WEED CONTROL AND CROP RESPONSE WITH HERBICIDES APPLIED IN FIELD CORN

Transcription

1 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, 2002 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 2:1 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 1:1 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-2398' (102 day relative maturity) field corn was planted with a John Deere model 71 Flexi Planter on May 7, Seed spacing was one seed every 7 inches on 30-inch rows. Plots were 10 by 30 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Plots were sidedressed with 80 lb N, 30 lb P, 4 lb Zn and Mn, 2 lb B, and 22 lb elemental S/acre on April 24. Herbicide treatments were applied with a CO 2-pressurized backpack sprayer calibrated to deliver 20 gal/acre at 30 psi. Crop response and weed control were evaluated throughout the growing season. Corn yield was determined by harvesting ears from 15-ft sections of the center two rows in each four-row plot on October 7-9. The 31

2 harvested ears were shelled and grain dry weight and percent moisture content were recorded. Grain yields were adjusted for a 12 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 (0.035 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 (1.0 lb ai/acre) or Dual II Magnum (1.6 lb ai/acre). Total postemergence Steadfast combinations were applied early postemergence on May 28. Steadfast combinations following preemergence applications were applied late postemergence on June 3. Steadfast combinations were compared to standard treatments including either Bicep II (2.5 lb ai/acre), Harness Xtra (3.0 lb ai/acre), or Harness (1.75 lb ai/acre), applied preemergence followed by Clarity (1.2 lb ai/acre) plus NIS (0.25 percent v/v) or preemergence Dual II Magnum (1.6 lb ai/acre) followed by Marksman (1.2 lb ai/acre) plus NIS. All postemergence treatments including Steadfast were applied with COC (1.0 percent v/v) plus AMS (2.0 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 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 1.0 oz ai/acre), or Distinct (1.4 oz ai/acre). Steadfast was applied postemergence at 0.56 oz ai/acre alone and in combinations with Callisto (1.0 oz ai/acre) or Distinct (1.4 oz ai/acre). Postemergence applications of DPX and Steadfast were applied with MSO (1.0 percent v/v) except for combinations including Callisto, which were applied with COC (1.0 percent v/v) or Distinct, which were applied with NIS (0.25 percent v/v). All postemergence applications included 32 percent N at 1.25 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 lb ai/acre to corn at the V2 growth stage on May 28. Option was applied alone and in combinations with Distinct (0.044, 0.087, and lb ai/acre), Callisto (0.047, 0.063, and lb ai/acre), Define (0.15, 0.225, and 0.3 lb ai/acre), Outlook (0.47 lb ai/acre), and Dual II Magnum (0.96 lb ai/acre). Treatments of Steadfast (0.035 lb ai/acre) plus Dual II Magnum and COC (1.25 percent v/v) or Callisto (0.063 lb ai/acre) were included for comparison. All treatments included 32 percent N at 1.25 percent v/v. 32

3 Broad Spectrum Weed Control with Dual II Magnum and Callisto Callisto was applied preemergence at lb ai/acre with Dual II Magnum (1.59 lb ai/acre) or Outlook (0.656 lb ai/acre). Callisto was applied postemergence at lb ai/acre alone, combined with Aatrex (0.25 lb ai/acre), or following preemergence applications of Dual II Magnum, Outlook, or Option (0.033 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 (0.175 lb ai/acre) plus NIS (0.25 percent v/v) and 28 percent N (2.5 percent v/v). All postemergence applications with Callisto included COC (1.0 percent v/v) and 28 percent N (0.25 percent v/v). Results and Discussion Preemergence Grass Herbicide Efficacy and Crop Safety Crop injury ranged from 3 to 10 percent on June 11 (14 and 8 days after early and late postemergence applications, respectively) (Table 1). The only herbicide treatments that resulted in less than 100 percent control of Powell amaranth and redroot pigweed on July 30 were treatments of Steadfast plus Distinct plus COC and AMS applied early postemergence following Dual II Magnum or Bicep II (Table 1). Barnyardgrass and green foxtail control on June 11 (8 and 14 days after late and early postemergence applications, respectively) was excellent (93 to 97 percent) with all Steadfast combinations. However, by July 30 (58 and 63 days after late and early postemergence applications, respectively), annual grass control was greatest in plots receiving preemergence applications of 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 30. Common lambsquarters control was 100 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 1). Weed Control with DPX and Steadfast Combinations Crop injury from herbicide treatment on June 11 (13 days after postemergence applications) ranged from 2 to 8 percent (Table 2). 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 11 and July 30, 34 and 83 days after preemergence applications, respectively. (Table 2). 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 30 (62 days after postemergence 33

4 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 11 and July 30. 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 18 and 12 percent, respectively on July 30. Postemergence Steadfast gave 12 percent greater control of Powell amaranth and redroot pigweed than DPX on July 30. 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 10 and 17 percent greater compared to DPX alone on June 11 and July 30, 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 30. DPX plus Aatrex controlled hairy nightshade 10 and 20 percent greater than DPX plus Distinct on June 11 and July 30, respectively. Postemergence DPX and Steadfast treatments gave similar hairy nightshade control on July 30. Despite poor (79 percent on June 11 and 54 percent on July 30) annual grass control, the postemergence treatment of Option plus Callisto resulted in the highest corn yield of 217 bu/acre (Table 2). 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 1.0 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 21 to 32 percent on June 4 (7 days after treatment [DAT]) and from 9 to 21 percent on June 11 (14 DAT) (Table 3). 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 (38 DAT). All herbicide treatments gave 95 percent or greater Powell amaranth and redroot pigweed control on June 11. Control of Powell amaranth and redroot pigweed on July 30 (63 DAT) was significantly (P < 0.05) improved over Option alone only when Callisto (0.063 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 11 than did treatments where Define was applied with Option. Hairy nightshade control ranged from 96 to 100 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 11. 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 0.15 to 0.3 lb ai/acre in a tank-mix with Option resulted in a 10 percent increase in annual grass control. Steadfast plus Callisto gave better annual grass control than did Option plus Callisto (0.063 lb ai/acre). 34

5 Corn yields in herbicide-treated plots ranged from 167 to 186 bu/acre and were greater than the untreated control. The combination of Option plus Distinct (0.175 lb ai/acre) provided greater yield than the treatment of Option plus Define (0.225 lb ai/acre), representing the only significant yield difference among herbicide treatments. Broad Spectrum Weed Control with Dual ll 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 2 (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 72 to 96 percent volunteer potato control on June 11 (14 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 < 0.1) increased volunteer potato control compared to Callisto alone (separation not shown). Corn yields in herbicide-treated plots were similar among treatments ranging from 184 to 207 bu/acre and were all greater than the untreated control. 35

6 Table 1. Weed control and yield with preemergence and postemergence herbicides in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed control Crop Common injury Pigweed spp. t Annual grass spp.t lambsquarters Corn Treatment Rate Timing* yield lb ai/acre % v/v Untreated control Bicep II Clarity + NIS % 2 Dual II Magnum Marksman + NIS % 2 Bicep II Steadfast Callisto Aatrex COC + AMS 1.0% Dual II Magnum Steadfast Callisto Aatrex COC + AMS 1.0% Bicep II Steadfast Distinct COC + AMS 1.0% Dual II Magnum Steadfast Distinct COC + AMS 1.0% Steadfast Callisto Aatrex COC + AMS 1.0% Harness Xtra Clarity + NIS % 2 bu/acre Harness Clarity + NIS % 2 LSD (0.05) "Application timings were (1) preemergence on , (2) early postemergence on , and (3) late postemergence on tpigweed species were predominantly Powell amaranth mixed with some redroot pigweed. *Annual grasses were predominantly barnyardgrass mixed with some green foxtail. 36

7 Table 2. Weed control and yield with DPX and Steadfast combinations in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed control Crop Annual grass Common Hairy injury Pigweed spp. t spilt lambsquarters nightshade Corn Treatment Rate Timing* yield oz ai/acre oho bu/acre % v/v Untreated control Dual II Magnum 20.8 PRE cd 152 DPX PRE cd 161 DPX PRE c 181 Callisto 4.0 DPX POST ab 198 MS0 + 32% N % DPX POST a 215 Aatrex MS0 + 32% N % DPX POST ab 199 Callisto DPX POST a 197 Callisto Aatrex DPX POST ab 206 Callisto DPX POST ab 207 Callisto Aatrex DPX POST b 207 Distinct NIS + 32% N % Steadfast POST ab 180 MS0 + 32% N % Steadfast POST ab 190 Callisto Steadfast POST ab 203 Distinct NIS + 32% N % Option POST ab 217 Callisto COC + 32% N % LSD (0.05) *Herbicide treatments were applied preemergence (PRE) on and postemergence (POST) on tpigweed 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 non-transformed data. 37

8 Table 3. Weed control, crop response, and yield with postemergence Option combinations in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed control Crop Common Hairy Vol. Annual injury Pigweed spp. t lambsquarters nightshade potato grass spp.t Corn Treatment* Rate yield lb ai/acre % bu/acre % v/v Untreated control f 90 Option * de 170 Option b-e 184 Distinct Option de 184 Distinct Option de 186 Distinct Option de 171 Callisto Option Callisto Option cde 183 Callisto Option de 171 Define Option a-d 167 Define Option ab 168 Define Option ab 175 Outlook Option a 177 Dual II Magnum Steadfast abc 177 Dual II Magnum COC + 32% N % Steadfast a-d 184 Callisto LSD (0.05) *Herbicide treatments were applied postemergence to corn at the V2 growth stage on tpigweed 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. 38

9 Table 4. Weed control and yield with Dual II Magnum and Callisto in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed controls Crop Common Hairy Annual Vol. injury Pigweed spp. t Lambsquarters nightshade grass spp. potato Corn Treatment Rate Timing* yield lb ai/acre % v/v bu/acre Untreated control e d Dual II Magnum cd ab Callisto Callisto a c Dual II Magnum a a Callisto Aatrex Outlook d be Callisto Outlook a ab Callisto Callisto a ab Aatrex COC + AMS Outlook a a Callisto Aatrex Option ab ab Callisto Dual II Magnum be ab Distinct NIS % 2 28% N 2.5% 2 LSD (0.05) *Herbicide treatments were applied (1) preemergence on and (2) postemergence to corn at the V2 growth stage on tin columns where letter designations occur, the ANOVA was performed on arcsine square root percent transformed data. Mean separations were applied to non-transformed data. tpigweed was predominantly Powell amaranth mixed with some redroot pigweed. Annual grass species were predominantly barnyardgrass mixed with some green foxtail. 39