai/acre) the labeled rates, respectively. Sugar beets were planted April 0 and harvested on October 7, 00. The untreated control was not included in the analysis of variance for sugar beet injury. Sugar beet stands on May 9 were recorded prior to hand thinning on June 0, 00. ERS = Estimated recoverable sucrose Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 055. Pg 4-7

126 Weed Control and Crop Response with Herbicides Applied in Field Corn Charles A. Rice, Corey V. Ransom, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Weed control is important in corn production to reduce competition to the crop and reduce the production of weed seed for future crops. Field trials were conducted to evaluate preemergence and postemergence herbicides for weed control and crop tolerance in furrow-irrigated field corn. Herbicides evaluated include Steadfast, DPX-79406, Callisto, and Option. Steadfast is a premix of the sulfonylurea herbicides (i.e., ALS inhibiting) nicosulfuron and rimsulfuron at a : ratio. Steadfast provides selective postemergence grass and broadleaf weed control in field corn. The experimental product DPX also consists of nicosulfuron and rimsulfuron but in a : ratio, and will potentially be marketed for corn grown in rotation with sugar beet. Callisto (mesotrione) is a new herbicide that has a unique mode of action compared to those of previously registered broadleaf herbicides. Callisto inhibits amino acid conversion and carotenoid biosynthesis, leaving chlorophyll in affected plants unprotected from decomposition by sunlight. Because of this unique mode of action, mesotrione provides effective control of triazine- sulfonylurea- and other ALS-resistant weeds. Callisto can be applied pre- or postemergence to control annual broadleaf weeds in field corn, production seed corn, and corn grown for silage. Option (foramsulfuron) is a new postemergence sulfonylurea herbicide that controls annual and perennial grass and broadleaf weeds in field corn. Option contains a safener that is intended to enhance the ability of corn to recover from any yellowing or stunting associated with the application of sulfonylurea herbicides. Materials and Methods General Roundup was applied preplant at 0.75 lb ai/acre to control volunteer wheat on May 6. Golden Harvest variety 'H-98' (0 day relative maturity) field corn was planted with a John Deere model 7 Flexi Planter on May 7, 00. Seed spacing was one seed every 7 inches on 0-inch rows. Plots were 0 by 0 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Plots were sidedressed with 80 lb N, 0 lb P, 4 lb Zn and Mn, lb B, and lb elemental S/acre on April 4. Herbicide treatments were applied with a CO -pressurized backpack sprayer calibrated to deliver 0 gal/acre at 0 psi. Crop response and weed control were evaluated throughout the growing season. Corn yield was determined by harvesting ears from 5-ft sections of the center two rows in each four-row plot on October 7-9. The harvested ears were shelled and grain dry weight and percent moisture content were recorded. Grain yields were adjusted for a percent moisture content. Data were analyzed using ANOVA, and treatment means were separated using Fishers protected LSD (P = 0.05). Preemergence Grass Herbicide Efficacy and Crop Safety Treatments included Steadfast (0.05 lb ai/acre) applied postemergence with either Callisto (0.047 lb ai/acre) plus Aatrex (0.75 lb ai/acre) or Distinct (0.087 lb ai/acre). Steadfast combinations were applied either as a total postemergence program or following preemergence applications of Bicep II (.0 lb ai/acre) or Dual II Magnum (.6 lb ai/acre). Total postemergence Steadfast combinations were applied early postemergence on May 8. Steadfast combinations following preemergence Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

127 applications were applied late postemergence on June. Steadfast combinations were compared to standard treatments including either Bicep II (.5 lb ai/acre), Harness Xtra (.0 lb ai/acre), or Harness (.75 lb ai/acre), applied preemergence followed by Clarity (. lb ai/acre) plus NIS ( percent v/v) or preemergence Dual II Magnum (.6 lb ai/acre) followed by Marksman (. lb ai/acre) plus NIS. All postemergence treatments including Steadfast were applied with COC (.0 percent v/v) plus AMS (.0 lb product/acre). Weed Control with DPX and Steadfast Combinations Weed control was compared between DPX and Steadfast, which contain the same active ingredients (nicosulfuron plus rimsulfuron) at different ratios. DPX was applied preemergence and postemergence at 0.75 oz ai/acre. DPX was also applied preemergence with Callisto at 4.0 oz ai/acre. Weed control with preemergence treatments of DPX and DPX plus Callisto were compared to Dual II Magnum. DPX was applied postemergence alone and in various combinations with Aatrex (8.0 or 4.0 oz ai/acre), Callisto (0.75 or.0 oz ai/acre), or Distinct (.4 oz ai/acre). Steadfast was applied postemergence at 0.56 oz ai/acre alone and in combinations with Callisto (.0 oz ai/acre) or Distinct (.4 oz ai/acre). Postemergence applications of DPX and Steadfast were applied with MSO (.0 percent v/v) except for combinations including Callisto, which were applied with COC (.0 percent v/v) or Distinct, which were applied with NIS ( percent v/v). All postemergence applications included percent N at.5 percent v/v. Grass control with DPX and Steadfast were compared with Option herbicide combined with Callisto. Weed Control with Option Combinations Option was applied postemergence at 0.0 lb ai/acre to corn at the V growth stage on May 8. Option was applied alone and in combinations with Distinct (0.044, 0.087, and 0.75 lb ai/acre), Callisto (0.047, 0.06, and lb ai/acre), Define (0.5, 0.5, and 0. lb ai/acre), Outlook (0.47 lb ai/acre), and Dual II Magnum (0.96 lb ai/acre). Treatments of Steadfast (0.05 lb ai/acre) plus Dual II Magnum and COC (.5 percent v/v) or Callisto (0.06 lb ai/acre) were included for comparison. All treatments included percent N at.5 percent v/v. Broad Spectrum Weed Control with Dual II Magnum and Callisto Callisto was applied preemergence at 0.87 lb ai/acre with Dual II Magnum (.59 lb ai/acre) or Outlook (0.656 lb ai/acre). Callisto was applied postemergence at lb ai/acre alone, combined with Aatrex ( lb ai/acre), or following preemergence applications of Dual II Magnum, Outlook, or Option (0.0 lb ai/acre). Callisto treatment combinations were compared to the standard treatment of Dual II Magnum applied preemergence followed by a postemergence application of Distinct (0.75 lb ai/acre) plus NIS ( percent v/v) and 8 percent N (.5 percent v/v). All postemergence applications with Callisto included COC (.0 percent v/v) and 8 percent N ( percent v/v). Results and Discussion Preemergence Grass Herbicide Efficacy and Crop Safety Crop injury ranged from to 0 percent on June (4 and 8 days after early and late postemergence applications, respectively) (Table ). The only herbicide treatments that resulted in less than 00 percent control of Powell amaranth and redroot pigweed on July 0 were treatments of Steadfast plus Distinct plus COC and AMS applied early postemergence following Dual II Magnum or Bicep II (Table ). Barnyardgrass and green foxtail control on June (8 and 4 days after late and early postemergence applications, respectively) was excellent (9 to 97 percent) with all Steadfast combinations. However, by July 0 (58 and 6 days after late and early postemergence applications, respectively), annual grass control was greatest in plots receiving preemergence applications of Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

128 Bicep II or Dual II Magnum followed by late postemergence applications of Steadfast plus Callisto and Aatrex. The total late postemergence treatment of Steadfast plus Callisto and Aatrex provided similar annual grass control to the preemergence followed by late postemergence treatments but was not different from total early postemergence treatments on July 0. Common lambsquarters control was 00 percent with all treatments except for Dual II Magnum applied preemergence followed by Steadfast plus Distinct postemergence. Corn yields in herbicide-treated plots were similar among treatments and were all greater than the untreated control (Table ). Weed Control with DPX and Steadfast Combinations Crop injury from herbicide treatment on June ( days after postemergence applications) ranged from to 8 percent (Table ). Steadfast applied alone injured corn more than when applied in combinations with Callisto and Distinct. Preemergence treatments of DPX plus Callisto controlled Powell amaranth, redroot pigweed, and common lambsquarters better than Dual II Magnum on both June and July 0, 4 and 8 days after preemergence applications, respectively. (Table ). The addition of Callisto to DPX applied preemergence increased control of barnyardgrass and green foxtail over preemergence DPX alone. Preemergence treatments gave significantly less (P < 0.05) annual grass control compared to all postemergence treatments except Option plus Callisto, which gave annual grass control similar to DPX plus Callisto and Dual II Magnum on July 0 (6 days after postemergence applications). Powell amaranth, redroot pigweed, common lambsquarters, and hairy nightshade control were significantly (P < 0.05) greater with all postemergence combinations compared to preemergence treatments on both June and July 0. The addition of Aatrex (8.0 oz ai/acre) to postemergence DPX and DPX plus Callisto (0.75 oz ai/acre) increased Powell amaranth and redroot pigweed control by 8 and percent, respectively on July 0. Postemergence Steadfast gave percent greater control of Powell amaranth and redroot pigweed than DPX on July 0. The addition of Callisto or Distinct to Steadfast did not significantly increase control of any of the evaluated weed species. Annual grass control was similar among all DPX and Steadfast postemergence treatments. Common lambsquarters control with the addition of Aatrex to DPX was 0 and 7 percent greater compared to DPX alone on June and July 0, respectively. The combination of DPX plus Aatrex gave greater common lambsquarters control than combinations of DPX plus Callisto (0.75 oz ai/acre) or Distinct on July 0. DPX plus Aatrex controlled hairy nightshade 0 and 0 percent greater than DPX plus Distinct on June and July 0, respectively. Postemergence DPX and Steadfast treatments gave similar hairy nightshade control on July 0. Despite poor (79 percent on June and 54 percent on July 0) annual grass control, the postemergence treatment of Option plus Callisto resulted in the highest corn yield of 7 bu/acre (Table ). Option plus Callisto provided a higher corn yield than Steadfast plus Callisto and yield similar to DPX plus Callisto. Increasing the rate of Callisto from 0.75 to.0 oz ai/acre applied with DPX and/or DPX plus Aatrex did not result in an increase in weed control or corn yield. Weed Control with Option Combinations Corn injury from herbicide treatment ranged from to percent on June 4 (7 days after treatment [DAT]) and from 9 to percent on June (4 DAT) (Table ). Injury consisted of plant stunting due to shortened internodes and slight yellowing of foliage compared with the untreated control. Injury symptoms were undetectable on July 5 (8 DAT). All herbicide treatments gave 95 percent or greater Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

129 Powell amaranth and redroot pigweed control on June. Control of Powell amaranth and redroot pigweed on July 0 (6 DAT) was significantly (P < 0.05) improved over Option alone only when Callisto (0.06 lb ai/acre), Outlook (0.47 lb ai/acre), or Dual II Magnum (0.96 lb ai/acre) were applied with Option. Treatment combinations including Callisto provided greater common lambsquarters control on June than did treatments where Define was applied with Option. Hairy nightshade control ranged from 96 to 00 percent and was not different among herbicide treatments. Volunteer potato control was greater with Option plus Dual Magnum than with Steadfast plus Dual Magnum. Treatments including Callisto gave 79 to 84 percent control of volunteer potato on June. Option plus Callisto at lb ai/acre controlled volunteer potato greater than all tank-mix combinations of Option plus Distinct, Option plus Define, Option plus Dual Magnum or Outlook, and Steadfast plus Dual Magnum. Increasing the rate of Define from 0.5 to 0. lb ai/acre in a tank-mix with Option resulted in a 0 percent increase in annual grass control. Steadfast plus Callisto gave better annual grass control than did Option plus Callisto (0.06 lb ai/acre). Corn yields in herbicide-treated plots ranged from 67 to 86 bu/acre and were greater than the untreated control. The combination of Option plus Distinct (0.75 lb ai/acre) provided greater yield than the treatment of Option plus Define (0.5 lb ai/acre), representing the only significant yield difference among herbicide treatments. Broad Spectrum Weed Control with Dual II Magnum and Callisto Control of pigweed (Powell amaranth and redroot pigweed), common lambsquarters, and hairy nightshade were significantly greater with preemergence/postemergence combinations and total postemergence treatments compared to preemergence treatments (Table 4). The preemergence combination of Dual II Magnum plus Callisto controlled hairy nightshade more than the preemergence combination of Outlook plus Callisto on August (86 DAT). Callisto applied postemergence controlled annual grasses (barnyardgrass and green foxtail) poorly and was significantly improved by the addition of Aatrex to the postemergence application or when applied following preemergence applications of Dual II Magnum, Outlook, or Option. Treatments where Callisto was applied postemergence gave 7 to 96 percent volunteer potato control on June (4 DAT). Volunteer potato control was best when postemergence applications of Callisto followed preemergence applications of Dual II Magnum, Outlook, and Option. The addition of Aatrex to Callisto in total postemergence treatments significantly (P < 0.) increased volunteer potato control compared to Callisto alone (separation not shown). Corn yields in herbicide-treated plots were similar among treatments ranging from 84 to 07 bu/acre and were all greater than the untreated control. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

130 Table. Weed control and yield with preemergence and postemergence herbicides in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Crop injury Pigweed spp. Annual grass spp. Common Lambsquarters Corn Treatment Rate Timing* yield lb ai/acre % v/v % bu/acre Untreated control Bicep II.5 Clarity + NIS + % Dual II Magnum.6 Marksman + NIS. + % Bicep II Steadfast + Callisto + Aatrex + COC + AMS % Dual II Magnum Steadfast + Callisto + Aatrex + COC + AMS Bicep II + Steadfast + Distinct + COC + AMS Dual II Magnum + Steadfast + Distinct + COC + AMS Steadfast + Callisto + Aatrex + COC + AMS Harness Xtra Clarity + NIS Harness Clarity + NIS % % % % % % LSD (0.05) *Application timings were () preemergence on 5-8-0, () early postemergence on 5-8-0, and () late postemergence on Pigweed species were predominantly Powell amaranth mixed with some redroot pigweed. Annual grasses were predominantly barnyardgrass mixed with some green foxtail. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

131 Table. Weed control and yield with DPX and Steadfast combinations in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Crop injury Pigweed spp. Annual grass spp. Common lambsquarters Hairy nightshade Treatment Rate Timing* yield oz ai/acre % v/v % bu/acre Untreated control Dual II Magnum cd 5 DPX cd 6 DPX Callisto DPX MSO + % N DPX Aatrex + MSO + % N DPX Callisto + COC + % N DPX Callisto + Aatrex + COC + % N DPX Callisto + COC + % N DPX Callisto + Aatrex + COC + % N DPX Distinct + NIS + % N Steadfast + MSO + % N Steadfast + Callisto + COC + % N Steadfast + Distinct + NIS + % N Option + Callisto + COC + % N % % % % % % % % % % % c 8 POST ab 98 POST a 5 POST ab 99 POST a 97 POST ab 06 POST ab 07 POST b 07 POST ab 80 POST ab 90 POST ab 0 POST ab 7 LSD (0.05) *Herbicide treatments were applied preemergence () on and postemergence (POST) on Pigweed species were predominantly Powell amaranth mixed with some redroot pigweed. Annual grasses were predominantly barnyardgrass mixed with some green foxtail. The ANOVA was performed on arcsine square root percent transformed data. Mean separations were applied to nontransformed data. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

132 Table. Weed control, crop response, and yield with postemergence Option combinations in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Crop injury Pigweed spp. Common lambsquarters Hairy nightshade Vol. potato Annual grass spp. Treatment* Rate yield Untreated control Option + MSO + % N Option + Distinct + MSO + % N Option + Distinct + MSO + % N Option + Distinct + MSO + % N Option + Callisto + MSO + % N Option + Callisto + MSO + % N Option + Callisto + MSO + % N Option + Define + MSO + % N Option + Define + MSO + % N Option + Define + MSO + % N Option + Outlook + MSO + % N Option + Dual II Magnum + MSO + % N Steadfast + Dual II Magnum + COC + % N Steadfast + Callisto + MSO + % N Lb ai/acre % v/v % bu/acre f % % % % % % % % % % % % % % de b-e de de de cde de a-d ab ab a abc a-d 84 LSD (0.05) *Herbicide treatments were applied postemergence to corn at the V growth stage on Pigweed was predominantly Powell amaranth mixed with some redroot pigweed. Annual grasses were predominantly barnyardgrass mixed with some green foxtail. The ANOVA was performed on arcsine square root percent transformed data. Mean separations were applied to non-transformed data. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

133 Table 4. Weed control and yield with Dual II Magnum and Callisto in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Crop injury Pigweed spp. Common Lambsquarters Hairy nightshade Annual grass spp. Vol. potato Corn Treatment Rate Timing* yield lb ai/acre % v/v % bu/acre Untreated control e d Dual II Magnum.59 Callisto cd ab Callisto COC + 8% N.0 +.5% a c Dual II Magnum.59 Callisto Aatrex a a COC + 8% N.0 +.5% Outlook Callisto d bc Outlook Callisto + COC + 8% N Callisto + Aatrex + COC + AMS Outlook + Callisto + Aatrex + COC + 8% N Option + Callisto + COC + 8% N Dual II Magnum Distinct + NIS + 8% N % % % % +.5% a ab a ab a a ab ab bc ab LSD (0.05) *Herbicide treatments were applied () preemergence on and () postemergence to corn at the V growth stage on In columns where letter designations occur, the ANOVA was performed on arcsine square root percent transformed data. Mean separations were applied to non-transformed data. Pigweed was predominantly Powell amaranth mixed with some redroot pigweed. Annual grass species were predominantly barnyard grass mixed with some green foxtail. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. -9

134 Weed Control and Onion Tolerance with Soil-Active and Postemergence Herbicides Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 00 Introduction Weed control is essential for the production of marketable onions. Weed control in onion is difficult compared to many crops because of the lack of a complete crop canopy. Combinations of soil-active and postemergence herbicides are required to improve overall weed control. Weed control research is important in identifying potential herbicides and management strategies to improve weed control in onion production. Methods General Procedures Trials were conducted at the Malheur Experiment Station to evaluate experimental and registered herbicides for weed control and onion tolerance. The effect of spray volume on weed control and onion tolerance was also evaluated. Trials were conducted under furrow irrigation. Blanket applications were applied with a four-wheeler-mounted sprayer calibrated to deliver 0 gal/acre at 0 psi. All other herbicide treatments were applied with a CO -pressurized backpack sprayer calibrated to deliver 40 gal/acre at 0 psi. On March 9, onions (cv. 'Vaquero', Sunseeds, Morgan Hill, CA) were planted at a.7-inch spacing in double rows on -inch beds. Plots were four rows wide and 7 ft long and treatments were arranged in a randomized complete block design with four replicates. Lorsban was applied in a 6-inch band over each row at.7 oz/,000 ft of row. Onions were sidedressed with N at 75 lb/acre as urea on May and a second time on June 5. Registered insecticides and fungicides were applied for thrip and downy mildew control. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 6 and graded by size on September 5. Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Herbicide Application Timing for Pigweed Control in Onion Buctril and were applied at different rates and application timings alone and in combination to determine the most effective treatments for control of pigweed (Powell amaranth and redroot pigweed), common lambsquarters, and hairy nightshade. All treatments included a preemergence application of Roundup (0.75 lb ai/acre). Postemergence treatments were applied to one-, two-, three-, and five-leaf onions. At the five-leaf timing all treatments received an application of ( lb ai/acre). Herbicides and rates differed for applications to one-, two-, and three-leaf onions. Prowl and Outlook for Weed Control in Onion The soil-active herbicides Prowl, Prowl H O, and Outlook were evaluated for crop injury and weed control in onion. All plots received a preemergence application of Roundup at 0.75 lb ai/acre. Prowl and Prowl H O were compared at rates of 0.6 and.0 lb ai/acre applied to flag-leaf onions and to two-leaf onions at 0.6 lb ai/acre with Buctril ( lb ai/acre) plus Outlook (0.5 lb ai/acre). Postemergence applications of Outlook were applied either as a split application to two- and threeleaf onions or a single application at 0.66 or 0.84 lb ai/acre to two-leaf onions. Split applications of Outlook were applied twice at 0.5 lb ai/acre or at 0.66 and 0. lb ai/acre to two-leaf and three-leaf Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

135 onions, respectively. Outlook was applied with Buctril (0.5 or lb ai/acre), (0.5 or lb ai/acre), Prowl (0.5 or 0.6 lb ai/acre), or Prowl H O (0.6 lb ai/acre). All treatments consisting of four applications received an application of at lb ai/acre applied at the four-leaf stage. Soil-active Herbicides for Weed Control in Onion The soil-active herbicides Dacthal, Prowl, and Valor were evaluated for crop injury and weed control in onion. Various rates of Prowl and Dacthal were applied alone and in combination with Roundup. All herbicide-treated plots received a preemergence application of Roundup (0.75 lb ai/acre) applied with Prowl (0.6, 0.75, or 0.8 lb ai/acre) and/or Dacthal (5.0, 7.5, or 0.0 lb ai/acre) on April. The two-leaf applications consisted of Buctril (0.5 or lb ai/acre) plus Poast (0. lb ai/acre); Valor (0.06 or lb ai/acre) with and without crop oil concentrate (COC) (.0 percent v/v); or Buctril ( lb ai/acre) plus Valor (0.094 lb ai/acre) applied on May 7. Buctril ( lb ai/acre), ( lb ai/acre), and Poast (0. lb ai/acre) were applied to three-leaf onions on May 5 and ( lb ai/acre) plus Poast (0. lb ai/acre) were applied to four-leaf onions on May 0. Spray Volume Effects on Weed Control and Onion Injury Crop injury and weed control with spray volumes of 0, 0, and 60 gal/acre were evaluated for the herbicides Valor,, and Buctril. Herbicide rates evaluated were Valor applied at lb ai/acre plus a non-ionic surfactant (NIS) at percent v/v applied to two- and four-leaf onions; at 0. lb ai/acre applied to two- and four-leaf onions; and Buctril at 0.5 applied to two-leaf onions and lb ai/acre applied to four-leaf onions. Herbicides were applied to two-leaf onions on May 7 and to four-leaf onions on May 0. Results and Discussion Herbicide Application Timing for Pigweed Control in Onion In general, treatments with (0.56 lb ai/acre) applied to one-leaf onions or those where Buctril plus were applied to two- and three-leaf onions provided the best overall weed control (Table ). Pigweed control was increased when was applied with Buctril to one-leaf onions compared to Buctril alone. Treatments including Buctril at the two-leaf application timing provided significantly (P < 0.05) greater control of hairy nightshade than those without Buctril. The treatment including Outlook plus applied to two-leaf onions provided similar pigweed and hairy nightshade control compared to those treatments having Buctril plus applied at the same application timing. However, common lambsquarters control was greater from treatments where Buctril plus were applied to two-leaf onions compared with plus Outlook. Hairy nightshade control on June 9 (0 days after treatment [DAT]) was similar among treatments having Buctril or Outlook applied at the two-leaf application timing. Due to deteriorating weed control over time, late season weed control evaluations and onion yields were not taken for this trial. Prowl and Outlook for Weed Control in Onion Crop injury ranged from 4 to 7 percent on June (8 DAT) (Table ). Treatments including a fourleaf application of caused similar injury on June. Weed control with treatments including comparisons between Prowl and Prowl H O were not different (Table ). Common lambsquarters control was not different (P < 0.05) among herbicide treatments on either evaluation date. Prowl (.0 lb ai/acre) followed by applications of Buctril plus Outlook to two-leaf onions, plus Outlook to three-leaf onions, and applied to four-leaf onions were the only herbicide treatments that provided less than 60 percent hairy nightshade control on August 6. In general, the highest Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

136 marketable and total onion yields came from those treatments where was applied to two- and three-leaf onions or Outlook was applied at 0.66 lb ai/acre to two-leaf onions (Table ). Soil-active Herbicides for Weed Control in Onion Onion injury ranged from to 0 percent on May (6 days after the two-leaf application) and was greatest in plots receiving a two-leaf application of Buctril at lb ai/acre plus Valor at lb ai/acre (Table 5). However, by June ( DAT) crop injury associated with this treatment was similar to or less than all other herbicide treatments. Pigweed control was 00 percent on both June 9 (0 DAT) and August 6 (68 DAT) with the treatment including Dacthal (7.5 lb ai/acre) plus Prowl (0.6 lb ai/acre) preemergence followed by Buctril ( lb ai/acre) plus Valor (0.094 lb ai/acre) applied to two-leaf onions (Table 4). In general, greater common lambsquarters control was achieved when Buctril was applied to two-leaf onions compared to Valor alone with or without COC. However, the greatest common lambsquarters control was observed with Buctril at lb ai/acre plus Valor at lb ai/acre applied to two-leaf onions following a preemergence application of Roundup (0.75 lb ai/acre) plus Dacthal (7.5 lb ai/acre) and Prowl (0.6 lb ai/acre). Hairy nightshade control was greatest on August 6 when Valor at lb ai/acre was included in the herbicide program. Treatments with Valor at lb ai/acre provided 9 and 98 percent hairy nightshade control on August 6. All herbicide-treated plots provided marketable and total onion yields greater than the untreated control (Table 5). The herbicide program including the combination of Buctril ( lb ai/acre) plus Valor (0.094 lb ai/acre) applied to two-leaf onions provided greater colossal, super colossal, marketable, and total onion yields than all other treatments. The high onion yield associated with this treatment is directly related to season-long weed control that was 98 percent or greater for all species. Preemergence Nortron and Prowl for Weed Control in Onion On June (4 DAT) onion injury from herbicide treatments ranged from 4 to 6 percent and was significantly (P < 0.05) greater than the untreated control (Table 7). Pigweed control was greater with Prowl applied at.5 lb ai/acre than at 0.75 lb ai/acre on both June and August 6 (68 DAT) (Table 6). The addition of preemergence Nortron at both.0 and.0 lb ai/acre increased pigweed control over Prowl applied preemergence at 0.75 lb ai/acre and the Roundup-only preemergence treatment on August 6. Common lambsquarters control was greater on August 6 with preemergence applications of Prowl at.5 lb ai/acre, Nortron at.0 lb ai/acre, and all Prowl plus Nortron combinations compared to Roundup alone preemergence. The treatment including preemergence Nortron at.0 lb ai/acre and Prowl at 0.75 lb ai/acre was the only treatment that provided greater than 90 percent control of hairy nightshade on August 6. Spray Volume Effects on Weed Control and Onion Injury Increasing onion injury with Valor plus NIS from increasing spray volume was observed on all three evaluation dates (Table 8). This increase in injury may be attributed to the spray volume effects or to the increasing surfactant load as the NIS rate was applied at percent of the spray gallonage for all three spray volumes. Crop injury from applications was not affected by spray volume. Crop injury from Buctril decreased with increasing spray volume as observed on June (4 DAT). By June 9 (0 DAT), only Valor plus NIS applied at 0 and 60 gal/acre displayed injury greater than the untreated control. Common lambsquarters control 0 DAT with Valor plus NIS increased from 69 percent applied at 0 gal/acre to 9 percent applied at 60 gal/acre spray volume (Table 8). The opposite was true for Buctril; common lambsquarters control significantly decreased from 97 percent at 0 gal/acre down to 60 percent at 60 gal/acre spray volume. Due to deteriorating weed control over time, late-season weed control evaluations and onion yields were not taken for this trial. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

137 Table. Timing and rate of Buctril and for weed control in onions, Malheur Experiment Station, Oregon State University, Ontario, OR 00. Pigweed species Weed control Common lambsquarters Hairy nightshade Treatment* Rate Timing Lb ai/acre Crop stage % Untreated control Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril Buctril + Outlook Buctril leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf -leaf 5-leaf LSD (0.05) *All treatments received a preemergence application of Roundup (0.75 lb ai/acre). The application dates were: preemergence (April ), -leaf (May 9), (May 7), (May 5), and 5-leaf (May 0). Pigweed species at this location are predominantly Powell amaranth mixed with some redroot pigweed. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

138 Table. Weed control in onions with Prowl and Outlook, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed species Common lambsquarters Hairy nightshade Treatment* Rate Timing lb ai/acre Crop stage % Untreated control Prowl Buctril+Prowl+Outlook Buctril+Outlook flag Prowl H O Buctril+ProwlH O+Outlook Buctril+Outlook Prowl Buctril+Outlook Prowl H O Buctril+Outlook Prowl Buctril Prowl Buctril++Outlook Buctril++Outlook Prowl Buctril+Outlook +Outlook Prowl Buctril+Outlook Prowl Buctril++Outlook +Prowl+Outlook flag flag flag flag flag flag flag flag LSD (0.05) 5 5 NS 6 4 *All treatments received a preemergence application of Roundup (0.75 lb ai/acre). The application dates were: Preemergence (April ), flag (April ), (May 7), (May 5), and (May 0). Pigweed species at this location are predominantly Powell amaranth mixed with some redroot pigweed. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

139 Table. Onion injury and yield with Prowl and Outlook, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Onion yield Treatment Rate Timing* Onion injury Medium Jumbo Colossal Super colossal Total Marketable lb ai/acre Crop cwt/acre % stage Untreated control Prowl Buctril+Prowl+Outlook Buctril+Outlook flag Prowl H O Buctril+ProwlH O+Outlook Buctril+Outlook Prowl Buctril+Outlook Prowl H O Buctril+Outlook Prowl Buctril Prowl Buctril++Outlook Buctril++Outlook Prowl Buctril+Outlook +Outlook Prowl Buctril+Outlook Prowl Buctril++Outlook +Prowl+Outlook flag flag flag flag flag flag flag flag LSD (0.05) NS 8 NS *The application dates were: Preemergence (April ), flag (April ), (May 7), (May 5), and (May 0). Crop injury evaluations were taken on June, 8 days after the application. Plots were harvested on September 6 and onions were graded on September Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

140 Table 4. Weed control in onions with soil-active herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed species Common lambsquarters Hairy nightshade Treatment Rate Timing* lb ai/acre Crop stage % Untreated control d 0 d Roundup+Prowl Buctril+Poast Buctril++Poast +Poast Roundup+Dacthal Buctril+Poast Buctril++Poast +Poast Roundup+Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Roundup+Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Roundup+Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Roundup+Dacthal+Prowl Valor Buctril++Poast +Poast Roundup+Dacthal+Prowl Valor Buctril++Poast +Poast Roundup+Dacthal+Prowl Valor+COC Buctril++Poast +Poast Roundup+Dacthal+Prowl Buctril+Valor Buctril++Poast +Poast % v/v bc 67 c c 67 c bc 8 bc bc 77 bc b 86 b c 64 c bc 75 bc b 84 b a 00 a LSD (0.05) *The application dates were: () preemergence (April ), (May 7), (May 5), and (May 0). Pigweed species at this location are predominantly Powell amaranth mixed with some redroot pigweed. ANOVA was conducted on arcsine percent transformed data. Transformed mean separation applied to non-transformed data. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

141 Table 5. Onion injury and yield response to soil-active herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Onion injury Onion yield Treatment* Rate Timing 5-6- Medium Jumbo Colossal Super colossal Marketable Total lb ai/acre Crop stage ----% cwt/acre Untreated Prowl 0.75 Buctril+Poast Buctril++Poast Poast +0. Dacthal Buctril+Poast Buctril++Poast +Poast Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Dacthal+Prowl Buctril+Poast Buctril++Poast +Poast Dacthal+Prowl Valor Buctril++Poast +Poast Dacthal+Prowl Valor Buctril++Poast +Poast Dacthal+Prowl Valor+COC Buctril++Poast +Poast Dacthal+Prowl Buctril+Valor Buctril++Poast +Poast % v/v LSD (0.05) *All preemergence applications included Roundup at 0.75 lb ai/acre. The application dates were: () preemergence (April ), (May 7), (May 5), and (May 0). Plots were harvested on September 6 and onions were graded on September 4-5. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

142 Table 6. Preemergence Nortron and Prowl for weed control in onions, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed Common Hairy species lambsquarters nightshade Treatment Rate Timing* Crop lb ai/acre stage % Untreated control c 0 Prowl 0.75 Buctril++Poast d ab 67 Buctril++Poast Poast +0. Prowl Buctril++Poast Buctril++Poast +Poast Nortron Buctril++Poast Buctril++Poast +Poast Nortron Buctril++Poast Buctril++Poast +Poast Buctril++Poast Buctril++Poast +Poast Nortron+Prowl Buctril++Poast Buctril ++Poast +Poast Nortron+Prowl Buctril++Poast Buctril++Poast +Poast Nortron+Prowl Buctril++Poast Buctril++Poast +Poast Nortron+Prowl Buctril++Poast Buctril++Poast +Poast bc ab ab ab ab ab cd b ab b ab ab a a ab ab 7 LSD (0.05) *The application dates were: () preemergence (April ), (May 7), (May 5), and (May 0). In data columns with letter designations the ANOVA was conducted on arcsine percent transformed data. Transformed mean separation applied to non-transformed data. Pigweed species at this location are predominantly Powell amaranth mixed with some redroot pigweed. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

143 Table 7. Onion injury and yield with preemergence Nortron and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Onion yield Treatment Rate Timing* Onion injury Small Medium Jumbo Colossal Super colossal Marketable Total lb ai/acre Crop stage % cwt/acre Untreated control Prowl Poast Poast Poast +0. Prowl + Poast + Poast + Poast Nortron + Poast + Poast + Poast Nortron + Poast + Poast + Poast + Poast + Poast + Poast Nortron + Prowl + Poast + Poast + Poast Nortron + Prowl + Poast + Poast + Poast Nortron + Prowl + Poast + Poast + Poast Nortron + Prowl + Poast + Poast + Poast LSD (0.05) *The application dates were: () preemergence (April ), (May 7), (May 5), and (May 0). Onion injury was evaluated on June, 4 days after the application. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

144 Table 8. Effect of spray volume on onion injury and weed control with Buctril,, and Valor, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Treatment* Rate Spray volume Timing Onion injury Weed control Pigweed species Common Lambsquarters Hairy nightshade lb ai/acre gpa Crop stage % % Untreated Valor + NIS Valor + NIS Valor + NIS Valor + NIS Valor + NIS Valor + NIS Buctril Buctril Buctril Buctril Buctril Buctril % v/v % v/v % v/v % v/v % v/v % v/v LSD (0.05) *All treatments received a preemergence application of Roundup (0.75 lb ai/acre) on April. Treatments were applied on May 7 and May 0 to and onions, respectively. Weed control evaluations were taken on June 9 (0 DAT). Pigweed species at this location are predominantly Powell amaranth mixed with some redroot pigweed. The information in this report is for the purpose of informing cooperators in industry, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any pesticide. Pesticide labels should always be consulted before any pesticide use. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-8

145 Development of New Herbicide Options for Weed Control in Potato Production, 00 Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR Introduction Weed control in potatoes is essential for production of high-yielding marketable tubers. Herbicide options in potato production are often limited. Several herbicides currently registered for use in other crops show promise for use in potatoes. Spartan (sulfentrazone) and Valor (flumioxazin) are protoporphyrinogen oxidase (PPO) inhibitors that disrupt the enzyme system necessary for the production of chlorophyll. These herbicides represent a mode of action that is not currently used in potatoes and offer more effective hairy nightshade control than current herbicide programs. Outlook (dimethenamid-p) is similar to Dual (metolachlor) but controls a larger spectrum of weeds. Trials were conducted to evaluate new herbicides for weed control in potatoes. Materials and Methods General Four trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes. Potatoes were planted April and in an Owyhee silt loam soil with ph 7.5, 0.9 percent organic matter content, and a cation exchange capacity of 4. 'Russet Burbank' seed pieces were planted every 9 inches in 6-inch-wide rows. Potato seed pieces were treated with the fungicide/insecticide formulation Tops-MZ plus Gaucho at seed cutting. Experimental plots were four rows wide and 0 ft long. Plots were sidedressed with fertilizer (90 lb N, 4 lb Zn, 4 lb Mn, lb B, 44 lb elemental S/acre) and beds were reshaped with a Lilliston cultivator on April 8. Preemergence herbicides were applied and incorporated with sprinkler irrigation on May. Postemergence treatments were applied on May and 0. Treatments were broadcast applied with a CO -pressurized backpack sprayer delivering 0 gal/acre at 0 psi. Plots were sprinkler irrigated 4 times during the growing season according to crop requirements. Plots were treated with Ridomil Gold plus Bravo at lbs product/acre on June 4, Dithane on June 5 and July to prevent late blight, and with liquid sulfur on June 0 and August 4 to control powdery mildew. Potato injury and weed control were evaluated throughout the growing season. Tuber yields were taken by harvesting the center two rows of each plot. Weed biomass samples were taken from 5 ft of row within each plot on August 6. Plots were harvested on September 9-. Potatoes were graded for yield and size on September 7-4. Weed Control with Valor and Spartan Rates Weed control with preemergence applications of Valor at rates of 0.06, 0.078, 0.094, and 0.5 lb ai/acre and Spartan at rates of 0.5, 0.4, and 0.88 lb ai/acre were compared to Sencor (0.5 lb ai/acre) plus Dual Magnum (.0 lb ai/acre) and Matrix (0.008 lb ai/acre) plus Dual Magnum (.0 lb ai/acre). Treatments were replicated four times. Weed Control with Valor and Spartan Combinations Preemergence treatments of Valor and Spartan were applied alone and in combination with Outlook (0.656 lb ai/acre), Dual Magnum (.0 lb ai/acre), Prowl (.0 lb ai/acre), and Eptam (.0 lb ai/acre). Treatment rates for Valor and Spartan were and 0.4 lb ai/acre, respectively. Valor and Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85

146 Spartan treatments were compared to Outlook, Dual Magnum, Prowl, and Eptam alone, and to a tank mixture of Sencor plus Dual Magnum. Treatments were replicated four times. Weed Control with Outlook Combinations Outlook at lb ai/acre was applied preemergence with several herbicides including Prowl (.0 lb ai/acre), Prowl H O (.0 lb ai/acre), Sencor (0.5 lb ai/acre), Matrix (0.056 lb ai/acre), and Prowl plus Sencor. Outlook treatments were compared to combinations of Dual Magnum (.0 lb ai/acre) plus Prowl, Sencor, or Matrix, Prowl plus Sencor, and Prowl plus Eptam plus Sencor. Treatments were replicated three times. Matrix Combinations with New Herbicides for Weed Control in Potato Preemergence applications of Matrix at 0.04 lb ai/acre were applied alone and in combination with Outlook (0.656 lb ai/acre), Valor (0.094 lb ai/acre), Spartan (0.094 lb ai/acre), Sencor (0.5 lb ai/acre), and Dual Magnum (.0 lb ai/acre). Matrix plus methylated seed oil (MSO) (.0% v/v) were applied postemergence following preemergence applications of Outlook, Valor, and Spartan. Postemergence Matrix applications were inadvertently applied at one-third (0.008 lb ai/acre) of the desired rate on May, therefore a second application of 0.06 lb ai/acre was applied on May 0 to achieve the intended rate of 0.04 lb ai/acre. Treatments were replicated three times. Results and Discussion Weed Control with Valor and Spartan Rates Control of pigweed species (i.e., Powell amaranth and redroot pigweed) and common lambsquarters with Spartan treatments, Sencor plus Dual Magnum, and Matrix plus Dual Magnum was greater than with all Valor treatments on June 5 (4 days after treatment [DAT]) and August 6 (6 DAT) (Table ). Valor at 0.06 to 0.5 lb ai/acre provided hairy nightshade control ranging from 56 to 89 percent on June 5 compared to 00 percent control with all Spartan rates. However, on August 6 hairy nightshade control was similar with all Spartan rates and Valor at 0.5 lb ai/acre (9-99 percent). Valor at 0.5 lb ai/acre, Sencor plus Dual Magnum, and Matrix plus Dual Magnum provided similar hairy nightshade control on June 5. However, by August 6 hairy nightshade control was greater with Valor at 0.06, 0.094, and 0.5 (8-9 percent) than from either Sencor plus Dual Magnum or Matrix plus Dual Magnum( percent). Barnyardgrass control on June 5 was significantly less with Valor at 0.06 and lb ai/acre than from all other treatments. Total weed biomass was significantly greater with Valor treatments. In general, weed control increased with increasing Valor rates while weed control with Spartan was similar among rates. Based on weed biomass samples, there was a strong correlation between weed control and marketable potato yield (Fig. ). Total marketable potato yields ranged from 6 to 45 cwt/acre. Potato yields were significantly less with Valor treatments compared to all other treatments (Table ). Marketable potato yields with Spartan treatments were similar to Sencor plus Dual Magnum and Matrix plus Dual Magnum. Weed Control with Valor and Spartan Combinations Outlook and Spartan were the only single-product treatments that provided Powell amaranth and redroot pigweed, hairy nightshade, and common lambsquarters control similar to tank-mix treatments on June 5 (4 DAT) (Table ). On June 5, control of these weeds with Outlook was not significantly improved by the addition of Valor or Spartan. Similarly, weed control was not improved when Outlook, Dual Magnum, Prowl, or Eptam were applied with Spartan compared to Spartan alone. However, hairy nightshade control was significantly greater on August 6 (6 DAT) when Valor or Spartan Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85

147 were tank-mixed with Outlook, compared to Outlook alone. Prowl alone and Prowl plus Valor provided poor weed control on both evaluation dates. All treatments with either Valor or Spartan provided similar hairy nightshade control on August 6 (69-00 percent). When Outlook and Eptam were applied with Valor, barnyardgrass and hairy nightshade control were greater on June 5 and control of pigweed species and common lambsquarters were greater on June 5 and August 6 compared to Valor alone. Dual Magnum plus Valor provided greater pigweed, hairy nightshade, barnyardgrass, and common lambsquarters control on June 5 and greater pigweed control on August 6 compared to Valor alone. Outlook provided greater control of common lambsquarters than Dual Magnum, Prowl, Eptam, or Valor. Total weed biomass production was significantly less than the untreated check with Outlook alone and all tank-mix treatments except Valor plus Prowl. Hairy nightshade control was greater with all treatments including Spartan and the combination of Valor plus Outlook compared to Sencor plus Dual Magnum. Weed biomass samples indicated a strong correlation between weed control and marketable potato yield (Fig. ). Total marketable potato yields ranged from 65 to 479 cwt/acre (Table 4). Marketable yields increased when Outlook, Dual Magnum, or Eptam were applied with Valor compared to Valor alone. The addition of a tank-mix partner to Spartan did not provide greater U.S. No. or total marketable potato yields over those obtained with Spartan alone. Weed Control with Outlook Combinations Pigweed control was excellent (9 to 00 percent) with all treatments except Dual Magnum plus Prowl, which provided 6 and 5 percent control on June 5 (4 DAT) and August 6 (6 DAT), respectively (Table 5). Hairy nightshade control with Outlook plus Prowl H O was less on June 5 than from Outlook plus Sencor and Outlook plus Prowl plus Sencor. On August 6, Outlook plus Prowl provided significantly less hairy nightshade control than Outlook plus Sencor. All herbicide treatments provided greater common lambsquarters control than Dual Magnum plus Prowl on June 5 and August 6. On both evaluation dates, Outlook alone provided less common lambsquarters control than treatments including Sencor. Total weed biomass was greatest in plots treated with Dual Magnum plus Prowl and was not different from the untreated control. U.S. No. and total marketable potato yields were less with Dual Magnum plus Prowl than with all other treatments (Table 6). Marketable potato yields with Outlook plus Sencor, Outlook plus Prowl plus Sencor, and Prowl plus Sencor were greater than with Outlook alone. All Outlook treatment combinations provided similar U.S. No., U.S. No., total marketable, and total yields. Matrix Combinations with New Herbicides for Weed Control in Potato All treatments except Valor alone provided greater than 94 and 89 percent pigweed control on June 5 (4 DAT) and August 6 (6 DAT), respectively (Table 7). The combination of Matrix plus Valor provided 78 and 65 percent greater pigweed control compared to Valor alone on June 5 and August 6, respectively. Matrix plus Valor provided less hairy nightshade control compared with all other Matrix combinations on June 5. The combination of Matrix plus Sencor provided greater late-season (August 6) hairy nightshade and common lambsquarters control than either herbicide alone. Outlook applied with Matrix improved late-season hairy nightshade control by 69 percent over Matrix alone. Valor applied with Matrix improved late-season hairy nightshade control by 54 percent over Matrix alone. Matrix plus Valor controlled pigweed, barnyardgrass, and common lambsquarters better than Valor alone. Spartan applied with Matrix increased common lambsquarters control by 0 percent on June 5 and late-season hairy nightshade control by 59 percent compared to Matrix alone. Weed control was not different when Matrix (0.04 lb ai/acre) was applied preemergence with either Outlook or Spartan or when Matrix (0.008 followed by 0.06 lb ai/acre) was applied in sequential Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85

148 postemergence applications following preemergence applications of Outlook or Spartan. Preemergence Valor followed by sequential postemergence applications of Matrix provided greater hairy nightshade control on June 5 compared to the preemergence combination of Matrix plus Valor. Late-season common lambsquarters control was greater with the preemergence combination of Matrix plus Valor compared to the split /POST treatment of Valor followed by Matrix. Total weed biomass production was less than the untreated control with all preemergence Matrix combinations, the /POST treatment combinations of Outlook or Spartan followed by Matrix, and Outlook alone. Total marketable potato yields in herbicide-treated plots ranged from 9 to 45 cwt/acre. U.S. No. and total marketable potato yields were significantly greater than the untreated control with all herbicide treatments except Valor alone (Table 8). Total marketable potato yield with Matrix plus Valor was cwt/acre greater than from Valor alone. Table. Valor and Spartan rates for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed spp. Hairy nightshade Barnyard grass Common Lambsquarters Total weed biomass Treatment* Rate lb ai/acre % g/m Untreated check d f Valor c e Valor c d 8 69 Valor c c Valor b cd Spartan a a 97 6 Spartan a a 98 9 Spartan a a 00 0 Sencor + Dual Magnum b ab 98 6 Matrix + Dual Magnum b b 96 5 LSD (0.05) *Herbicide treatments were applied preemergence on May, 00. Pigweed species predominantly Powell amaranth mixed with some redroot pigweed. In columns where letter designations occur the ANOVA was performed on arcsine square root percent transformed data. Mean separations are applied to non-transformed data. Table. Valor and Spartan rates for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Potato yield U.S. No. Total Total Total Treatment* Rate 4-6 oz 6- oz > oz Total % No. marketable yield lb ai/acre cwt/acre % cwt/acre Untreated check Valor Valor Valor Valor Spartan Spartan Spartan Sencor + Dual Magnum Matrix + Dual Magnum LSD (0.05) *Herbicide treatments were applied preemergence on May, 00. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85

149 Figure. Response of marketable potato yields to total weed biomass (dry-weight basis). Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Table. Valor and Spartan combinations for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Weed control Pigweed Hairy Barnyard Common Total weed spp. nightshade grass Lambsquarters biomass Treatment* Rate lb ai/acre % g/m Untreated check d Outlook ab Dual Magnum ab Prowl ab Eptam ab Valor ab Spartan ab Valor + Outlook ab Spartan + Outlook ab Valor + Dual Magnum ab Spartan + Dual Magnum ab Valor + Prowl b Spartan + Prowl ab Valor + Eptam c Spartan + Eptam ab Sencor + Dual Magnum a LSD (0.05) *Herbicide treatments were applied preemergence on May, 00. Pigweed species were predominantly Powell amaranth mixed with some redroot pigweed. The ANOVA was performed on arcsine square root percent transformed data. Mean separations are applied to nontransformed data. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85

150 Table 4. Valor and Spartan combinations for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Potato yield U.S. No. Total Total Total Treatment* Rate 4-6 oz 6- oz > oz Total % No. marketable yield lb ai/acre cwt/acre % cwt/acre Untreated check Outlook Dual Magnum Prowl Eptam Valor Spartan Valor + Outlook Spartan + Outlook Valor + Dual Magnum Spartan + Dual Magnum Valor + Prowl Spartan + Prowl Valor + Eptam Spartan + Eptam Sencor + Dual Magnum LSD (0.05) *Herbicide treatments were applied preemergence on May, 00. Figure. Response of marketable potato yields to total weed biomass (dry-weight basis). Malheur Experiment Station, Oregon State University, Ontario, OR, 00. Malheur Experiment Station Annual Report 00. Oregon State University. Special Report 048. Pg. 7-85