,4nnual Report Special Report Oregon State. DOES NOT CIRCULATE Oregon State University. Received on: Special report.

Transcription

1 Special Report 17 July 26 5 E55 Experiment Station,4nnual Report 25 Oregon State UNIVERSITY Agricultural ExperimentStation DOES NOT CIRCULATE Oregon State University Received on: Special report

2 For additional copies of this publication Clinton C. Shock, Superintendent Malheur Experiment Station 595 Onion Avenue Ontario, OR For additional information, please check our website

3 Agricultural Experiment Station Oregon State University Special Report 17 July26 Maiheur Experiment Station Annual Report 25 The information in this report is for the purpose of informing cooperators in industiy, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should information and interpretation thereof be considered as recommendations for application ofany pesticide. Pesticide labels should always be consulted before any pesticide use. Common names and manufacturers of chemical products used in the trials reported here are contained in Appendices A and B. Common and scientific names of crops are listed in Appendix C. Common and scientific names of weeds are listed in Appendix D. Common and scientific names of diseases and insects are listed in Appendix E.

4 CONTRIBUTORS AND COOPERATORS MALHEUR EXPERIMENT STATION SPECIAL REPORT 25 RESEARCH MALHEUR COUNTY OFFICE, OSU EXTENSION SERVICE PERSONNEL Jensen, Lynn Professor Moore, Marilyn Instructor Norberg, Steve Assistant Professor Porath, Marni Assistant Professor MALHEUR EXPERIMENT STATION Eldredge, Eric Faculty Research Assistant Feibert, Erik Senior Faculty Research Assistant Ishida, Joey Bioscience Research Technician Jones, Janet Office Specialist Pereira, Andre Visiting Professor Ransom, Corey V. Assistant Professor of Weed Science Saunders, Lamont Bioscience Research Technician Shock, Clinton C. Professor, Superintendent MALHEUR EXPERIMENT STATION, STUDENTS Flock, Rebecca Research Aide Ishida, Jessica Research Aide Linford, Christie Research Aide Montgomery, Stephanie Research Aide Noble, Heather Research Aide Ransom, Christopher Research Aide Rhoades, Josh Research Aide Shock, Cedric Research Aide Sullivan, Susan Research Aide OREGON STATE UNIVERSITY, CORVALLIS, AND OTHER STATIONS Bafus, Rhonda Faculty Research Assistant, Madras Bassinette, John Senior Faculty Research Assistant, Dept. of Crop and Soil Science Charlton, Brian Faculty Research Assistant, Kiamath Falls Hane, Dan Potato Specialist, Hermiston James, Steven Senior Research Assistant, Madras Karow, Russell Professor, Dept. of Crop and Soil Science Locke, Kerry Associate Professor, Klamath Falls Mosley, Alvin Associate Professor, Dept. of Crop and Soil Science Rykbost, Ken Professor, Superintendent, Kiamath Falls

5 OTHER UNIVERSITIES Brown, Bradford Gallian, John Hoffman, Angela Hutchinson, Pamela Love, Steve Mohan, Krishna Morishita, Don Neufeld, Jerry Nissen, Scott Novy, Rich O'Neill, Mick Reddy, Steven Associate Professor, Univ. of Idaho, Parma, ID Professor, Univ. of Idaho, Twin Falls, ID Professor, Univ. of Portland, Portland, OR Assistant Professor, Univ. of Idaho, Aberdeen, ID Professor, Univ. of Idaho, Aberdeen, ID Professor, Univ. of Idaho, Parma, ID Associate Professor, Univ. of Idaho, Twin Falls, ID Associate Professor, Univ. of Idaho, CaIdwell, ID Associate Professor, Colorado State Univ., Ft. Collins, CO Research Geneticist/Potato Breeder, USDA, Aberdeen, ID Superintendent, New Mexico State Univ., Farmington, NM Extension Educator, Univ. of Idaho, Weiser, ID OTHER PERSONNEL COOPERATING ON SPECIAL PROJECTS Anderson, Brian Clearwater Supply, Inc., Othello, WA Bosshart, Perry Professional Research Consultant, Farmington, ME Camp, Stacey Amalgamated Sugar Co., Paul, ID De Bolt, Ann USDA Forest Service, Boise, ID Delin, Kevin NASA Jet Propulsion Laboratory, Pasadena, CA Eaton, Jake Potlatch, Boardman, OR Erstrom, Jerry Malheur Watershed Council, Ontario, OR Feuer, Lenny Automata, Inc., Nevada City, CA Futter, Herb Malheur Owyhee Watershed Council, Ontario, OR Hansen, Mike M.K. Hansen Co., East Wenatchee, WA Hawkins, Al Irrometer Co., Inc., Riverside, CA Hill, Carl Owyhee Watershed Council, Ontario, OR Huffacker, Bob Amalgamated Sugar, Nyssa, OR Jones, Ron Oregon Department of Agriculture, Ontario, OR Kameshige, Brian Cooperating Grower, Ontario, OR Kameshige, Randy Cooperating Grower, Ontario, OR Klauzer, Jim Clearwater Supply, Inc., Ontario, OR Komoto, Bob Ontario Produce, Ontario, OR Leiendecker, Karen Oregon Watershed Enhancement Board, La Grande, OR Lund, Steve Amalgamated Sugar Co., Twin Falls, ID Martin, Jennifer Coordinator, Owyhee Watershed Council, Ontario, OR Matson, Robin Englehard Corp., Yakima, WA McKelIip, Robert Cooperating Grower, Nampa, ID Mittlestadt, Bob Clearwater Supply, Inc., Othello, WA Murata, Warren Cooperating Grower, Ontario, OR Nakada, Vernon Cooperating Grower, Ontario, OR Nakano, Jim Maiheur Watershed Council, Ontario, OR Page, Gary Malheur County Weed Supervisor, Vale, OR Penning, Tom Irrometer Co., Inc., Riverside, CA Petersen, Ed Natural Resource Conservation Service, Ontario, OR Phillips, Lance Soil and Water Conservation District, Ontario, OR Pogue, Bill Irrometer Co., Inc., Riverside, CA Polhemus, Dave Andrews Seed Co., Ontario, OR

6 OTHER PERSONNEL COOPERATING ON SPECIAL PROJECTS (continued) Richardson, Phil Oregon Dept. of Environmental Quality, Pendleton, OR Shaw, Nancy USDA Forest Service, Boise, ID Simantel, Gerald Novartis Seed, Longmont, CO Stadick, Chuck Simplot Grower Solutions, CaIdwell, ID Stander, J. R. Betaseed, Inc., Kimberly, ID Stewart, Kevin T-Systems International, Kennewick, WA Taberna, John Western Laboratories, Inc., Parma, ID Vogt, Glenn J. R. Simplot Co., Caldwell, ID Wagstaff, Robert Cooperating Grower, Nyssa, OR Weidemann, Kelly Malheur Watershed Council, Ontario, OR Yoder, Ron DuPont Crop Protection, Boise, ID GROWERS ASSOCIATIONS SUPPORTING RESEARCH Idaho-Eastern Oregon Onion Committee Idaho Mint Commission Malheur County Potato Growers Nyssa-Nampa Beet Growers Association Oregon Alfalfa Seed Commission Oregon Alfalfa Seed Growers Association Oregon Potato Commission Oregon Wheat Commission PUBLIC AGENCIES SUPPORTING RESEARCH Agricultural Research Foundation Oregon Department of Agriculture Oregon Department of Environmental Quality Oregon Watershed Enhancement Board U.S. Environmental Protection Agency 319 Program USDA Cooperative State Research, Education, and Extension Service USDA Forest Service Western Sustainable Agriculture Research and Extension

7 COMPANY CONTRIBUTORS ABI Alfalfa, Inc. Advanced Agri-Tech Allied Seed Cooperative American Crystal Sugar Co. American Takii, Inc. AMVAC BAS F Bayer CropScience Bejo Seeds, Inc. Betaseed, Inc. Clearwater Supply, Inc. Crookham Co. D. Palmer Seed Co., Inc. Dairyland Research DeKaIb Genetics Corp. Dorsing Seeds, Inc. Dow Agrosciences DuPont ESI Environmental Sensors FMC Corp. Forage Genetics Fresno Valves & Castings, Inc. Geertson Seed Co. Global Genetics Gowan Co. Holly Sugar Corp. Irrometer Co., Inc. M.K. Hansen Co. Monsanto Nelson Irrigation Netafim Irrigation, Inc. Nichino America, Inc. Novartis Seeds, Inc. Nunhems USA, Inc. Pioneer Potlatch Rispens Seeds, Inc. Rohm and Haas Sakata Seed America Scottseed Seed Systems Seed Works Seedex, Inc. Seminis Vegetable Seeds, Inc. Simplot Co. Summerdale, Inc. Syngenta T-Systems International UAP Northwest Valent W-L Research

8 TABLE OF CONTENTS WEATHER 25 Weather Report I ALFALFA Alfalfa Seed Quality Favored by Water Stress 9 CORN Weed Control and Crop Response with Option and Impact Herbicides in Furrow-irrigated Field Corn - 27 MINT Evaluations of Spring and Fall Herbicides for Peppermint 33 NATIVE PLANT SEED PRODUCTION Identification of Herbicides for Use in Native Forb Seed Production 35 Subsurface Drip Irrigation for Native Forb Seed Production 39 ONION 25 Onion Variety Trials 42 Evaluation of Over-wintering Onion for Production in the Treasure Valley - 24/25 Trial 54 Onion Production From Sets 58 Onion Production From Field-grown Transplants 64 Automatic Collection, Radio Transmission, and Use of Soil Water Data 68 Short-duration Water Stress Decreases Onion Single Centers Without Causing Translucent Scale 8 Insecticide Trials for Onion Thrips (Thrips tabaci) Control A Three-year Study on Varietal Response to an Alternative Approach for Controlling Onion Thrips (Thrips tabaci) in Spanish Onions 99 A One-year Study on the Effectiveness of Vydate L (Oxamyl) to Control Thrips in Onions When Injected into a Drip-irrigation System 19 Preemergence and Postemergence Combinations for Weed Control in Onion Soil-active Herbicide Applications for Weed Control in Onion 122 Comparison of Goal 2XL and Goal Tender for Crop Injury and Weed Control in Onion 126 The Effectiveness of Root Feed II and STO-5 for Onion Production When Injected into a Drip-irrigation System 129

9 TABLE OF CONTENTS (continued) POPLARS Performance of Hybrid Poplar Clones on an Alkaline Soil 134 Micro-irrigation Alternatives for Hybrid Poplar Production, 25 Trial 139 Effect of Pruning Severity on the Annual Growth of Hybrid Poplar 152 POTATO Potato Variety Trials Effect of Irrigation Systems and Cultural Practices on Potato Performance 177 Evaluation of Alternative Carriers for Potato Seed Treatment Fungicides 187 Development of New Herbicide Options for Weed Control in Potato Production RANGELAND WEED MANAGEMENT Control of Perennial Pepperweed and Russian Knapweed with Habitat and Plateau Herbicides 198 SOYBEAN Soybean Performance in Ontario in Organic Soybean Production in Ontario in SUGAR BEETS Sugar Beet Variety Trials Kochia Control with Preemergence Nortron in Standard and Micro-rate Herbicide Programs in Sugar Beet 217 Comparison of Calendar Days and Growing Degree Days for Scheduling Herbicide Applications in Sugar Beet 222 TEFF Teff (Era grostis tef), an Irrigated Warm Season Annual Forage Crop 227 Overseeding Teff (Era grostis tef) into Alfalfa 234 WHEAT AND SMALL GRAINS 25 Winter Elite Wheat Trial 238 Water Management for Drip-irrigated Spring Wheat 241 YELLOW NUTSEDGE BIOLOGY AND CONTROL Eptam for Yellow Nutsedge Supression on Idle Land 248 Preliminary Investigations of Royal MH-3 Effects on Yellow Nutsedge Dormancy 25

10 TABLE OF CONTENTS (continued) APPENDICES A. Herbicides and Adjuvants 252 B. Insecticides, Fungicides, and Nematicides 253 C. Common and Scientific Names of Crops, Forages, and Forbs 254 D. Common and Scientific Names of Weeds 255 E. Common and Scientific Names of Diseases and Insects 255

11 25 WEATHER REPORT Erik B. G. Feibert and Clinton C. Shock Malheur Experiment Station Oregon State University Ontario, OR Introduction Air temperature and precipitation have been recorded daily at the Maiheur Experiment Station since July 2, Installation of additional equipment in 1948 allowed for evaporation and wind measurements. A soil thermometer at 4-inch depth was added in A biophenometer, to monitor degree days, and pyranometers, to monitor total solar and photosynthetically active radiation, were added in Since 1962, the Malheur Experiment Station has participated in the Cooperative Weather Station system of the National Weather Service. The daily readings from the station are reported to the National Weather Service forecast office in Boise, Idaho. Starting in June 1997, the daily weather data and the monthly weather summaries have been posted on the Maiheur Experiment Station web site on the Internet at On June 1, 1992, in cooperation with the U.S. Department of the Interior, Bureau of Reclamation, a fully automated weather station, linked by satellite to the Northwest Cooperative Agricultural Weather Network (AgriMet) computer in Boise, Idaho, began transmitting data from Malheur Experiment Station. The automated station continually monitors air temperature, relative humidity, dew point temperature, precipitation, wind run, wind speed, wind direction, solar radiation, and soil temperature at 8-inch and 2-inch depths. Data are transmitted via satellite to the Boise computer every 4 hours and are used to calculate daily Maiheur County crop water-use estimates. The AgriMet database can be accessed through the internet at and is linked to the Malheur Experiment Station web page at Methods The ground under and around the weather stations was bare until October 17, 1997, when it was covered with turfgrass. The grass is irrigated with subsurface drip irrigation. The weather data are recorded each day at 8: a.m. Consequently, the data in the tables of daily observations refer to the previous 24 hours. Evaporation is measured from April through October as inches of water evaporated from a standard class A pan (1-inch-deep by 4-ft-diameter) over 24 hours. Evapotranspiration (EL) for each crop is calculated by the AgriMet computer using data from the I

12 AgriMet weather station and the Kimberly-Penman equation (Wright 1982). Reference evapotranspiration (ET) is calculated for a theoretical 12- to 2-inch-tall crop of alfalfa assuming full cover for the whole season. Evapotranspiration for all crops is calculated using ET and crop coefficients for each crop. These crop coefficients vary throughout the growing season based on the plant growth stage. The crop coefficients are tied to the plant growth stage by three dates: start, full cover, and termination dates. Start dates are the beginning of vegetative growth in the spring for perennial crops or the emergence date for row crops. Full cover dates are typically when plants reach full foliage. Termination dates are defined by harvest, frost, or dormancy. Alfalfa mean is calculated for an alfalfa crop assuming a 15 percent reduction to account for cuttings. Wind run is measured as total wind movement in miles over 24 hours at 24 inches above the ground. Weather data averages in the tables, except evapotranspiration, refer to the years preceding and up to, but not including, the current year. 25 Weather The total precipitation for 25 (14.25 inches) was higher than the 1-year (1.38 inches) and 6-year (1.19 inches) averages (Table 1). Precipitation in May (2.94 inches) was over twice as high as the 1-year and 6-year averages and was the third highest since observations began in 1943 (1st: 4.55 inches in May 1998, 2nd: 3.9 inches May 1953). The months of October, November, and December had precipitation higher than average. Precipitation in December (3.92 inches) was over twice as high as the 1-year and 6-year averages and was the highest since observations began in Total snowfall for 25 (14 inches) was lower than the 1-year (14. inches) and 62-year averages (18.2 inches) (Table 2). The highest temperature for 25 was 11 F on August 6 and 7 (Table 3). The lowest temperature for the year was -2 F on December 18. The average maximum and minimum air temperatures for December were substantially lower than the 1-year and 6-year averages. The months of April, May, and June had a lower number of growing degree days (5 to 86 F) than the 19-year average (Table 4, Fig. 1). June had 19 percent fewer growing degree days than the 19-year average. The total number of degree days in the aboveoptimal range in 25 was close to the average (Table 5). All months, except April, had total wind runs lower than the 1-year and 57-year averages (Table 6). Total pan-evaporation for 25 was close to the 1-year and 56-year averages (Table 7). Total accumulated for all crops in 25 was close to the 14-year average (Table 8). The average monthly maximum and minimum 4-inch soil temperatures in 25 were close to the 1-year and 37-year averages (Table 9). 2

13 The last spring frost (32 F) occurred on April 15, 13 days earlier than the 29-year average date of April 28; the first fall frost occurred on October 6, 1 day later than the 29-year average date of October 5 (Table 1). No other weather records were broken in 25 (Table 11). References Wright, J.L New evapotranspiration crop coefficients. J. Irrig. Drain. Div., ASCE 18: Table 1. Monthly precipitation at the Malheur Experiment Station, Oregon State University, Ontario, OR, Year - Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 1991 inches yravg yravg Table 2. Annual snowfall totals at the Malheur Experiment Station, Oregon State University, Ontario, OR, yr 62-yr avg avg inches

14 Table 3. Monthly air temperature, Maiheur Experiment Station, Oregon State University, Ontario. OR, 25. Jan Max Mm Feb Max Mm Mar Max Mm Apr Max Mm May Max Mm Jun Max Mit, Jul Max Mm Aug Max Mm Sep Max Mm Oct Max Mm Nov Max Mm Dec Max Mm Highest Lowest avg yr avg yr avg U- ( co U) Ci) >' ) C) ) ) >.1-' E Average Day of year Figure 1. Cumulative growing degree days (5-86 F) over time for selected years compared to 15-year average, Maiheur Experiment Station, Oregon State University, Ontario, OR. 4

15 Table 4. Monthly total growing degree days (5-86 F), Malheur Experiment Station, Oreqon State University, Ontario, OR, Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total , , , , , , , , , , , , , , , yearavg ,92 Table 5. Monthly total degree days in the above-ideal ( F) range, Malheur Station, Oregon State University, Ontario. OR Year Apr May Jun Jul Aug Sep Oct Total yr avg

16 Table 6. Wind-run daily totals and monthly totals, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Daily Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec miles Mean Max Mm Annual total ,831 2,214 1,295 1,296 1,264 1,276 1, , yraverage 1,521 1,813 2,375 2,415 2,23 1,897 1,71 1,62 1,524 1,655 1,549 1, yraverage 2,152 1,926 1,568 1,47 1,327 1,255 1,284 miles Table 7. Pan-evaporation totals, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Totals April May Jun Jul Aug Sep Oct Total Daily inches Mean Max Mm Annual inches yravg yravg

17 Table 8. Total accumulated reference evapotranspiration (ET) and crop evapotranspiration (ETa) (acre-inches/acre), Mal heu r Experiment Station, Oregon State University, Ontario, OR, Year ET Alfalfa Winter Spring Sugar. Dry Field.. Onions (mean) Potatoes grain grain beets beans corn st year Poplar 2nd year 3rd year Average mm 1,4.5 1, ,145.5 Table 9. Monthly soil temperature at 4-inch depth, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm Max Mm F Highest Lowest avg yr avg yr avg

18 Table 1. Last and first frost (32 F) dates and nurnber of frost-free days, Maiheur Experiment Station, Oregon State University, Ontario, OR, Year Date of last frost, Spring Date of first frost Fall Total frost-free days 199 May8 Oct Apr3 Oct Apr24 Sep Apr2 Oct Apr15 Oct Apr16 Sep May6 Sep May3 Oct Apr18 Oct May11 Sep May12 Sep Apr29 Oct May8 Oct May19 Oct April16 Oct April15 Oct Avg April 28 October 5 Table 11. Record weather events at the Maiheur Experiment Station, Oregon State University, Ontario, OR. Record event Greatest annual precipitation Since 1943 Measurement Date inches 1983 Greatest monthly precipitation 4.55 inches May 1998 Greatest 24-hour precipitation 1.52 inches Sep 14, 1959 Greatest annual snowfall 4 inches 1955 Greatest 24-hour snowfall 1 inches Nov 3, 1975 Earliest snowfall 1 inch Oct 25, 197 Highest air temperature 11 F July 22, 23 Total days with maximum air temp. 1 F 17 days 1971 Lowest air temperature -26 F Jan 21 and 22, 1962 Total days with minimum air temp. F Lowest soil temperature at 4-inch depth Highest yearly growing degree days Lowest yearly growing degree days Highest reference evapotranspiration Since 1967 Since 1986 Since 1992 days F Dec 24, 25, and 26, 199 3,446 degree days ,539 degree days inches 22 8

19 ALFALFA SEED QUALITY FAVORED BY WATER STRESS Clinton C. Shock, Erik B.G. Feibert, and Lamont D. Saunders Malheur Experiment Station, Oregon State University Jim Klauzer Clearwater Supply Ontario, OR Sum mary Two alfalfa varieties ('Tango' and 'Accord') were grown for seed using subsurface drip irrigation with four evapotranspiration (EL) replacement levels: 8, 6, 4, and 2 percent of the accumulated water needs. After the start of flowering the alfalfa was irrigated every 3-4 days at the corresponding replacement level. Over the 3 years seed quality was maximized at 2 to 3 percent of replacement level, but seed yield was maximized by 4 to 5 percent replacement level. Seed quality at 4 to 5 percent replacement was above certification standards each year. The results suggest that alfalfa seed production can be maximized with 4 to 5 percent replacement using drip irrigation. Introduction In the 198's, research at the Maiheur Experiment Station with furrow-irrigated alfalfa demonstrated that water stress was associated with high alfalfa seed yields (Shock et al. 199). There is a strategic balance between the amount of water needed to sustain growth and productivity and water stress sufficient for the alfalfa plant to remain reproductive rather than vegetative. Achieving uniform water stress along the entire length of the field with furrow irrigation is problematic because water application is not uniform. Alfalfa in areas of the field where more water soaks into the soil remains vegetative, while alfalfa in dry areas can become excessively stressed. Subsurface drip irrigation can be used to apply water more uniformly, allowing for more uniform water stress. Subsurface drip irrigation also has environmental benefits compared to furrow irrigation, due to 1) more efficient water use, 2) reduction of deep percolation of water, and 3) elimination of runoff losses of water and nutrients. Since uniform water stress along the whole field length is feasible with drip irrigation, accurate irrigation management becomes important. The purpose of this experiment was to determine the level of deficit irrigation that optimizes alfalfa seed quality and yield. 9

20 Materials and Methods Establishment Procedures Alfalfa was grown for seed on a Nyssa silt loam of modest fertility (ph of 7.8, 1.5 percent organic matter [OM]) and field history of modest productivity. The site was chosen to be representative of fields used for alfalfa seed production. The field was previously planted to wheat. Two varieties of alfalfa were planted on April 6, 2 at 2 lb/acre in 3-inch rows. Tango, with a dormancy rating of six was planted in the upper half of the field and Accord, with a dormancy of four was planted in the lower half of the field. The alfalfa was irrigated with drip tape (T-Tape TSX ) buried at 12-inch depth between two alfalfa rows. The drip tape was buried on alternating inter-row spaces (5 ft apart). The flow rate for the drip tape was.34 gal/miniloo ft at 8 PSI with emitters spaced 16 inches apart, resulting in a water application rate of.66 inch/hour. In 2, the year of establishment, the field was irrigated uniformly the whole season. The seed was harvested with a commercial combine. In early March of each of the following years, the field was cultivated with a triple-k and Prowl at 3.3 lb ai/acre was broadcast. The alfalfa was flailed (clipped back just above ground level) on May 3, 21 and 22, and on May 1, 23 to delay flowering until air temperature was adequate for leafcutter bee activity. Alfalfa leafcutting bee (Megachi!e ratundata) populations were maintained at standard levels using four houses with nesting boards at the center of each field edge. Alfalfa Irrigation The following irrigations were applied to all plots before flowering: 2 inches on May 23 and June 1, 21; 2 inches on May 17, May 3, and June 6,22; and 2 inches on May23 and June 2,23. Flower bud break started on June 1,21, June 15, 22, and June 7, 23. After the start of flowering, the alfalfa was irrigated at four levels of alfalfa crop evapotranspiration (EL) replacement (2, 4, 6, and 8 percent) with five replicates of each treatment (Table 1). Each treatment was irrigated every 3-4 days. The amount of water to be applied to each treatment at each irrigation was calculated as the respective percentage of the difference between the accumulated and the accumulated amount of irrigation water plus precipitation applied. Both and irrigation water plus precipitation were accumulated from the start of flowering. Irrigations were terminated on August 21, 21, August 15, 22, and August 7, 23. Each plot consisted of eight alfalfa rows spaced 3 inches apart, 48 ft long, with two subplots corresponding to the two alfalfa varieties. Each plot was irrigated separately by its own pressure regulator, electronic solenoid valve, and water meter. Water meters were read before and after each irrigation. Alfalfa was calculated with a modified Penman equation (Wright 1982) and peak alfalfa crop coefficients using data collected at the Malheur Experiment Station by an AgriMet weather station (U.S. Bureau of Reclamation, Boise, ID) adjacent to the field. The was estimated and recorded from dormancy break until the final irrigation. Dormancy break occurred on March 1, 21, March 26, 22, and March 1, 23. 1

21 After the alfalfa was flailed, the adjusted using crop cover. The crop cover was derived from weekly measurements of the percent ground cover until full cover was achieved. Full cover was achieved by mid- to late May, before flowering. Determination of Soil Water Content Soil volumetric water content was determined by soil moisture sensors (Environmental Sensors Inc., Victoria, British Columbia, Canada). The Gro-Point sensors use TDT (Time Domain Transmissometry) technology to measure soil moisture. One Gro-Point sensor was installed at 12-inch depth and one at 2-inch depth in each plot. The Gro-Point sensors were installed horizontally halfway between the drip tape and the alfalfa row in the plot center. Sensors were located 7 ft from the center of the field in the Tango subplots. Sensors were connected by buried cables to electronic communication boards housed in two locations in the field. The electronic communication boards were connected by a cable to a personal computer in the station office, allowing the soil water content to be read and logged every hour. Soil volumetric water content was also measured with a neutron probe to verify moisture readings from the Gro-Point sensors. One access tube was installed in each plot halfway between the drip tape and the alfalfa row in the plot center. The neutron probe access tubes were located 15 ft from the center of the field in the Tango subplots. Neutron probe readings were made twice weekly at the same depths as the Gro-Point sensors. The neutron probe was calibrated by taking soil samples and probe readings at 12-inch and 2-inch depths during installation of the access tubes. The soil water content was determined gravimetrically from the soil samples and regressed against the neutron probe readings, separately for each soil depth. The regression equations were then used to transform the neutron probe readings during the season into volumetric soil water content. Regression equations were: Y = X (R2 =.86, P =.1)for the 12-inch depth, and Y = X (R2 =.96, P =.1) for the 2-inch depth, where X = 32-second neutron probe counts and Y = percent soil volumetric water content. Volumetric water content measured by the Gro-Point sensors was adjusted to volumetric water content measured by neutron probe using regression equations for each depth separately (Fig. 1). Lygus Bug Monitoring and Control Lygus bugs (Lygus hesperus) were monitored twice weekly by taking three 18 sweeps with an insect net in each plot. The total numbers of early and late lygus instars and lygus adults in each sweep were determined. When the total number of lygus (early and late instars, and adults), averaged over all plots, reached four per sweep, insecticides were applied. The insecticides were of short longevity and were applied in the late evening to minimize adverse effects on the Leafcutting bees. The timing of insecticide applications was affected by wind and commercial application spraying schedules. Alfalfa Biomass Yields Biomass samples were taken in each subplot by cutting the plants at ground level in 3.3 ft of one row on August 6, August 22, and August 19, in 21, 22, and 23, 11

22 respectively. The samples were weighed, oven dried, and weighed again. The dried samples were separated into stems, leaves, and seed pods. The separated samples were oven dried and weighed. Alfalfa Seed Yield and Quality The alfalfa was desiccated with Boa (Paraquat dichloride) at.63 lb ai/acre plus Reglone (Diquat) at.5 lb ai/acre on August 29 each year. On September 5, 21, September 9, 22, and September 12, 23, 66 ft of each subplot was harvested with a small-plot combine (52-inch width). The harvested seed was cleaned and weighed. A 4-seed sample was taken from each subplot and analyzed for germination, hard seed, abnormal seed, and dead seed by the Oregon State University Seed Laboratory. Seed size was determined by weighing a 54-seed sample from each subplot. Data were analyzed using analysis of variance (General Linear Models procedure) and regression (Response Surface Analysis) from NCSS software (NCSS, Kaysville, UT). Results and Discussion Differential Irrigation The total from dormancy break to the onset of flowering was 11.7, 1.1, and 11.4 inches in 21, 22, and 23, respectively. The total amount of water applied plus precipitation from dormancy break to the onset of flowering was 6.2, 6.9, and 7.6 inches in 21, 22, and 23, respectively. There were small differences between treatments in the average soil volumetric water content during the period from clipback to the onset of flowering (Table 1). These differences were unrelated to the treatments. The average soil volumetric water content was higher during the pre-flowering period than the post-flowering period for the 2 percent, 4 percent, and 6 percent replacements. For the 8 percent replacement, the average soil volumetric water content was close to or lower during the pre-flowering period than the post-flowering period. The total from the onset of flowering to the end of August was 25.1, 25.1, and 26.& inches in 21, 22, and 23, respectively. The total from dormancy break to the end of August was 37.9, 35.3, and 38.2 inches in 21, 22, and 23, respectively. After the start of flowering, the treatments were clearly differentiated in terms of the total amount of water applied and the actual percent of replaced (Table 1). The treatments followed fairly closely the experimental plan. Each year, there was a significant trend for increasing average soil volumetric moisture content with increasing replacement (Table 1). 12

23 Alfalfa Seed Quality The response of seed quality to replacement was similar for the two varieties. There was a trend for increasing germination with decreasing replacement each year (Table 2, Fig. 2). There was a trend for increasing germination plus hard seed with decreasing replacement in 21 and 22, but not in 23 (Table 2, Fig. 3). There was a trend for increasing abnormal plus dead seed with increasing replacement in 21 and 22, but not in 23 (Table 2, Fig. 4). There was a trend for increasing seed size with increasing replacement each year (Table 2, Fig. 5). Alfalfa Biomass and Seed Yields The response of biomass dry yield, seed pod dry weight percentage, seed pod yield, and seed yield to replacement was similar for the two varieties. There was a trend for increasing biomass dry yield with increasing replacement each year (Table 2, Fig. 6). Averaged over years and varieties, seed pod dry weight as a proportion of the whole plant dry weight was highest with either 4 or 6 percent replacement (Table 2, Fig. 7). Averaged over years and varieties, seed pod yield was highest with 6 percent replacement (Table 2, Fig. 8). Averaged over years and varieties, seed yield was highest with either 4 percent or 6 percent replacement (Table 2, Fig. 9). Calculated from the regression equations, maximum' seed pod yield was achieved with 46 percent, 57 percent, and 6 percent replacement in 21, 22, and 23, respectively (Fig. 8). Averaged over the 3 years, seed pod yield was highest with 55 percent replacement. Calculated from the regression equations, maximum seed yield was achieved with 4 percent, 51 percent, and 67 percent replacement in 21, 22, and 23, respectively (Fig. 9). Averaged over the 3 years, seed yield was highest with 5 percent replacement (Fig. 9). Calculated from the regression equations, maximum seed pod dry weight percentage was achieved with 22 percent, 49 percent, and 45 percent replacement in 21, 22, and 23, respectively (Fig. 7). Averaged over the 3 years, seed pod dry weight percentage was highest with 44 percent replacement. Conclusion The increasing water deficit from the irrigation treatments caused the alfalfa plants to shift from higher vegetative growth to more reproductive growth, with the highest reproductive growth at a moderate level of water stress. Highest seed pod dry weight percentage, seed yield, and seed pod yield were achieved with 44, 5, and 55 percent replacement, respectively. Highest seed quality (highest germination and lowest defective seed) was achieved with 2 to 3 percent replacement. The alfalfa seed size decrease with decreasing replacement was more pronounced below about 5 to 6 percent ETC. replacement. For certification purposes, alfalfa seed must have a minimum germination plus hard seed of 85 percent in Oregon. Each year and averaged over the 3 years, calculated germination plus hard seed for a 5 percent replacement was close to or higher than 85 percent. This suggests that alfalfa seed 13

24 production can be optimized at 4 to 5 percent replacement. An replacement of 4 to 5 percent would maximize seed yield without reducing seed quality below certification standards and would maintain larger seed sizes. References Shock, C.C., T. Stieber, B. Stephen, V. Cairo, L. Saunders, B. Gardner, A. Bibby, and D. Tipton Water stress and alfalfa seed yields. Oregon State University Agricultural Experiment Station Special Report 862:5-1. Wright, J.L New evapotranspiration crop coefficients. J. Irrig. Drain. Div., ASCE 18:

25 Table 1. Water applied plus precipitation and soil volumetric water content for an alfalfa seed crop submitted to four irrigation treatments. Average soil volumetric water content is the average of the 12- and 2-inch depths. Soil volumetric water content for pre-bloom period in 21 was not available. Malheur Experiment Station, Oregon State University, Ontario, OR. replacement Total water applied Total water applied Average soil volumetric water content from the onset of from dormancy flowering to the last break to the last Clipback to Bloom to last Planned Actual irrigation irrigation bloom irrigation / inch / average average average year average LSD (.5) Treatment NS 7.3 Year NS Trt X Year NS NS NS NS

26 Table 2. Seed quality for alfalfa submitted to four irrigation treatments, Malheur Experiment Station, Oregon State University, Ontario, OR. Germination Germination plus hard seed Abnormal plus dead seed Seed size replacement Avg Avg Avg Average / / / seeds/lb Tango , , ,89 187, ,13 188,68 189,636 19, , , ,13 195, ,9 226,88 26,647 21,212 avg , , , ,299 LSD (.5) Treatment ,416 TrtXYear ,471 Year NS Accord ,21 187,26 184,82 188, ,9 186,2 187, , , ,4 192,28 195, ,97 228,375 28, ,258 avg ,29 199, , ,998 LSD (.5) Treatment ,816 TrtXYear ,599 Year ,8 Average over varieties , , , , ,56 187,35 188,64 19, , , , , ,93 227,231 27, ,648 avg , ,72 193, ,651 LSD (.5) Treatment ,781 TrtXyear ,798 Year ,399

27 Table 3. Seed yield and seed pod dry weight for alfalfa submitted to four irrigation treatments, Malheur Experiment Station, Oregon State University, Ontario, OR. Yield Seed pod yield Biomass yield S eed pod dry weight replacement Average Average Average Average % lb/acre lb/acre tons/acre % Tango , , , ,64.3 1, , , , avg , , LSD (.5) Treatment TrtXYear Year NS 3. Accord , , ,73.4 1, , , , , avg , LSD (.5) Treatment TrtXYear Year Average over varieties Oa 129.la 237.3a 239.7a , a 7.4a 15.2a b 488.7b 34.3b 473.4b 1, , ,452. 1, b 2.lb 26.Obc Ob 411.4b 18.7c 429.7b 1, ,253. 1, c 16.7c 27.lb 22.9b b 112.7c 82.ld 263.2c 1, c 1.ld 21.Oc 19.Oc avg , , , LSD (.5) Treatment TrtXYear Year

28 4 I inch depth S S,.k S S. I. S S. $5. 1 Y= X R2 =.72, P =.1 I inch depth 3 2 S I S S S S S S Si. S S S 1 Y = R2 =.72, P.33X = Volumetric water content - Neutron probe, % Figure 1. Relationship between volumetric soil water content measured by neutron probe and by Gro-Point sensors. Malheur Experiment Station, Oregon State University, Ontario, OR. 18

29 Y = X R2 =.81 P = Y = X -.784X2 =.84, P =.1 S Y X -.41X2 S - R2 =.7, P = Y = X -.59X2 R2=.86,P= replacement 3 year average Figure 2. Alfalfa seed germination response to replacement, averaged over two varieties. Maiheur Experiment Station, Oregon State University, Ontario, OR. 19

30 Y = X -.1 3X 2 6 R2 =.57, P = ci 1 Y X -.73X ( 6 R2 =.68, P S 8 CO I U '. Y = X - O.82X2 R2 =.3, P = NS 6 E ' Y = X -.42X2 6 R2 =.69, P =.1 3 year average replacement Figure 3. Alfalfa seed germination plus hard seed response to replacement, averaged over two varieties. Matheur Experiment Station, Oregon State University, Ontario, OR. 2

31 1 R29.1..' 8 Y X a3 Y = X +.68X 2 2 R2=.2,P=NS E o S 23 3 Y = X +.42X 2 R2 =.69, P = replacement 3 year average Figure 4. Alfalfa abnormal plus dead seed response to replacement, averaged over two varieties. Maiheur Experiment Station, Oregon State University, Ontario, OR. 21

32 U) C U) -c F Y = X R2 =.61, P = U) (I) U) U) ci) N C/) (I) ci) C/) U) C U) = -C I- U) C (T5 = -C Y= X+9.14X2 R2 =.83, P = U) X X2 1 2 b 19 3 year replacement Figure 5. Alfalfa seed size response to replacement, averaged over two varieties. Malheur Experiment Station, Oregon State University, Ontario, OR. 22

33 5 4 (I) 5 o X -.31X R2 =.71, P = o 2 S 1 S S. 21 Y = X +.37X 2 R2 =.9, P =.1 - Ci) Y= X.. S 22 U) 3 2 S S 5 E 1 o o r Ṣ X -.245X2 1 R2 =.93, P =.1 3 year average replacement Figure 6. Alfalfa biomass dry yield response to replacement, averaged over two varieties. Malheur Experiment Station, Oregon State University, Ontario, OR. 23

34 3 S Y X -.38X2 S R2 =.57, P = I 3 Y = X - 22 R2 =.44, P =.1. -o 3 o I 23 ci) 1 y = X - R2=.51, P =.1 ci) Co year average SI 1 Y= X-.84X2 S R2 =.73, P replacement Figure 7. Alfalfa seed pod dry weight response to replacement, averaged over two varieties. Malheur Experiment Station, Oregon State University, Ontario, OR. 24

35 Y = X -.438X2 R2 =.32, P = S Y = X -.587X 2 L. 15 R2=.47,P= S S -a > 2 -o S U ci) ci) 5 Y= X R2 =.53, P =.1 (J) S 1 5 Y = X -.556X2 R2 =.61, P =.1 3 year average replacement Figure 8. Alfalfa seed pod yield response to replacement, averaged over two varieties. Maiheur Experiment Station, Oregon State University, Ontario, OR. 25

36 9 S S Y= X-.221X2 R2 =.58, P = Ct -Q -o -o C') Y = X -.95X 2 R2 =.64, P =.1 S S Y = X -.334X2 R2 =.48, P =.1 S 5 6 S S Y = X -.245X2 -. P 1-3 year average replacement Figure 9. Alfalfa seed yield response to replacement, averaged over two varieties. Maiheur Experiment Station, Oregon State University, Ontario, OR. 26

37 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 441 field corn was planted with a John Deere model 71 Flexi Planter on May 24. Seed spacing was one seed every 7 inches. Plots were sidedressed with 158 lb nitrogen (N), 85 lb phosphorous, 6 lb sulfates, 6 lb zinc, 1 lb boron, 5 lb manganese, and 1 lb elemental sulfur/acre on April 26. Plots were 7.33 by 3 ft and herbicide treatments were arranged in a randomized complete block with four replicates. Herbicide treatments were applied with a CO2-pressurized backpack sprayer. The sprayer was calibrated to deliver 1 gal/acre at 3 psi for the Option trial and 2 gal/acre at 3 psi for the Impact trial. Crop response and weed control were evaluated throughout the growing season. Corn yields were determined by harvesting ears from 26-ft sections of the center 2 rows in each 4-row plot on November 11. The harvested ears were shelled and grain weight and percent moisture content were recorded. Grain yields were adjusted to 12 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 =.5). 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 32 percent urea ammonium nitrate (UAN) following 27

38 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. 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 1). 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.88 or.131 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 2). 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 3). 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 28 (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 28 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. 28

39 Tab'e 1. Weed control with Option herbicide applied with different surfactants and with Distinct in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. L Pigweed C. lambsquarters Weed H. night- Barnyardshade Kochia grass Treatment Rate* Timingt lb al/acre pt/acre % v/v Untreated Option + MSO + 32% N MP 99 a 96 ab 1 1 a 1 a Option + MSO + 32% N MP 99 a 99 ab 1 1 a 1 a Option + COC + 32% N % + 3. MP 1 a 84 c 1 99 a 98 ab Option + MSO + AMS lb MP 99 a 97 ab 1 1 a 98 a Option + 32% N MP 96 b 72 d 1 86 b 89 b Option + Distinct + MSO MP 1 a 1 a 1 1 a 99 a + UAN 32% + 3. Option + Distinct+ MSO MP 1 a 1 a 1 1 a 1 a + UAN 32% + 3. *Herbicide rates are in lb al/acre. Additive rates are in pt/acre, percent v/v, or lb/acre. ttreatments were applied mid-postemergence (MP) to corn at the V4 growth stage on June 2. control was evaluated July 18. 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 =.5 confidence level. species were a mixture of Powell amaranth and redroot pigweed. 29

40 Table 2. Injury, height, and yield with Option herbicide applied with different additives in field corn, Experiment Station, Oregon State University, Ontario, OR, 25. Field corn Height Treatment Rate* Timingt Yields lb al/acre / in bu/acre pt/acre % v/v Untreated Option + MSO + 32% N MP Option + MSO + 32% N MP Option + COC + 32% N % + 3. MP Option + MSO + AMS lb MP Option + 32% N MP Option + Distinct + MSO MP UAN 32% + 3. Option + Distinct + MSO MP UAN 32% + 3. LSD (.5) NS NS *Herbicide rates are in lb ai/acre. Additive rates are in pt/acre, percent v/v, or lb/acre. ttreatments were applied mid-postemergence (MP) to corn at the V4 growth stage on June 2. untreated control was not included in the ANOVA for percent injury. SCorn was harvested November 11 and yields were adjusted to 12 percent moisture content. 3

41 Table 3. Weed control with Impact herbicide in combinations with other herbicides applied in field corn, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. L Weed Untreated Kochia Treatment Rate* Tlmlngt Pigweed C. lambsquartershade H. night- lb al/acre / % v/v Barnyardgrass Dual II Magnum 1.43 PRE Dual II Magnumfb 1.43 PRE Impact + AAtrex + MSO % MP +32%N Dual II Magnumfb 1.43 PRE Callisto + AAtrex + COC MP +32%N 1.%+2.5% Dual II Magnumfb 1.43 PRE Clarity + NIS + 32% N % + MP 2.5% Dual II Magnumfb 1.43 PRE Option + MSO + 32% N % + MP 2.5% Outlookfb.75 PRE Impact +AAtrex+ MSO % MP +32%N +2.5% LSD (.5) NS *Herbiclde rates are in lb al/acre. Additive rates are in percent v/v. tapplication timings were preemergence (PRE) on May 26 and mid-posternergence (MP) applied to corn at the V4 9rowth stage on June 18. contro' was evaluated July 18. The untreated control was not included in the ANOVA for weed control. species were a mixture of Powell amaranth and redroot pigweed. 31

42 Table 4. Injury, height, and yield with Impact herbicide applied in field corn, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Treatment Rate* Timingt lb ai/acre % v/v Field corn Height Yields / in bu/acre Untreated Dual Il Magnum 1.43 PRE Dual H Magnumfb Impact + AAtrex MSO + 32%N % + 2.5% PRE MP Dual Il Magnumfb Callisto + AAtrex + COC +32%N % +2.5% PRE MP Dual II Magnumfb Clarity + NIS + 32% N % + 2.5% PRE MP Dual II Magnumfb Option + MSO + 32% N % + 2.5% PRE MP Outlookfb Impact + AAtrex + MSO + 32% N % + 2.5% PRE MP LSD (.5) NS NS *Herbicide rates are in lb ai/acre. Additive rates are in perce nt v/v. tapplication timings were preemergence (PRE) on May 26 and mid-postemergence (MP) applied to corn at the V4 9rowth stage on June 18. 4The untreated control was not included in the ANOVA for percent injury. SCorn was harvested November 11 and yields were adjusted to 12 percent moisture content. 32

43 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. ChateauR, 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 9) at.25 percent v/v. Fall applications were made December 13, 24 and spring applications were made February 23, 25. Herbicide treatments were arranged in a randomized block design with four replicates. Plots were loft wide by 3 ft long. Herbicides were applied with a CO2-pressurized backpack sprayer calibrated to deliver 2 gal/acre at 3 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 1). 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 33

44 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. Table 1. Weed densities in response to fall and spring herbicide applications to dormant peppermint in Nampa, ID, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Treatmerlt* Ratet lb al/acre Weed Prickly Blue mustard Downy brome lettuce Kochia Pigweed Fall Spring Fall Spring no13 Untreated control Siribar + Karmex + Stinger + Prowl + NIS % Sinbar + Karmex + Stinger + Chateau + NIS Sinbar + Karmex + Chateau + Gramoxone Extra + NIS Chateau + Treflan + Stinger +NIS Chateau + Siribar + Stinger +NIS Chateau + Karmex + Stinger +NIS Chateau + Treflan + Gramoxone Extra + NIS Chateau + Sinbar + Gramoxone Extra + NIS Chateau + Karmex + Gramoxone Extra + NIS Chateau + Gramoxone Extra +NIS % % % % % % % % % LSD (.5) Chateau + Stinger % Chateau + Stinger % *Fall applications were made December 13, 24. Spring treatments were made February 23, 25. therbicide rates are lb ai/acre. NIS (nonionic surfactant, Activator 9) was applied at.25 percent v/v. mustard and downy brome densities were counted on April 28, 25. 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. treatments of Chateau plus Stinger were applied in the fall and again in the spring and are not included in the statistical analyses. 34

45 IDENTIFICATION OF HERBICIDES FOR USE IN NATIVE FORB SEED PRODUCTION Clinton C. Shock, Joey lshida, and Corey Ransom Maiheur 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, 1/2, 1, 2, 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 lii, 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. 35

46 Materials and Methods Two initial screening trials were initiated in 25 at the Maiheur 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-I at the Malheur Experiment Station and was used to fill 224 half trays (.28 m by.28 m). On October 13 and 14, seven native species were planted in 32 half trays at 5 seeds per tray with planting depth dependent upon the species (Table I). Seeds were equally spaced at 5 by 5 locations with 2 seeds per location. Table 1. Forb species planted in the greenhouse herbicide screening trial at the Malheur Experiment Station, Ontario, OR, 25. Species Common name Depth, mm, (inches) Eriogonum umbellatum Sulfur buckwheat 3, (1/8) Penstemon acuminatus Sand penstemon 3, (1/8) Penstemon deustus Hotrock penstemon 3, (1/8) Penstemon speciosus Royal or Sagebrush penstemon 3, (1/8) Lomatium dissectum Fern leaf biscuitroot 12, (1/2) Lomatium triternatum Nineleaf desert parsley 12, (½) Lomatium grayi Gray's lomatium 12, (½) The trays were saturated October 17 and drained. The next day the trays were moved into a cooler set at I C (34 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 15 all trays were moved to the greenhouse head house for spraying. Four replicate trays of each of species received eight herbicide treatments (Table 2). Products were applied in a spray chamber at 19.2 gal/acre of water with an 82E nozzle at 3 psi moving at 2 mph. The air temperature was 53 F with 5 percent relative humidity. On November16 each tray received 1/8 inch of water to incorporate the herbicide and the trays were returned to the cooler at 34 F. On November 21 Lomatium triternatum, L. grayi, and Eriogonum umbellatum were moved to the greenhouse. On November 28, supplemental light was added to the greenhouse for 1 hours per day. On December 12 the other forbs were moved to the greenhouse. Forbs were irrigated as needed and plant stands were counted twice a week. Field Herbicide Screening Trial The field was prepared in October 25 and bedded into 76-cm (3-inch) rows. On October 23, drip tape (T-Tape TSX )was buried at.3-rn (1-ft) depth and spaced 1.52 m (5 ft) apart. Two rows of forbs were planted.38 m (15 inches) to each side of the drip tape. Each species (Table 1) was planted in a single row for a length of 36

47 over 122 m (4 ft). The drip tape was buried on alternating inter-row spaces. The flow rate for the drip tape was.34 gal/mm/i ft at 8 PSI with emitters spaced.4 m (16 inches) apart, resulting in a water application rate of.66 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, 26. 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 2, perpendicular to the direction of the plant rows, with four replicates. A spray boom with three 82 E nozzles 2 inches apart covered the 5-ft plot width. Applications were based on 2 gal/acre, 3 psi, at 2.63 mph. The conditions were air temperature of 42 F, soil surface temperature 43 F, 1 percent cloud cover, and wind at 2 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 1.1 lb ai/acre on January 6. Table 2. Herbicides screened for forb tolerance at the Malheur Experiment Station, Ontario. OR, Treatment Product rate Rate Plant stands, % Lomatium Eriogonum Lomatium lb a i/acre grayi umbellatum dissectum Dec12 Jan1 Dec3 Check none none Prefar4.OEC 5qt/acre Kerb 5 WP 2 lb/acre TreflanHFP.75 pt/acre 3/ Prowl 3.8 SC 1.58 pt/acre 3/ Balan 6 DF 2 lb/acre Outlook 6. EC 14 fi oz/acre 2/ Lorox 5 DF 1 lb/acre LSD (.5) 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 2). L. triternatum emerged slowly. In this preliminary screening trial, the forb species are tolerating different herbicides (Fig. 1). 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. 37

48 LOGR* _.._ ERUM*** 5 4 C U) 4-, (I) 4-, C U) Check Prefar Kerb Treflan Prowl Balan Outlook Lorox Product Figure 1. Plant stand of three forb species treated with seven herbicides, Maiheur Experiment Station, Oregon State University, Ontario, OR. LOGR is Lomatium gray!, ERUM is Eriogonum umbellatum, and LODI is Lomatium dissectum. * Treatment differences are significant at P =.5, Treatment differences are significant at P =.1. 38

49 SUBSURFACE DRIP IRRIGATION FOR NAT WE FORB SEED PRODUCTION Clinton C. Shock, Erik B.G. Feibert, and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Introduction Native forb seed is needed to restore rangelands of the Intermountain West. Commercial seed production is necessary to provide the quantity of seed needed for restoration efforts. A major limitation to economically viable commercial production of native forb seed is stable and consistent seed productivity over years. Variations in spring rainfall and soil moisture result in highly unpredictable water stress at seed set and development. Excessive water stress during seed set and development is known to compromise yield and quality of other seed crops. Native forbs are not competitive with crop weeds. Both sprinkler and furrow irrigation promote seed production, but risk the encouragement of weeds. Furthermore, sprinkler and furrow irrigation can lead to the loss of plant stand and seed production to fungal pathogens. This project tests buried drip tapes for timely irrigation to supply only limited amounts of water. By burying drip tapes at 3-cm (1-ft) depth, and avoiding wetting of the soil surface, we hope to assure flowering and seed set without encouraging weeds or opportunistic diseases. Materials and Methods Seed of the seven forb species (Table 1) was received in late November 24 from the Rocky Mountain Research Station (Boise, ID). The plan was to plant the seed in the fall of 24, but due to excessive rainfall in October, the completion of ground preparation and planting was postponed to 25. To ensure germination in the spring of 25, the seed was submitted to a cold stratification treatment. The seed was soaked overnight in distilled water on January 26, 24. After soaking, the water was drained and the seed soaked for 2 minutes in a 1 percent by volume solution of 13 percent bleach in distilled water. The water was drained and the seed placed in a thin layer in plastic containers. The plastic containers had lids with holes drilled to allow air movement. The seed containers were placed in a cooler set at approximately 34 F. Every few days the seed was stirred and, if necessary, distilled water added to maintain moisture. In late February, seed of Lomatium grayi and L. triternatum had started sprouting. The field was bedded into 76-cm (3-inch) rows. In late February 25, drip tape (T-Tape TSX ) was buried at 3-cm (1 -ft) depth and spaced I.52 m (5 ft) apart. The drip tape was buried on alternating inter-row spaces. The flow rate for the drip tape was.34 gal/min/1 ft at 8 PSI with emitters spaced 41 cm (16 inches) apart, 39

50 resulting in a water application rate of.66 inch/hour. Water was filtered through sand media filters and application duration was controlled automatically. Water applied was measured. On March 3, seed of all species (Table 1) was planted in 76-cm (3-inch) rows using a custom-made plot grain drill with disk openers. Two rows of forbs were planted 38 cm (15 inches) to each side of the drip tape. All seed was planted at 2-3 seeds/ft of row. The Eriogonum umbellatum and Penstemon spp. were planted at.64-cm (.25 inch) depth and the Lomatium spp. at.5 inch depth. The trial was irrigated with a minisprinkler system (RIO Turbo Rotator, Nelson Irrigation Corp., Walla Walla, WA) for even stand establishment from March 4 to April 29. The trial was irrigated on March 4 (5 hours), March 8 (3 hours), March 11 (2 hours), March 14 (2 hours), April 12 (4 hours), April 15 (3 hours), April 26 (4 hours), and April 29 (3 hours). Risers were spaced 7.6 m (25 ft) apart along the flexible polyethylene hose laterals that were spaced 9 m (3 ft) apart and the water application rate was.1 inch/hour. The drip irrigation system was used in June and July. Results and Discussion Eriogonum umbeliatum, Lomatium triternatum, and L. grayi started emerging on March 29. All other species except L. dissectum emerged by late April. Very few L. dissectum ever emerged. Heavy weed populations emerged with the sprinkler irrigation and spring rains. Weeds were controlled by cultivation and hand weeding. Appropriate herbicides for weed control are urgently needed to reduce production costs. A total of 4.4 cm (1.72 inches) of water was applied with the minisprinkler system. Starting June 24, the field was irrigated using the drip system. A total of 9.5 cm (3.73 inches) of water was applied with the drip system from June 24 to July 7. Thereafter the field was not irrigated. Preliminary results indicate that relatively little irrigation water will be needed to sustain native forbs. Plant stands for Eriogonum umbellatum, Penstemon acuminatus, P. deustus, Lomatium triternatum, and L. gray! were acceptable but not perfect. In early October 25, more seed was received from the Rocky Mountain Research Station for replanting. The E. umbellatum and Penstemon spp. plots had the blank lengths of row replanted by hand. The Lomatium spp. plots had the entire row lengths replanted using the planter. The seed was replanted on October 26, 25 for germination in the spring of 26. Forbs established in 25 will receive three irrigation treatments: mm/yr; low (up to 1 cm/yr, 4 inches/yr); or modest (up to 2 cm/yr, 8 inches/yr) supplemental irrigation in 26. Water will be applied so that the soil surface is not appreciably moistened. Water will be applied in small increments during flowering and seed formation. Four replicates of each forb and each irrigation rate will be established. The first 4

51 measurements of seed yield will occur in 26. This research effort is expected to require at least two seed harvest years. The current work is funded through 26. Table 1. Forb species p1anted in the irrigation trial at the Malheur Experiment Station, Ontario, OR, 25. Species Common name Origin Collection Year Eriogonum umbeilatum Sulfur buckwheat Shoofly Road 24 Penstemon acuminatus Sand penstemon Bliss Dam 24 Penstemon deustus Hotrock penstemon Black Cr. Rd. 23 Penstemon speciosus Sagebrush penstemon Leslie Gulch 23 Lomatium dissectum Fernleaf biscuitroot Mann Creek 23 Lomatium triternatum Nineleaf desert parsley Hwy Lomatium grayi Gray's lomatium Weiser R. Road 24 Technology Transfer The concept of producing native forb seed as a crop and the initial planting described above was presented to growers and fieldmen at the Malheur Experiment Station Field Day, July 13,

52 25 ONION VARIETY TRIALS Clinton C. Shock, Erik B. C. Feibert, and Lamont D. Saunders Malheur Experiment Station Oregon State University, Ontario, OR Lynn Jensen Malheur County Extension Service Oregon State University, Ontario, OR Krishna Mohan University of Idaho, Parma, ID Introduction The objective of the onion variety trials was to evaluate yellow, white, and red onion varieties for bulb yield, quality, and single centers. Five early season yellow varieties were planted in March and were harvested and graded at the end of August. Thirty-five full season varieties (27 yellow, 4 red, and 4 white) were planted in March, harvested in September 25, and evaluated in January 26. Materials and Methods The onions were grown on a Greenleaf silt loam previously planted to wheat. In the fall of 24, the wheat stubble was shredded and the field was irrigated and disked. Soil analysis indicated the need for 2 lb sulfur/acre and 1 lb boron/acre, which were broadcast in the fall of 24 after disking. In early March 25 the field was moldboard-plowed, groundhogged, roller-harrowed, and bedded. A full season trial and an early maturing trial were conducted adjacent to each other. Both trials were planted on March 15 in plots 4 double rows wide and 27 ft long. The early maturing trial had 5 varieties from 2 seed companies (Table 1) and the full season trial had 35 varieties from 8 seed companies (Table 3). The experimental design for each trial was a randomized complete block with five replicates. A sixth nonrandomized replicate was planted for demonstrating onion variety performance to growers and seed company representatives. Seed was planted in double rows spaced 3 inches apart at 9 seeds/ft of single row. Each double row was planted on beds spaced 22 inches apart with a customized planter using John Deere Flexi Planter units equipped with disk openers. The onion rows received 3.7 oz of Lorsban 1 5G per 1, ft of row (.82 lb ai/acre), and the soil surface was rolled on March 2. The field was irrigated on March 18. Onion emergence started on April 11. On May 4, alleys 4 ft wide were cut between plots, leaving plots 23 ft long. From May 24 through 28, the seedlings were hand thinned to a 42

53 plant population of two plants/ft of single row (6-inch spacing between individual onion plants, or 95, plants/acre). The field was sidedressed with 1 lb of nitrogen (N)/acre as urea and cultivated on June 8. On July II, the field was sidedressed with 1 lb N/acre as urea. The onions were managed to avoid yield reductions from weeds, pests, and diseases. These factors were not all avoided in 25. Due to high rainfall in April and May, Bravo at 2.25 lb ai/acre was applied on May 2 for preventive fungal disease control. Weeds were controlled with an application of Prowl at.83 lb ai/acre, Goal at.13 lb ai/acre, Buctril at.19 lb ai/acre, and Poast at.21 lb al/acre on June 4. After lay-by the field was hand weeded as necessary. Thrips were controlled with aerial applications of the following insecticides: June 16, Warrior plus Lannate ; June 24, Warrior; July 1, Warrior plus Lannate; July 18, Warrior plus Lannate; July 26, Warrior plus MSR ; August 3, Warrior plus Lannate; August 1, Warrior plus MSR; August 14, Warrior plus Lannate; August 2, Warrior plus MSR. Warrior was applied at.3 lb al/acre, Lannate at.45 lb ai/acre, and MSR at.5 lb al/acre. The trial was furrow irrigated when the soil water potential at 8-inch depth reached -25 kpa. Soil water potential was monitored by six granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 2SS, Irrometer Co. Inc., Riverside, CA) installed in mid-june below the onion row at 8-inch depth. The sensors were automatically read three times a day with an AM-4 meter (Mike Hansen Co., East Wenatchee, WA). The last irrigation was on August 3. Onions in each plot were evaluated subjectively for maturity by visually rating the percentage of onions with the tops down and the percent dryness of the foliage. The percent maturity was calculated as the average percentage of onions with tops down and the percent dryness. The early maturing trial was evaluated for maturity on August 22 and the full season trial on August 3 and September 9. The number of bolted onion plants in each plot was counted. Onions in each plot were evaluated subjectively for damage from iris yellow spot virus on August 19. Each plot was rated according to the number of leaves with symptoms per plant: = no symptoms, 5 = at least 3 leaves with symptoms per plant. Onions from the middle two rows in each plot in the early maturity trial were lifted on August 29, and topped by hand and bagged on August 31. On September 1 the onions were graded. The onions in the full season trial were lifted on September 12 to field cure. Onions from the middle two rows in each plot of the full season trial were topped by hand and bagged on September 2. The bags were put in storage on September 22. The storage shed was managed to maintain an air temperature as close to 34 F as possible. Onions from the full season trial were graded out of storage on January 5, 26. During grading, bulbs were separated according to quality: bulbs without blemishes (No. I s), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botiytis al/li in the neck 43

54 or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger). The No. I bulbs were graded according to diameter: small (<2.25 inches), medium ( inches), jumbo (3-4 inches), colossal ( inches), and supercolossal (>4.25 inches). Bulb counts per 5 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. The red varieties were evaluated subjectively during grading for exterior thrips damage during storage. The bulbs from each red variety plot were rated on a scale from (no damage) to 1 (most damage) for the damage that was apparent on the bulb surface, without removing the outer scales. After grading of the early maturing trial, 1 randomly chosen bulbs from each plot were shipped via UPS ground to Vidalia Labs International in Collins, Georgia. The bulb samples were analyzed for pyruvic acid content on September 2. Bulb pyruvic acid content is a measure of pungency with the unit being micro mols pyruvic acid per gram of fresh weight (pmols/g FW). Onion bulbs having a pyruvate concentration of 5.5 or less are considered sweet according to Vidalia Labs sweet onion certification specifications. In early September bulbs from one of the border rows in each plot of both trials were rated for single centers. Twenty-five consecutive onions ranging in diameter from 3.5 to 4.25 inches were rated. The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured. These multiple-centered onions were ranked according to the diameter of the first single ring: "small double" had diameters less than 1.5 inches, "intermediate double" had diameters from 1.5 to 2.25 inches, and "blowout" had diameters greater than 2.25 inches. Single-centered onions were classed as a "bullet". Onions were considered functionally single centered for processing if they were a "bullet" or "small double." Varietal differences were compared using ANOVA and least significant differences at the 5 percent probability level, LSD (.5). Sixteen full season varieties were in the variety trial in 23, 24, and 25. The data for these varieties were compared over the 3 years. Results and Discussion Varieties are listed by company in alphabetical order. The LSD (.5) values at the bottom of each table should be considered when comparisons are made between varieties for significant differences in performance characteristics. Differences between varieties equal to or greater than the LSD value for a characteristic should exist before any variety is considered different from any other variety in that characteristic. A few experimental varieties were named in 25. 'XP5646' was named 'Orizaba', 'XP5813' was named 'Affirmed', and 'EX5843' was named 'Monarchos'. 44

55 The 25 season was unfavorable for the variety trial. Excessive rain in October of 24 prevented fall fumigation and bedding. Bedding was done in the spring of 25. Planting occurred on the target date of mid-march, but emergence was delayed for reasons unknown. Onion emergence in the variety trial in 25 took 27 days, the longest since 1998 and substantially longer than the average of 19 days for the onion variety trial. Emergence between varieties was uneven. Excessive rain in May delayed cultivation and hand-thinning operations. Thinning is normally done in the first half of May. In 25, thinning was delayed until late May. The high rainfall along with delayed cultivation and thinning resulted in high weed pressure until late May. April, May, and June had fewer growing degree days (5 to 86 F) than average. By the end of June there were 15 percent fewer accumulated growing degree days than the 19-year average. The growing degree days in July and August were close to average. The unfavorable growing conditions prior to bulbing resulted in smaller onion plants at the start of bulbing. The smaller onion plants may have been more susceptible to and more affected by thrips damage. Thrips pressure and iris yellow spot virus pressure were greater than normal during the season. Early Maturity Trial, Five Yellow Varieties The percentage of "bullet" single centers averaged 17.6 percent and ranged from 4 percent for 'Sequoia' to 52.8 percent for 'Montero' (Table 1). The percentage of onions that were functionally single centered averaged 5.4 percent and ranged from 27.2 percent for 'Renegade' to 88.8 percent for Montero. Montero had the highest percentage of bullet and functionally single-centered bulbs in this trial. Total yield averaged 489 cwt/acre and ranged from cwtlacre for 'Denali' to 59.9 cwt/acre for 'XON-14' (Table 2). XON-14, Renegade, and Montero were among the highest in total yield. Colossal-size onion yield averaged 19.5 cwtlacre and ranged from I cwt/acre for Sequoia to 52 cwt/acre for XON-14. XON-14 had the highest yield of colossal bulbs. Maturity on August22 ranged from 16 percent for Montero to 7 percent for Denali. Pyruvate concentration ranged from 4.28 pmols/g FW for Denali to 6.8 pmols/g FW for Montero. Denali had bulb pyruvate concentration low enough (<5.5) to be classified as a sweet onion. Full Season Trial, 27 Yellow Varieties The percentage of "bullet" single centers averaged 49.1 percent and ranged from 4 percent for 'Calibra' to 88 percent for '611' (Table 3). The percentage of onions that were functionally single centered averaged 78.4 percent and ranged from 34.4 percent for 'T-433' and Calibra to 96.1 percent for EX5843. Maturity on September 9 averaged 47.6 percent and ranged from 17 percent for 'SR78ON' to 72 percent for 'Talon'. SR78ON and 'Charismatic' were among the least mature varieties on September 9. 45

56 Marketable yield out of storage in January 25 ranged from cwt/acre for 'King George' to 794 cwtlacre for 'Sweet Perfection' (Table 4). Sweet Perfection and SR78ON were among the varieties with the highest marketable yield. Supercolossal-size onion yield ranged from cwtlacre for many varieties to 21 cwtlacre for Charismatic. Charismatic, Sweet Perfection, and SR78ON were among the varieties with the highest supercolossal yield. Not counting supercolossals, colossal-size onion yield ranged from cwt/acre for Talon, King George, and 'SX72N' to cwt/acre for SR78ON. SR78ON and Charismatic were among the highest in colossal bulb yields. Jumbo-size onion yield averaged 332 cwt/acre and ranged from cwt/acre for Talon to cwtlacre for Sweet Perfection. Decomposition in storage ranged from.3 percent for '414' to 6.1 percent for 'Harmony'. No. 2 bulbs ranged from cwt/acre for many varieties to 5.2 cwtlacre for King George. Full Season Trial, Four Red Varieties The percentage of "bullet" single centers ranged from 4 percent for 'Red Fortress' to 92.8 percent for 'T-817' (Table 3). The percentage of functionally single-centered onions ranged from 64.8 percent for 'Salsa' to 98.4 percent for T Total marketable yield ranged from 73.2 cwt/acre for T-817 to cwt/acre for Salsa (Table 4). Jumbo-size onion yield ranged from.9 cwtlacre for to 11.7 cwtlacre for Salsa. Decomposition in storage ranged from.7 percent for T-81 7 and 'Red Bull' to 3 percent for Red Fortress. No. 2 bulbs ranged from cwtlacre for T-81 7, Red Bull, and Salsa to 2.4 cwtlacre for Red Fortress. Red onion yield was apparently seriously hurt by thrips pressure and iris yellow spot virus. Subjective evaluation of thrips damage to red onions in storage was low for all varieties. averaging.1 from a rating of to 1, with no difference among varieties. Full Season Trial, Four White Varieties The percentage of "bullet" single centers ranged from 24 percent for XP5646 to 3.4 percent for 'Brite Knight' (Table 3). The percentage of functionally single-centered onions ranged from 62.4 percent for B rite Knight to 71.2 percent for 'Gladstone'. Total marketable yield ranged from cwt/acre for Gladstone to cwtlacre for XP5646 (Table 4). Colossal-size onion yield ranged from 1.1 cwtlacre for Gladstone to 2.1 cwt/acre for XP5646. Decomposition in storage ranged from 21 percent for Gladstone to 7.3 percent for 'EX71 6'. No. 2 bulbs ranged from cwtlacre for XP5646 and EX716 to 6.2 cwt/acre for Brite Knight. Iris Yellow Spot Virus Rating Subjective rating of damage from iris yellow spot virus for the full season varieties, on a scale from to 5, ranged from.7 for SR78ON to 2.4 for Red Bull (Table 3). 46

57 23-25 Data - Full Season Varieties Onion yields were highest in 23 and lowest in 25 (Table 5). The percentage of functionally single-centered onions was lowest in 23 and highest in 25. Averaged over the 3 years, Sweet Perfection, Ranchero, T-433, and Harmony were among the varieties with the highest total yield (Table 5). Averaged over the 3 years, Ranchero and Sweet Perfection were among the varieties with the highest marketable yield. Averaged over the 3 years, 'Maverick' had the highest supercolossal onion yield. Averaged over the 3 years, 611 and SR74ON were among the varieties with the highest percentage of bullet single centered bulbs. Averaged over the 3 years, 611, SR74ON, Sabroso, and Montero were among the varieties with the highest percentage of functionally single-centered bulbs 47

58 Table 1. Onion multiple-center rating for early maturing varieties, Malheur Experiment Station, Oregon State University, Ontario, R, 25. Multiple center Seed Bulb Intermediate Small Functionally single centered company Variety color Blowout double double Bullet "bullet + small double" / Sakata XON-14 Y Nunhems Denali Montero Renegade Sequoia Y Y Y Y Average LSD (.5) NS Table 2. Performance data for early maturing onion varieties harvested on August 31 and graded on September 1, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Ma rketable yield by grade Non-marketable yield Maturity Seed Bulb Total Total No. on Aug. Pyruvate company Variety color yield Total 4-4% in 3-4 in in rot 2s Small 22 concentration cwtlacre % -- cwt/acre -- % pmols/g FW Sakata XON-14 Y Nunhems Denali Y Montero Y Renegade Y Sequoia Y Average LSD (.5) NS NS NS NS

59 Table 3. Onion multiple-center rating and iris yellow spot virus rating for long season varieties, Malheur Experiment Station, Oreqon State University, Ontario, OR, 25. Seed company Variety Bulb color Blowout Multiple centered Intermediate double Small double / Bullet Bullet + small double* A. Takil T-433 Y T-817 R Iris yellow spot virus ratingt Bejo Calibra Crocket Sedona Talon Y Y Y Y Gladstone W Red Bull R Crookham Harmony Y Sweet Perfection Y Rispens King George Y Brite Knight W Red Fortress R Sakata XON-55Y Y Seedworks Seminis Maverick Varsity Charismatic XP5813 XP5819 EX5843 XP5646 EX716 Y Y Y Y Y Y Y Y Y W W Nunhems Granero Y Montero Pandero Ranchero Sabroso Vaquero SX74ON SR78ON SX72N Salsa Y Y Y Y Y Y Y Y R Average LSD (.5) *Functionally single centered. tsubjectjve rating: = no damage, 5 = total damage

60 Table performance data for experimental and commercial onion varieties graded out of storage in January 26, Malheur Experiment Station, Oreqon State University, Ontario, OR. Marketable yield by grade Bulb Non-marketable yield Maturity Seed Bulb Total counts Total Neck Plate Black No. Aug. Sept. Thrips company Variety color yield >4% in damage* Total >4% in 4-4% in 3-4 in 21h-3 in rot rot rot mold 2s Small 3 9 cwt/acre #/5 lb --- % of total yield cwt/acre A.Takii T-433 Y T-817 R Bejo calibra Y Crocket Y Sedona Y Talon Y Gladstone W Red Bull R Crookham Harmony Y Sweet Perfection Y Rispens King George Y Brite Knight W Red Fortress R Sakata XON-55Y Y Seedworks Maverick Y Varsity Y Y Y Y

61 Table performance data for experimental and commercial onion varieties graded out of storage in January 26, Malheur Experiment Station, Oregon State University, Ontario, OR. Seed Bulb company Variety color Marketable yield by grade Total yield Total >41/4 in 4..41% in 3-4 in in cwtlacre Bulb counts >41/4 in #/5 lb Total rot Non-marketable yield Maturity Neck Plate Black No. Aug. Sept. rot rot mold 2s Small 3 9 % of total yield cwt/acre -- Thrips damage* Seminis Chansmatic Y XP5813 Y XP5819 ' EX5843 Y XP5646 W EX716 W Nunhems Granero Y Montero Y Pandero Y , Ranchero Y Sabroso Y Vaquero Y SX74ON Y R78N Y SX72N Y Salsa R Average LSD ,3 NS NS * Thrips damage: = least damage, 1 = most damage.

62 Table 5. Yield and single center rating for onion varieties in Malheur Experiment Station, Oreqon State University, Ontario, OR, 25. Marketable yield Single centeredness Seed Bullet + small company Variety Total yield Total >4% in 4-4% in Bullet double* cwt!acre / 23 - A. Takii T-433 1, Bejo Gladstone Crookham Harmony 1, , Sweet Perfection 1,186. 1, Rispens Red Fortress Seedworks Maverick (61) 1, , Varsity Nunhems *Functionally single centered , , Granero Montero(72N) 1, ,51.8 1, Pandero Ranchero Sabroso Vaquero SR74 ON 1, , , , ,7.7 1, ,52. 1, Average 1, A. Takii T Bejo Gladstone Crookham Harmony 1, Sweet Perfection 1, Rispens Red Fortress Seedworks Maverick (61) Varsity Nunhems Average 611 Granero Montero (72N) Pandero Ranchero Sabroso Vaquero SR74 ON , ,

63 Table 5. Yield and single center rating for onion varieties in Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Marketable yield Single centeredness Seed Total Bullet + small company Variety yield Total >4¼ in in Bullet double* cwt/acre / 25 A. Takii T Bejo Gladstone Crookham Harmony Sweet Perfection Rispens Red Fortress Seedworks - Maverick (61) Varsity Nunhems Average A. Takii 611 Granero Montero (72N) Pandero Ranchero Sabroso Vaquero SR74 ON year average T Bejo Gladstone Crookham - - Harmony Sweet Perfection 1,43.8 Rispens Red Fortress 51.9 Seedworks Maverick (61) Varsity Nunhems Granero Montero (72N) 82.3 Pandero Ranchero 1,21.5 Sabroso Vaquero SR74ON Average J LSD(.5)Year LSD (.5) Variety LSD(.5)Var.Xyear *Functionally single centered

64 EVALUATION OF OVER-WINTERING ONION FOR PRODUCTION IN THE TREASURE VALLEY - 24/25 TRIAL Clinton C. Shock, Erik B. C. Feibert, and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Introduction The objective of the trial was to evaluate onion varieties for over wintering onion production in the Treasure Valley of eastern Oregon and western Idaho. Bulb yield, grade, single centeredness, and pungency were evaluated. Eight varieties were planted in August 24. They were harvested and graded in June 25. Marketable yield ranged from 393 to 762 cwtlacre. Five of the varieties were considered sweet due to their pyruvate content. Materials and Methods The onions were grown on a field of Owyhee silt loam located northeast of the Malheur Experiment Station on Railroad Ave. between Highway 21 and Alameda Drive. Seed of the 8 varieties (Table 1) was planted in double rows spaced 3 inches apart at 9 seeds/ft of single row on August 3, 24. Each double row was planted on beds spaced 2 inches apart with a customized planter using John Deere Flexi Planter units equipped with disc openers. On October 26 the seedlings were hand thinned to a plant population of 95, plants/acre (6.6-inch spacing between individuat onion plants). All cultural practices were performed by the grower. Onions in each plot were evaluated subjectively for maturity on June 24, 25 by visually rating the percentage of onions with the tops down and the percent dryness of the foliage. The percent maturity was calculated as the average of the percentage of onion with tops down and the percent dryness. Onions from the middle two rows in each plot were lifted, topped by hand and bagged on June 28, 25. The onion bags were transported to the Malheur Experiment Station and graded. Before grading, all bulbs from each plot were counted to determine actual plant populations at harvest. During grading, bulbs were separated according to quality: bulbs without blemishes (No. is), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis al/li in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger). The No. i bulbs were graded according to diameter: small (<21/4 inch), medium inch), jumbo (3-4 inch), colossal (4.4% inch), and supercolossal (>41,4 inch). Bulb counts per 5 lb of supercolossal onions 54

65 were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. On June 28, 1 randomly chosen bulbs from each plot were shipped via UPS ground to Vidalia Labs International in Collins, Georgia. The bulb samples were analyzed for pyruvic acid content on July 8. Bulb pyruvic acid content is a measure of pungency with the unit being micro mols pyruvic acid per gram of fresh weight (pmols/g FW). Onion bulbs having a pyruvate concentration of 5.5 or less pmols/g FW are considered sweet according to Vidalia Labs sweet onion certification specifications. After harvest bulbs from each plot were rated for single centers. Twenty-five onions ranging in diameter from 3.5 to 4.25 inches were rated. The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured. These multiple-centered onions were ranked according to the interior diameter of the first single ring: "small double" had interior diameters less than 1 1/2 inches, "intermediate double" had diameters of 1Y2-2% inches, and "blowout" had diameters over 2% inches. Single-centered onions were classed as a "bullet". Onions were considered functionally single centered for processing if they were a "bullet" or "small double." Varietal differences were compared using ANOVA and least significant differences at the 5 percent probability level, LSD (.5). Results and Discussion Varieties are listed by company in alphabetical order. The LSD (.5) values at the bottom of each table should be considered when comparisons are made between varieties for significant differences in performance characteristics. Differences between varieties equal to or greater than the LSD value for a characteristic should exist before any variety is considered different from any other variety in that characteristic. Grower practices were adequate to control thrips during seedling emergence and early plant growth, critical phases for successful over-wintering onion production in the Treasure Valley. The winter of in the Treasure Valley was mild with the lowest temperature of 12 F occurring on January 4, 25. Plant populations were below the target of 95, plants per acre for some varieties. Plant populations ranged from 79,23 plants per acre for 'XON-43Y' to 96,589 plants per acre for 'Hi Keeper' (Table 1). Total yield averaged 63 cwtlacre and ranged from 424 cwtlacre for 'McBee' to 87 cwt/acre for 'Stansa' (Table 1). Stansa and Hi Keeper had the highest total yield. Marketable yield averaged 594 cwt/acre and ranged from 393 cwt/acre for McBee to 762 cwt/acre for Hi Keeper. Supercolossal-size bulb yield averaged 9.8 cwflacre and ranged from cwt/acre for McBee, XON-43Y, and 'Toughball' to 45.1 cwtlacre for Stansa. Stansa had the highest yield of super colossal bulbs. Not considering supercolossals, colossal-size onion yield averaged 77.4 cwt/acre and ranged from 2.4 cwtlacre for McBee to cwt/acre for Stansa. Stansa had the highest colossal bulb yields. 55

66 Maturity on June 24 ranged from 26 percent for XON-43Y to 9 percent for McBee (Table 2). All varieties, except Stansa, and XON-43Y, had bulb pyruvate concentrations low enough (<5.5 pmols/g FW)to be classified as sweet onions. On a scale of to 1, the subjective evaluation of skin retention ranged from the worst of 5 for 'Megane' to the best of 8.6 for Toughball. The percentage of "bullet" single-centered bulbs averaged 5.9 percent and ranged from percent for Megane, Stansa, and XON-43Y to 36.7 percent for McBee. The percentage of functionally single-centered bulbs averaged 27.6 percent and ranged from 4 percent for XON-43Y to 76.3 percent for McBee. 56

67 Table 1. Yield and grade distribution for eight Experiment Station, Oregon State University, onion varieties planted in August 24 Ontario, OR. Marketable yield by grade and harvested in June 25. Malheur Non-marketable yield Seed Plant Total No. company Variety population yield Total >41/4 in >4% in 4-4% in 3-4 in in Total rot 2s Small plants/acre -- cwt/acre -- #/5 lb cwtlacre %oftotal - cwt/acre - A. Takii Hi Keeper 96, Toughball 88, Bejo Megane 69, Olympic 95, Stansa 96, Sakata XON-43Y 79, Scottseed McBee 9, Average 88, LSD (.5) 12, NS Table 2. Maturity, bolting, and bulb quality for eight onion varieties planted in August 24 and harvested in June 25. Maiheur Experiment Station, Orecion State University, Ontario, OR. Functionally single Seed Maturity Bolters Pyruvate Skin Intermediate Small centered "Bullet + company Variety 24-June concentration Sugars retention Blowout double double Bullet small double" % #/plot pmols/g FW % Brix / A. Takil Hi Keeper Bejo Megane Olympic Stansa Sakata XON-43Y Scottseed McBee 9. Average 57.6 LSD (.5) 4.6 *1 = best and = worst NS

68 ONION PRODUCTION FROM SETS Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Introduction Early harvest of quality bulbs at a reasonable production cost would be a strategic marketing advantage. Our earlier research showed that onions can be harvested in July when grown from transplants started in the winter (Shock et al. 24). Transplants must be grown locally due to the onion white rot quarantine that prohibits importation of onion transplants. Onion transplant production in the Treasure Valley of eastern Oregon and western Idaho is expensive due to the need for heated greenhouse production during the winter. Alternatively, over-wintering onions allow early harvest, but the bulb quality of over-wintering onions leaves much to be desired. A third alternative is to produce onion sets in a brief summer season and then use the sets in the following year to establish a crop with the potential of early harvest. However, long-day onions are supposedly unable to form sets and tend to bolt uniformly when grown from bulbs of the previous year. This preliminary trial screened 48 onion varieties to determine their potential to produce sets and whether these sets would bolt or bulb in the successive year. Materials and Methods Onion seed of 48 varieties (Table 1) was planted in plots 4 double rows wide and 27 ft long on May18 and June 1, 24. Seed was planted in double rows spaced 3 inches apart at 33 seeds/ft of single row. Each double row was planted on beds spaced 22 inches apart with a customized planter using John Deere Flexi Planter units equipped with disk openers. Onions from the first planting were lifted on August 23, and were topped and bagged on September 1. Onions from the second planting were lifted on August 3 and topped and bagged on September 9. On October 1, halt of the sets from each planting date were placed in one at two storage rooms. One storage room was maintained at 59 F and the other at 77 F. The relative humidity of both storage rooms was maintained at 7 percent. On March 1, the sets stored at 77 F had the storage temperature reduced to 59 F to delay sprouting. 58

69 On March 16, the sets were removed from storage and sorted into 3 sizes according to bulb diameter: less than 1 inch, inch, and over 1.4 inch. All available sets of each variety from each storage temperature and set size were planted in single separate plots. The sets were manually planted in conventional double rows on 22-inch beds on March 24, 25. The spacing between sets in each single row was 6 inches, equivalent to 95, plants per acre. Due to the small number of available sets of each variety and each size, treatments were not replicated, so this trial was more of a feasibility study. The field was drip irrigated using drip tapes buried at 4-inch depth between the double onion rows. Weeds were controlled with an application of Prowl at 1 lb ai/acre on April 8, Goal at.2 lb ai/acre, Buctril at.3 lb ai/acre, and Poast at.38 lb ai/acre on April 22. The field had 5 lb nitrogen (N)/acre applied on April 28 as N-phuric injected through the drip system. On June 14, 2 lb N/acre as N-phuric and phosphorus (P) at 1 lb/acre as phosphoric acid were injected through the drip system. After lay-by the field was hand weeded as necessary. On July 27 the number of bolted and non-bolted bulbs in each plot was determined. On August 3, the middle two rows in each plot were harvested. The bulbs were graded on August 4. Bulbs were separated according to quality: bulbs without blemishes (No. Is), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Bottytis al/li in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger). The No. I bulbs were graded according to diameter: small (<21/4 inches), medium inches), jumbo (3-4 inches), colossal (4-4% inches), and supercolossal (>4% inches). Bulb counts per 5 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. Varietal and set size differences were compared without ANOVA because treatments were not replicated. Results and Discussion Onions grew very well from seed planted May 18, but not from seed planted June 1. None of the varieties had much bulbing or produced sets from the June 1 planting. Of the 48 varieties planted May 18 (Table 1), 26 produced considerable bulbing and some sets (Table 2). Storage of sets at 59 F resulted in substantial loss of sets compared with 77 F, possibly due to higher relative humidity. Maintenance of the relative humidity at 7 percent at 59 F was not adequate despite the use of a dehumidifier. Storage of sets at 59 F also resulted in substantially more bolting than storage at 77 F (Table 2). The smallest set size (<1 inch) resulted in the least bolting for either storage temperature. The lowest bolting at the 59 F storage temperature was for variety 'Delgado' (2 percent). At the 77 F storage temperature with the smaller than 1-inch set size, varieties 'Daytona' and 'Bandolero' did not bolt. At the 77 F storage temperature with the 1-to 1.4-inch and larger than 1-inch set sizes, variety '41' did not bolt. 59

70 When grown from sets stored at 77 F, a number of varieties produced high yields of large bulbs with little to moderate bolting (Table 3). The exact yield estimate is only approximate due to the very small plot sizes without replication. The partial success of the May 18 planting for set production and the total failure of the June 1 planting for set production suggests that a wide range of planting dates should be tried. Onion plants need to be the right age to bulb during the longest days that precede and follow June 22. Perhaps a May I or April 15 date would be more successful than May 18. References Shock, C.C., E. B. G. Feibert, and L.D. Saunders. 24. Onion production from transplants in the Treasure Valley. Oregon State University Agricultural Experiment Station Special Report 155:

71 Table 1. Long-day onion varieties Experiment Station, Oregon State Seed Company Variety A. Takii T G Bejo Daytona Delgado Gladstone Redwing BGS 196 Fl Crookham Harmony OLYS97-24 OLYS97-27 XPH95345 Long Harvest Moon D. Palmer Mesquite Tequfla Rispens Export 151 Brite Knight Red Fortress Scottseed Oro Blanco Seedworks Varsity Seminis Exacta Golden Spike Mercury Red Zepelin Santa Fe Vision Quest PX 2599 PX 5299 SVR 716 SVR 5646 SVR 5819 Nunhems Bandolero Granero Pandero Ranchero Sabroso Salsa Tesoro Torero Vaquero SX74 ON Aquila Renegade Cometa planted in 24 for set production, University, Ontario, OR. 61

72 Table 2. Influence of onion set storage temperature and set size on bolting by long-day onion varietles. Maiheur Experiment Station, Oregon State University, Ontario, OR. Seed Company Storage at 59 F Storage at 77 F Variety <1 inch inch >1.4 inch % of bolted bulbs <1 inch inch >1.4 inch % of bolted bulbs A. Takii T T Bejo Daytona Delgado Gladstone BGS 196 Fl Crookham OLYS XPH Dorsing Harvest Moon D. Palmer Tequila Rispens Export Seedworks Varsity Seminis Santa Fe PX Nunhems Bandolero Ranchero Sabroso Salsa Vaquero Aquila Renegade Cometa Seminis Exacta Golden Spike Average

73 Table 3. Performance data for onion varieties grown from sets stored at 77 F and having less than 2 percent bolting*. The confidence of yield estimates is low, because of the small plot sizes and lack of replication. Maiheur Experiment Station, Oregon State University, Ontario, OR. Marketable yield by grade Seed Total Bulb company Variety Bolting yield Total >4V4 in in 3-4 in 21h-3 in counts >41/ in Double Small % cwt/acre #/5 lb -- cwt/acre -- <1 inch set size A. Takii T T Bejo Daytona Delgado Seminis Santa Fe ,41.6 1, Nunhems Bandolero Vaquero 9.4 1, , , Seminis Exacta 7.7 1, , Golden Spike inch set size A. Takil T T Seedworks Nunhems Bandolero Ranchero ,15.5 1, >1.4 inch set size Seedworks Nunhems Bandolero *yields of varieties and set sizes with bolting greater than 2 percent are not reported. 63

74 ONION PRODUCTION FROM FIELD-GROWN TRANSPLANTS Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Introduction Our earlier research showed that onions can be harvested in July when grown from transplants started in the winter (Shock et at. 24). Transplants must be grown locally due to the marketing order onion white rot quarantine that prohibits importation of onion transplants. Onion transplant production in the Treasure Valley of eastern Oregon and western Idaho is expensive due to the need for heated greenhouse production during the winter. In order to make early onion production from transplants cost effective, we hypothesized that transplants might be produced by growing transplants outdoors in late summer at a high density and transplant them either in the fall or in March. The problem with this alternative is that no one had ever done this, so we had no idea whether or not it could work. Materials and Methods The transplants were grown from seed in a field of Greenleaf silt loam during the fall and winter of Onion seed of 7 overwintering varieties was planted in plots 4 double rows wide and 27 ft long on August 3, 24. Seed was planted in double rows spaced 3 inches apart at 21 seeds/ft of single row. Each double row was planted on beds spaced 22 inches apart with a customized planter using John Deere Flexi Planter units equipped with disk openers. Roundup at 1 lb ai/acre was applied in 32 gal/acre of water on September 8. Emergence started on September 1. Repeated insecticide applications were needed to control thrips. On September 11, the onions were sprayed with Malathion at 1 lb ai/acre. On September 17, the onions were sprayed with Malathion at 2 lb ai/acre. On September 23 and October 4 the onions were sprayed with Warrior at.3 lb ai/acre. On October 4, Buctril at.12 lb ai/acre and Poast at.28 lb ai/acre were applied to control weeds. Due to unusually wet weather during the fall of 24, fall transplanting was not possible. On March 9 and 1 the seedlings were transplanted to a field of Nyssa-Malheur silt loam. The seedlings were manually dug up and planted in double rows on 22-inch beds. The spacing between plants in each single row was 6 inches, equivalent to 95, plants per acre. Plots of each variety were 2 ft long by 4 double rows wide arranged in a randomized complete block design with five replicates. The field was drip irrigated on March 1 using drip tapes buried at 4-inch depth between the double onion 64

75 rows. Thereafter the trial was irrigated when the soil water tension at 8-inch depth reached 2 cb. Soil water tension was monitored by six granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 2SS, Irrometer Co., Riverside, CA) installed below the onion row at 8-inch depth. Weeds were controlled with an application of Prowl at 1 lb ai/acre on April 8, and Goal at.2 lb al/acre, Buctril at.3 lb al/acre, and Poast at.38 lb al/acre on April 22. A root tissue sample taken on June 9 showed the need for nitrogen (N) and phosphorus (P). The field had 5 lb NI/acre applied on April 28 as NI-phuric injected through the drip system. On June 14, 2 lb N/acre as N-phuric and P at 1 lb/acre as phosphoric acid were injected through the drip system. After lay-by the field was hand weeded as necessary. On July 7 and again on July 26, 9.5 ft of the middle two rows in each plot were topped and bagged. Decomposed bulbs were not bagged. The onions from the first and second harvests were graded on July 8 and July 27, respectively. Bulbs were separated according to quality: bulbs without blemishes (No. is), split bulbs (No. 2s), bulbs infected with neck rot (Botrytis al/il) in the neck or side, plate rot (Fusarium oxysporum), or black mold (Aspergillus niger). The No. I bulbs were graded according to diameter: small (<2% inches), medium inches), jumbo (3-4 inches), colossal (4-4% inches), and supercolossal (>4% inches). Bulb counts per 5 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all super colossal bulbs during grading. Ten randomly chosen bulbs from every plot of the three highest yielding varieties from the July 7 and July 26 harvests were shipped on July 29 via UPS ground to Vidalia Labs International in Collins, Georgia. The bulb samples were analyzed for pyruvic acid content on August 5. Bulb pyruvic acid content is a measure of pungency with the unit being micro mols pyruvic acid per gram of fresh weight (pmols/g FW). Onion bulbs having a pyruvate concentration of 5.5 micro mols or less are considered sweet according to Vidalia Labs sweet onion certification specifications. On August 2 onion bulbs from the July 26 harvest were rated for single centers. The onions from each plot were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured. These multiple-centered onions were ranked according to the diameter of the first single ring: "small double" had diameters less than 11/2 inch, "intermediate double" had diameters from 11/2 to 2% inches, and "blowout" had diameters over 2% inches. Single-centered onions were classed as a "bullet". Onions were considered "functionally single centered" for processing if they were a "bullet" or "small double". Varietal differences were compared using ANOVA and protected least significant differences at the 5 percent probability level, LSD (.5). 65

76 Results and Discussion Onions for transplants grew very well in 24. It was our intention to transplant onions in October of 24 as well as March of 25, but rainy weather in October of 24 did not allow field operations or fall transplanting. July 7 harvest Varieties 'Megane' and 'Stansa' were among the varieties with the highest total and marketable yield from the July 7 harvest (Table 1). Megane had the highest colossal onion yield. Megane and Stansa had pyruvate concentration low enough (5.5 or less) to be considered "sweet" according to Vidalia Labs sweet onion certification specifications (Table 2). 'McBee' had the highest percentage of "bullet" single-centered bulbs. McBee and 'Hi Keeper' had among the highest percentage of functionally single-centered bulbs. Hi Keeper, 'Toughball', 'Olympic', and McBee had maturity ratings above 6 percent on July 5 and were terminated at the July 7 harvest. July 26 harvest The July 26 harvest included Megane, Stansa, and 'XON-43Y'. Megane and Stansa had the highest total and marketable yield (Table 1). Megane and Stansa also had the highest jumbo onion yield. Only Megane and Stansa had pyruvate concentration low enough (5.5 or less) to be considered "sweet". References Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 24. Onion production from transplants in the Treasure Valley. Oregon State University Agricultural Experiment Station Special Report 155:

77 Table 1. Performance data for experimental and commercial onion varieties produced from field-grown transplants and harvested on July 7, and July 26, 25, Malheur Experiment Station, Oregon State University, Ontario, OR. Seed Total Marketable yield by grade Non-marketable yield Maturity arie y company yield Total 4-4Y4 in 3-4 in in No. 2s Small July 5 Bolters cwtlacre -- cwtlacre -- % #/plot July 7 A.Takii HiKeeper Toughball Bejo Megane Olympic Stansa Sakata XON-43Y Scottseed McBee LSD (.5) July 26 Bejo Megane Stansa Sakata XON-43Y LSD (.5) NS NS NS NS Table 2. Pyruvate concentrations and multiple center rating for selected onion varieties produced from field-grown transplants, Malheur Experiment Station, Oregon State University, Ontario, OR. Pyruvate Functionally single Seed concentration "Intermediate "Small centered "small company Variety July 7 July 26 "Blowout" double" double" "Bullet" double + bullet" pmols/g FW / A. Takii Hi Keeper Toughball Bejo Megane Olympic Stansa Sakata XON-43Y Scottseed McBee LSD (.5) *na not available. na* na 5.3 na na.31 na na 4.68 na na

78 AUTOMATIC COLLECTION, RADIO TRANSMISSION, AND USE OF SOIL WATER DATA1 Clinton C. Shock, Erik B. C. Feibert, Rebecca Flock, Cedric A. Shock, and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Abstract Precise scheduling of drip irrigation has become very important to help assure optimum crop yield and quality. Soil moisture sensors have often been adopted to assure irrigation management. Integrated systems that use soil moisture data for irrigation management could enhance widespread applicability of soil moisture-based irrigation management. An ideal system would include the equipment to monitor field conditions, radios to transmit the information from the field, interpretation of soil water status, and the equipment to automatically control irrigation systems. Radio transmission of data would be advantageous because wires impede cultivation and complicate cultural practices. Key words: automation, irrigation scheduling, onion, A/hum cepa Introduction Onions (A/hum cepa) require frequent irrigations to maintain high soil moisture. Drip irrigation has become popular for onion production because a higher soil moisture can be maintained without the negative effects associated with furrow irrigation. Drip irrigation can also be automated. Automated drip irrigation of onions has been used for irrigation management research at the Malheur Experiment Station since 1995 (Feibert et at. 1996; Shock et al. 1996, 22). However, the extensive wiring impedes cultivation and can complicate cultural practices. Several companies manufacture automated irrigation systems designed for commercial use that use radio telemetry, reducing the need for wiring. This trial tested three commercial soil moisture monitoring systems and compared their performance to the research system based on Campbell Scientific (Logan, UT) components currently used (Shock et al. 22). Materials and Methods The onions were grown at the Malheur Experiment Station (MES), Ontario, Oregon, on an Owyhee silt loam previously planted to wheat. Onion (cv. 'Vaquero', Nunhems, Parma, ID) was planted in 2 double rows, spaced 22 inches apart (center of double row 1 This report is provided as a courtesy to onion growers. This work was supported by sources other than the Idaho-Eastern Oregon Onion Committee. 68

79 to center of double row) on 44-inch beds on March 16, 25. The 2 rows in the double row were spaced 3 inches apart. Onion was planted at 15, seeds/acre. Drip tape (T-tape, T-systems International, San Diego, CA) was laid at 4-inch depth between the 2 double onion rows at the same time as planting. The distance between the tape and the center of the double row was 11 inches. The drip tape had emitters spaced 12 inches apart and a flow rate of.22 gal/mm/i ft. Onion emergence started on April 17. The trial was irrigated with a minisprmnkler system (RIO Turbo Rotator, Nelson Irrigation Corp., Walla Walla, WA) for even stand establishment. Risers were spaced 25 ft apart along the flexible polyethylene hose laterals that were spaced 3 ft apart. Weed and insect control practices were similar to typical crop production standards and fertilizer applications were similar to common practices and followed the recommendations of Sullivan et al. (21). The experimental design was a randomized complete block with three replicates. Each irrigation system was tested in 3 zones that were 8 rows wide by 5 ft long. There were four automated irrigation systems tested. Each integrated system contained several distinctive parts, some completely automated and some requiring manual input: soil moisture monitoring, data transmission from the field, collection of the data, interpretation of the data, decisions to irrigate, and control of the irrigation. All data were downloaded for evaluation of the system. Campbell Scientific The system currently used for research at MES uses a Campbell Scientific Inc. (Logan, UT) datalogger (CRIOX). Each zone had four granular matrix sensors (GMS, Watermark Soil Moisture Sensor Model 2SS, Irrometer Co. Inc., Riverside, CA) used to measure soil water potential (SWP) (Shock 23). The GMS from all three zones were connected to an AM416 multiplexer (Campbell Scientific), which in turn was connected to the datalogger at the field edge. The soil temperature was also monitored and was used to correct the SWP calibrations (Shock et al. 1998a). The datalogger was programmed to monitor the soil moisture and controlled the irrigations for each zone individually. The Campbell Scientific datalogger was programmed to make irrigation decisions every 12 hours. Zones were irrigated for 8 hours if the SWP threshold was exceeded. The Campbell Scientific datalogger used an average SWP at 8-inch depth of -2 kpa or less as the irrigation threshold (Shock et al b, 2). The datalogger controlled the irrigations using an SDMI6 controller (Campbell Scientific) to which the solenoid valves at each zone were connected. The datalogger was powered by a solar panel and the controller was powered by 24 V AC. Data were downloaded from the datalogger with a laptop computer or with an SM192 Storage Module (Campbell Scientific) and a CR1 OKD keyboard display (Campbell Scientific). Automata Each one of the three zones in the Automata system (Automata, Inc., Nevada City, CA) had four GMS connected to a datalogger (Mini Field Station, Automata). The 69

80 dataloggers at each zone were connected to a controller (Mini-P Field Station, Automata) at the field edge by an internal radio; the controllers were connected to a base station (Mini-P Base Station, Automata) in the office by radio. The base station was connected to a desktop computer. Each zone was irrigated individually using a solenoid valve, which was connected to and controlled by the controller. The desktop computer ran the software that monitored the soil moisture in each zone and made the irrigation decisions every 12 hours. Zones were irrigated for 8 hours if the SWP threshold was exceeded. The irrigation threshold was the average SWP at 8-inch depth of -2 kpa or less. The Mini Field Stations were powered by solar panels and the Mini-P Field Station was powered by 12 V AC. Watermark Monitor Irrometer manufactures the Watermark Monitor datalogger that can record data from seven GMS and one temperature probe. The soil temperature is used to correct the SWP calibrations. Each of the three Watermark Monitor zones had seven GMS connected to a Watermark Monitor. Data were downloaded from the Watermark Monitor both by radio and with a laptop computer. The Watermark Monitors were powered by solar panels. Irrigation decisions were made daily by reading the GMS data from each Watermark Monitor. When the SWP reached -2 kpa the zone was irrigated manually for 8 hours. A cclima Acclima (Meridian, ID) manufactures a Digital TDTTM that measures volumetric soil moisture content. Each zone had one TDT sensor and four GMS. The TDT sensors were connected to a model CS35 controller (Accllma) at the field edge. The controller monitored the soil moisture and controlled the irrigations for each zone separately using solenoid valves. The controller was powered by 12 V AC. Data were downloaded from the controller using a laptop computer. For comparison and calibration, the GMS were connected to the Campbell Scientific datalogger, which monitored the SWP as described above. The CS35 controller was programmed to irrigate the zone when the volumetric soil water content was equal to or lower than a preset value. The SWP data were compared to the volumetric soil water content data to adjust the CS35 controller to irrigate each zone in a manner equivalent to the irrigation scheduling at -2 kpa (Fig. 1). All Systems All soil moisture sensors in every zone of the four systems were installed at 8-inch depth in the center of the double onion row. The GMS were calibrated to SWP (Shock et al. 1998a). The Campbell Scientific, Acclima, and Automata controllers were programmed to make irrigation decisions every 12 hours. Zones were irrigated for 8 hours if the soil moisture threshold in that zone was exceeded. The Campbell Scientific and Automata dataloggers used an average SWP at 8-inch depth of -2 kpa or less as the irrigation threshold. The Irrometer zones also had a threshold of -2 kpa. The amount of water applied to each plot was recorded daily at 8: a.m. from a water meter installed downstream of the solenoid valve. The total amount of water applied 7

81 included sprinkler irrigations applied after emergence and water applied with the drip-irrigation system from emergence through the final irrigation. Onion evapotranspiration (EL) was calculated with a modified Penman equation (Wright 1982) using data collected at the MES by an AgriMet weather station (U.S. Bureau of Reclamation, Boise, ID). Onion was estimated and recorded from crop emergence until the onions were lifted on September 12. On September 12 the onions were lifted to field cure. On September 19, onions in the central 4 ft of the middle 4 double rows in each zone were topped and bagged. On October 3 the onions were graded. Bulbs were separated according to quality: bulbs without blemishes (No. is), double bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis al/il in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergil/us niger). The No. I bulbs were graded according to diameter: small (<2% inch), medium inch), jumbo (3-4 inch), colossal (4-4% inch), and supercolossal (>4% inch). Bulb counts per 5 lb of supercolossal onions were determined for each zone of every variety by weighing and counting all supercolossal bulbs during grading. Differences in onion performance and water application among irrigation systems were determined by protected least significant differences at the 95 percent confidence level using analysis of variance (Hintze 2). Results and Discussion All systems maintained the SWP close to the target of -2 kpa (Figures 2 and 4). The Campbell Scientific system had the smallest amplitude of oscillation of SWP around -2 kpa compared to the other systems. The Automata system had wide oscillations in SWP compared to the Campbell Scientific system. The Automata system had impaired communication between the office computer and the field datalogger, hindering the irrigation automation. The impaired communication of the Automata system may have been caused by interference from other automated communication systems being tested concurrently. Marketable onion yield in 25 was lower than in 24 for all systems, averaging 751 cwtlacre over the 4 drip irrigation systems, compared to the average of 1,41 cwtlacre in 24 (Table 1). Factors possibly causing the lower yield in 25 were spring bedded ground, lack of fumigation, slower seed emergence, delayed weed control due to excessive rain in May, heavy thrips pressure, and the presence of iris yellow spot virus. Due to excessive rain in the fall of 24, the field work was delayed until early March of 25. Fall bedding results in better soil tilth than spring bedding. In addition, spring field work precluded soil fumigation, leaving the onions more vulnerable to soil borne diseases. Onions took 32 days to emerge in 25 compared to the previous 8-year average of 17 days for drip-irrigated onions at the MES. Despite planting occurring a day earlier in 25 than in 24, emergence in 25 started 15 days later than in

82 Excessive rain in late April and May delayed weed control, resulting in excessive weed competition during a period of intense onion vegetative growth. A comparison of the systems in terms of onion yield and grade is not completely justified because the systems were started at different times. In addition, the Accilma system required adjustments after the start of operation. The Irrometer system resulted in the lowest colossal bulb yield and the highest medium bulb yield in 25, possibly due to human collection of the SWP data and human control of irrigation onset and duration. There was no significant difference in yield or grade between the other systems. Water applications over time followed during the season (Fig. 5). Total amounts of water applied were substantially higher than for all systems except the Irrometer system. The higher amounts of water applied in 25 than in 24 could be related to the lower saturated hydraulic conductivity of the soil in 25. A lower saturated hydraulic conductivity would result in more water being necessary to maintain the sensors wet. The total water applied plus precipitation from emergence to the end of irrigation on September 5 was 48.2, 32.6, 45.3, and 57.6 inches for the Campbell Scientific, lrrometer, Acclima, and Automata systems, respectively. Precipitation from onion emergence until irrigation ended on September 5 was 4.8 inches. Total for the season was 35. inches from emergence to lifting. References Feibert, E.B.G., C.C. Shock, and L.D. Saunders Plant population for drip-irrigated onions. Oregon State University Agricultural Experiment Station Special Report 964: Hintze, J.L. 2. NCSS 97 Statistical System for Windows, Number Cruncher Statistical Systems, Kaysville, UT. Shock, C.C. 23. Soil water potential measurement by granular matrix sensors. Pages in B.A. Stewart and T.A. I lowell The Encyclopedia of Water Science. Marcel Dekker. Shock, C.C., J. Barnum, and M. Seddigh. 1998a. Calibration of Watermark soil moisture sensors for irrigation management. Pages in Proceedings of the International Irrigation Show. Irrigation Association. San Diego, CA. Shock, C.C., E.B.G. Feibert, and L.D. Saunders Nitrogen fertilization for drip-irrigated onions. Oregon State University Agricultural Experiment Station Special Report 964: Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 1998b. Onion yield and quality affected by soil water potential as irrigation threshold. HortScience 33:

83 Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2. Irrigation criteria for drip-irrigated onions. HortScience 35: Shock, C.C., E.B.G. Feibert, L.D. Saunders, and E.P. Eldredge. 22. Automation of subsurface drip irrigation for crop research. Pages in American Society of Agricultural Engineers, World Congress on Computers in Agriculture and Natural Resources. lguaçu Falls, Brazil. Sullivan, D.M., B.D. Brown, C.C. Shock, D.A. Horneck, R.G. Stevens, G.Q. Pelter, and E.B.G. Feibert. 21. Nutrient management for onions in the Pacific Northwest. Pubi. PNW 546. Pacific Northwest Ext., Oregon State University, Corvallis, OR. Wright, J.L New evapotranspiration crop coefficients. J. lrrig. Drain. Div. ASCE 18:

84 Table 1. Onion yield and grade for a drip-irrigated onion field irrigated using four soil moisture monitoring and control systems, Oregon State University, Malheur Experiment Station, Ontario, OR, 24 and 25. Total Marketable yield by grade Supercooss: System yield Total >41/4 in 4-41h in 3-4 in 21h-3 in Small No. 2s cwtlacre #/5 lb -- cwt/acre Campbell Sci. 1,35.9 1, Acclima 1, Automata 1,72.4 1, lrrometer 1,81.4 1, Average 1,49.5 1, LSD (.5) NS 86.5 NS NS NS NS NS 25 Campbell Sci Acclima Automata Irrometer Average LSD (.5) NS NS NS 47.7 NS 26.1 NS NS NS Average Campbell Sci Acclima Automata lrrometer

85 -1 Irrigation threshold: 13% Y= X R2 =.5, P = Volumetric soil water content, % - Irrigation threshold: 12% then C a) -1 a) Y = X X2 R2 =.79, P = Volumetric soil water content, % C 4- a) 4- C/) Irrigation threshold: 16% I. Y= X - R2.18,P Volumetric soil water content, % Figure 1. Regressions of volumetric soil water content from Accilma TDT sensors against soil water potential from Watermark soil moisture sensors for each Acclima plot. Maiheur Experiment Station, Oregon State University, Ontario OR. 75

86 CD a. 5 CD ci) - ci) 3 CD -4 Irrigation threshold 12% then 16% Day of year Figure 2. Soil water potential at 8-inch depth for a drip-irrigated onion field using the Acclima automated irrigation system with 3 volumetric soil water content irrigation thresholds, Oregon State University, Maiheur Experiment Station, Ontario, OR

87 3 a) C C.) a) 2 ci) E > 1 Irrigation threshold: 13% Day of year C a) C S a) 2 (I) C.) a) E > Day of year 3 C ci) C C.) a) 2 C,, C) a) E > 1 Irrigation threshold: 16% Day of year Figure 3. Volumetric soil water content at 8-inch depth for a drip-irrigated onion field using the Acclima irrigation system with 3 soil water content irrigation thresholds, Oregon State University, Malheur Experiment Station, Ontario, OR

88 -1 - Campbell Scientific Co c -1 ci) o -2 Automata Day of year Irrometer 25 Figure 4. Soil water potential at 8-inch depth for a drip-irrigated onion field using 3 soil moisture monitoring and control systems, Oregon State University, Maiheur Experiment Station, Ontario, OR

89 6 4 Campbell Scientific (I) a) 2 6 I rrorrieter U) = 4 Acclima Day of year Figure 5. Water applied plus precipitation and over time for drip-irrigated onions with 4 soil moisture monitoring and control systems. Thick line is water applied and thin line is ETC, Oregon State University, Maiheur Experiment Station, Ontario, OR

90 SHORT-DURATION WATER STRESS DECREASES ONION SINGLE CENTERS WITHOUT CAUSING TRANSLUCENT SCALE Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders Maiheur Experiment Station Oregon State University Ontario, OR Introduction In earlier trials we have shown that onion yield and grade are very responsive to careful irrigation scheduling and maintenance of optimum soil moisture (Shock et al. 1998b, 2). Using a high-frequency automated drip-irrigation system, the soil water tension at 8-inch depth that resulted in maximum onion yield, grade, and quality after storage was determined to be no drier than 2 cbars. It is not known whether short-term water stress, caused by irrigation errors, could result in internal bulb defects such as multiple centers and translucent scale. This trial tested the effects of short-duration water stress at different times early in the season on onion single centeredness and translucent scale. Materials and Methods Onions were grown at the Malheur Experiment Station, Ontario, Oregon on an Owyhee silt loam previously planted to wheat. In the fall of 24, the wheat stubble was shredded, and the field was irrigated and disked. A soil analysis on September 14, 24, showed a ph of 7.7, 2.4 percent organic matter, 36 ppm P, 764 ppm K, 4266 ppm calcium, 94 ppm magnesium (Mg), 3.1 ppm zinc (Zn), 15 ppm iron, 79 ppm manganese, 1.8 ppm copper, and.7 ppm boron (B). The soil was fertilized with 1 lb phosphate/acre, 4 lb sulfur/acre, and 4 lb Zn/acre, which were broadcast in the fall of 24 after disking. The field was not fumigated nor bedded in the fall due to excessive moisture. In early March 25, the field was moldboard-plowed, groundhogged, roller-harrowed, and bedded. Onion seed was planted at 15, seeds/acre in 2 double rows, spaced 22 inches apart (center to center of double rows) on 44-inch beds on March 16, 25. The 2 rows in the double row were spaced 3 inches apart. Drip tape (T-tape, T-systems International, San Diego, CA) was laid at 4-inch depth between the 2 double onion rows simultaneously with planting. The distance between the tape and the center of the double row was 11 inches. The 6-mil drip tape had emitters spaced 12 inches apart and a nominal flow rate of.22 gal/mm/lou ft at 1 PSI. Immediately after planting the onion rows received 3.7 oz of Lorsban I 5G per 1, ft of row (.82 lb ai/acre), and the soil surface was rolled. The trial was irrigated for even stand establishment on April 13 and April 15 with a minisprinkler system (RIO Turbo 8

91 Rotator, Nelson Irrigation Corp., Walla Walla, WA). Risers were spaced 25 ft apart along the flexible polyethylene hose and hoses were spaced 3 ft apart. The water application rate was.1 inch/hour. Onion emergence started on April 17. The experimental design had six irrigation treatments arranged in a randomized complete block with five replicates. The six drip-irrigated treatments consisted of five timings of short-duration water stress and an unstressed check. Two varieties ('Vaquero', Nunhems, Parma, ID and '611', Global Genetics, Payette, ID) were split plots within the main irrigation treatment plots. Each irrigation treatment main plot was 4 double rows by 6 ft and each variety subplot was 4 double rows by 3 ft. Each plot had a ball valve allowing manual control of irrigations. The water stress was applied by turning the water off manually to all plots in a given treatment until the average soil water tension at 8-inch depth for the treatment reached 6 cbars; at this point, the irrigation to all plots in that treatment was turned on again. Except for the unstressed check treatment, the onions in each treatment were stressed only once during the season. The five timings for the stress treatments were: two-leaf stage, four-leaf stage (water off May 27, water back on June 2), early six-leaf stage (water off June 13, water back on June 29), late six-leaf stage (water off June 2, water back on June 3), and eight-leaf stage (water off June 28, water back on July 11). Soil water tension (SWT) was measured in each plot with four granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 2SS, Irrometer Co. Inc., Riverside, CA) installed at 8-inch depth in the center of the double row. Sensors had been previously calibrated to SWT (Shock et al. 1998a). The GMS were connected to the datalogger with three multiplexers (AM 41 multiplexer, Campbell Scientific, Logan, UT). The datalogger read the sensors and recorded the SWT every hour. The irrigations were controlled by the datalogger using a relay driver (A21 REL, Campbell Scientific, Logan, UT) connected to a solenoid valve. Irrigation decisions were made every 12 hours by the datalogger as follows: if the average SWT at 8-inch depth in the unstressed treatment plots was 2 cbars or more the field was irrigated for 4 hours. If the SWT was less than 2 cbars, the field was not irrigated. The pressure in the drip lines was maintained at 1 psi by a pressure regulator. Irrigations ended on September 5. The field had Prowl (1 lb ai/acre) broadcast on May 23 for postemergence weed control. Approximately.45 inch of water was applied through the minisprinkler system on May24 to incorporate the Prowl. Goal at.16 lb ai/acre, Buctril at.16 lb ai/acre, and Poast at.21 lb aifacre were applied on May 27 for weed control. Due to high rainfall in April and May, Bravo at 2.25 lb ai/acre was applied on May 2 for prevention of foliar fungal diseases. Onion tissue was sampled for nutrient content on June 8. In each check plot, the roots from four onion plants from one of the border rows of variety Vaquero were washed with deionized water, bulked together, and analyzed for nutrient content by Western 81

92 Labs, Parma, Idaho. The onions in all treatments were fertilized according to the plant nutrient analyses. Urea ammonium nitrate solution at 6 lb N/acre, P at 1 lb/acre as phosphoric acid, K at 2 lb/acre as potassium chloride, and Mg at 5 lb/acre as Epsom salts (magnesium sulfate) were applied through the drip tape on June 15. Nitrogen at 4 lb/acre as urea ammonium nitrate solution was injected through the drip tape on June 2. A second tissue sample taken on July 11 showed the need for B. On July 14, B at.2 lb/acre as boric acid was injected through the drip tape. Thrips populations were very challenging in 25. Thrips were controlled with aerial applications of the following insecticides: June 16, Warrior plus Lannate ; June 24, Warrior ; July 1, Warrior plus Lannate; July 18, Warrior plus Lannate; July 26, Warrior plus MSR; August 3, Warrior plus Lannate; August 1, Warrior plus MSR; August 14, Warrior plus Lannate; August 2, Warrior plus MSR. Warrior was applied at.3 lb ai/acre, Lannate at.45 lb ai/acre, and MSR at.5 lb ai/acre. On September 12 the onions were lifted to cure. On September 19, onions in the central 25 ft of the middle 2 double rows in each subplot were topped and bagged. The bags were placed into storage on September 22. The storage shed was managed to maintain air temperature at approximately 34 F. The onions were graded on December 8, 25. Bulbs were separated according to quality: bulbs without blemishes (No. Is), double bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis al/il in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergil/us niger). The No. 1 bulbs were graded according to diameter: small (<2.25 inches), medium ( inches), jumbo (3-4 inches), colossal ( inches), and supercolossal (>4.25 inches). Bulb counts per 5 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. After grading, 5 bulbs ranging in diameter from 3.5 to 4.25 inches from each subplot were rated for single centers and translucent scale. The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured. These multiple-centered onions were ranked according to the diameter of the first single ring: "small doubles" have diameters less than 1.5 inches, "intermediate doubles" have diameters from 1.5 to 2.25 inches, and "blowouts" have diameters greater than 2.25 inches. Single-centered onions are classed as a "bullet". Onions are considered functionally single centered for processing if they are a "bullet" or "small double." The number and location of translucent scales in each bulb was also recorded. The data were analyzed using analysis of variance and treatment means were compared using the protected least significant difference test at the 5 percent probability level, LSD (.5). Treatment means were considered statistically different if the difference between means was equal to or greater than the LSD value for a characteristic. 82

93 Results Excessive rainfatl in April and May prevented water stress at the two-leaf stage. Single Centeredness - Vaquero Water stress at the four-leaf stage resulted in the lowest percentage of single-centered or functionally single-centered onions. Water stress at the six-leaf early or six-leaf late stages resulted in more single-centered or functionally single-centered onions than at the four-leaf stage, but less than the unstressed check (Table 1). Water stress at the four-leaf stage resulted in the highest percentage of blowout multiple-centered onions. Water stress at the eight-leaf stage did not result in fewer functionally single-centered bulbs than the unstressed check. Single Centeredness Water stress at the four-leaf or six-leaf early stages resulted in the lowest percentage of single-centered onions. Water stress at the six-leaf late stage resulted in more single-centered onions than at the four-leaf or six-leaf early stages, but less than the unstressed check. Water stress at the four-leaf or six-leaf early stages resulted in the lowest percentage of functionally single-centered onions. Water stress at the six-leaf late and eight-leaf stages did not result in fewer functionally single-centered bulbs. Single Centeredness - Variety Average Compared to the unstressed check, water stress resulted in decreasing percentages of single-centered and functionally single-centered bulbs in the following order of timing: six-leaf late, six-leaf early, and four-leaf stage. Translucent Scale There was no significant difference between treatments in the percentage of bulbs with translucent scale. The percentage of bulbs with translucent scales was small from all treatments. Previous research has shown that factors other than water stress can cause translucent scale, such as prolonged field curing and high artificial drying temperatures (Solberg and Boe 1997). Yield and Grade The interaction effects of stress treatment and variety were not statistically significant, so the stress treatment effects are discussed in terms of the variety averages. Total and marketable onion yield were reduced substantially by water stress at the eight-leaf stage (Table 2). Reductions in supercolossal onion yield resulted from water stress at the four-leaf, six-leaf late, and eight-leaf stages. Reductions in colossal onion yield resulted from water stress at the six-leaf early, six-leaf late, and eight-leaf stages. Variety Comparison Variety 611 had more single-centered and functionally single-centered onions than Vaquero. Vaquero had more pronounced reductions in single centered and functionally single-centered onions in response to water stress than 611. Vaquero had higher total and marketable yield than 611. Variety 611 had higher colossal onion yield than 83

94 Vaquero. It is possible that the lower yield of 611 observed in this trial was associated with onion thrips pressure. Discussion In 23, water stress at the four-leaf and six-leaf early stages resulted in significantly lower single-centered and functionally single-centered bulbs than the unstressed check (Shock et al. 24). In 24, water stress did not affect onion single centeredness (Shock et al. 25). Both average maximum air and 4-inch soil temperatures during the stress treatments were higher in 23, lower in 25, and lowest in 24 (Table 3). The lack of response of single centeredness to water stress in 24 could be related to the lower temperatures during the water stress treatments. Water stress alone during a period of cool and overcast or rainy weather might have a smaller effect on stopping onion growth than stress during warmer, drier weather. The clear response of single centeredness to water stress in 25 is somewhat surprising, because temperatures were only slightly higher than in 24 and substantial precipitation occurred in 25 (Table 4). The precipitation during the stress treatments in 25 explains the longer duration of the stress treatments than in 24 and 23. At each stress timing, more days of water stress were required for SWT to reach 6 cbars in 25 than in 24 or 23 (Fig. 1, Tables 3 and 4). The longer stress periods in 25 also resulted in a longer period of SWT above 4 cbars in 25 than in 23 and 24. The longer duration of stress in 25 might explain why stress at the six-leaf late stage had an effect on single centeredness in 25 and not in 23 and 24. Also, the longer duration of stress in 25 might explain the effect of stress on yield. Prior work has shown that extended SWT drier than 2 cbars reduces onion marketable yield (Shock et al. 2). The effect of stress on yield was more pronounced at the eight-leaf stage, which is the beginning of bulb growth. The 23 and 25 results show that onions are more susceptible to producing multiple centers when stressed at the four-leaf and six-leaf early stages than later at the six-leaf late and eight-leaf stages. Over the 3 years, the four-leaf and early six-leaf stages occurred from late May through June. References Shock, C.C., J.M. Barnum, and M. Seddigh. 1998a. Calibration of Watermark Soil Moisture Sensors for irrigation management. Pages in Proceedings of the International Irrigation Show, Irrigation Association, San Diego, CA. Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 1998b. Onion yield and quality affected by soil water potential as irrigation threshold. HortScience 33: Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2. Irrigation criteria for drip-irrigated onions. HortScience 35:

95 Shock, C.C., E. Feibert, and L. Saunders. 24. Effect of short duration water stress on onion single centeredness and translucent scale. Oregon State University Agricultural Experiment Station Special Report 155: Shock, C.C., E. Feibert, and L. Saunders. 25. Effect of short duration water stress on onion single centeredness and translucent scale. Oregon State University Agricultural Experiment Station Special Report 162: Solberg, S.O. and E. Boe The influence of crop management on watery scales in onions - a survey in southeastern Norway. In: Translucent and leathery scales in bulb onions (A/hum cepa L). Norwegian Crop Research Institute, Doctor Scientarum Theses 3. 85

96 Table 1. Onion multiple-center rating and translucent scale response to timing of water stress for two varieties, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Functionally single centered bullet+srnall Translucent Water stress timing Blowout* Intermethate Vaquero / Bullets Check, no stress leaf stage leaf stage leafearlystage leaf late stage leaf stage Average Check, no stress leaf stage leaf stage leafearlystage leaf late stage leaf stage Average Variety average Check, no stress leaf stage leaf stage leafearlystage leaf late stage leaf stage Average LSD (.5) Treatment NS Variety NS 2. NS NS Treatment X variety NS NS *Blowout: diameter of the first single ring >21/4 inches. tlntermediate double: diameter of the first single ring 1 %-2V4 inches. double: diameter of the first single ring <1 1/2 inches. single-centered. 86

97 Table 2. Onion yield and grade response to timing of water stress for two varieties, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Marketable yield by grade Bulb Nonmarketable yield Total Water stress timing Total >4% in 4-4% in 3-4 in 21h-3 in Total rot Small cwtlacre #/5 lb % of total -- cwt/acre -- Vaguero Check, no stress leaf stage leaf stage leaf early stage leaf late stage leaf stage Average Check,nostress leaf stage leaf stage leafearlystage leaf latestage leaf stage Average Variety average Check, no stress leaf stage leaf stage leaf early stage leaf late stage leaf stage Average LSD (.5) Treatment NS NS NS 3.7 Variety NS NS NS NS NS Treatment X variety NS NS NS NS NS NS NS NS NS NS 87

98 CD ci) (I) check, no stress - 2 leaf stress 4 leaf stress Day of year Figure 1. Soil water tension for onions irrigated at 2 cbars with an automated drip-irrigation system and submitted to short-duration water stress, Maiheur Experiment Station, Oregon State University, Ontario, OR,

99 Table 3. Degree days (32-14 F), average maximum 4-inch soil temperature, and average maximum air temperature during stress treatments, Malheur Experiment Station, Oregon State University, Ontario, OR. Water stress Degree days from start to Average maximum soil Average maximum air timing end of stress period temperature temperature leaf stage leaf stage leaf early stage leaf latestage leaf stage Table 4. Length of stress treatments and precipitation during stress treatments, Malheur Experiment Station, Oregon State University, Ontario, OR. Water stress Length of stress Length of time soil water Precipitation timing tension above 4 kpa days hours inches 2-leaf stage leaf stage leaf early stage leaflatestage leaf stage

100 INSECTICIDE TRIALS FOR ONION THRIPS (THRIPS TABACI) CONTROL-25 Lynn Jensen Maiheur County Extension Service Oregon State University Ontario, OR Introduction Growers continue to seek answers about how to control thrips in onions. The 25 growing season had unusually high thrips populations that were difficult to control. The iris yellow spot virus, which is transmitted by thrips, also had a significant impact on bulb size and yield. This trial examined the efficacy of old and new insecticide chemistries on thrips control. Carzol and Success were two materials that showed promise in suppressing both thrips and the iris yellow spot virus while improving yields over currently registered products. Materials and Methods A block of onion 42 ft wide by 5 ft in length was planted to onion (cv. Vaquero; Nunhems; Parma, ID) on March 1, 25. The onions were planted as two double rows on a 44-inch bed. The double rows were spaced 2 inches apart. The seeding rate was 137, seeds/acre. Lorsban 1 5G was applied in a 6-inch band over each double row at planting at a rate of 3.7 az/i, ft of row for onion maggot control. Water was applied by furrow irrigation. The plots were 7.3 ft wide (2 beds) by 3 ft long and were replicated 4 times. Thrips counts were made by counting the total number of thrips on 15 plants in each plot. Treatments were applied (Table 1) and thrips counts were made weekly during the growing season (Table 2). Insecticide applications were made with a CO2-pressurized plot sprayer with four TeeJet 84 flat fan nozzles spaced 19 inches apart. All treatments were made with water as a carrier at 6 gal/acre and a pressure of 9 psi. There were 2 treatments as outlined in Table 2. Acephate is an older insecticide that is now manufactured by several companies. Carzol is an old product used mostly in the tree fruit industry. Stylet oil is specialty oil designed to control aphids by affecting their ability to feed. Admire is one of the new neonicotinoid insecticides that are effective for insect control in many other crops. Diatect is a natural pyrethrum that other production areas have reported to be effective on thrips. Acephate, Carzol, and Admire are not currently registered for use on onions. 9

101 Results and Discussion Thrips populations started relatively low, and then increased dramatically through mid- July (Fig. 1). By mid-july the average number of thrips per plant was near 9. The high thrips population caused a lot of foliar damage as well as infecting the crop with the iris yellow spot virus. Table 2 shows the weekly thrips populations and season average. There were significant differences in thrips populations at each sampling date. The four Carzol rates (8., 1., 16. and 2. oz), Aza-Direct + Success (with or without Stylet) and Success (1 oz) + Stylet all gave acceptable thrips control. The two highest rates of Carzol gave the best overall control. The Carzol treatments are illustrated in Figure 2 and the Success treatments in Figure 3. The standard insecticide treatment included Warrior and Lannate or MSR combinations. The late June and early July applications were effective for the standard treatment but control was poor after that. Carzol was particularly effective when applied in July. Admire was not effective when applied as a foliar spray. Diatect was applied during the first part of the season but results were poor, so a standard insecticide plus Prey Am treatment was initiated after July 18. Acephate was very effective in 24 trials, but was only moderately effective in 25. The iris yellow spot virus infected the onions in the trial around mid-july. Two evaluations of iris yellow spot virus severity were made, one on August 3 and again on August 23 (Table 3). When the average thrips population and the August 3 disease severity (ratings) are graphed together it is clear that virus disease severity is related to thrips populations (Fig. 4). About 7 percent of the iris yellow spot disease can be explained by thrips populations. Yield is shown in Table 4. There were significant differences in all size categories except jumbo. The three highest rates of Carzol gave the highest overall yield and the highest yield of colossal and supercolossal bulbs. The treatments with Success were next highest. There is a strong correlation between total yield and thrips population (Fig. 5). The relationship between iris yellow spot severity and total yield was not as strong as for thrips populations and total yield (Fig. 6). The standard insecticide treatment was not significantly better than the untreated check. Aza-Direct when rotated every other week with a combination of Warrior plus MSR was poor at controlling thrips, which was also reflected in the yield. Conclusion The two highest Carzol treatments gave excellent thrips control and produced the highest yields. Applications of Success were also beneficial in reducing thrips populations and increasing yield compared to the untreated check and the standard insecticide treatment. The standard insecticide treatment was not significantly better than the untreated check. If Carzol becomes registered for use on onions, based on this year's efficacy data, a treatment program might consist of early applications of the 91

102 standard program, followed by an early and late July application of Carzol. Both Carzol and Lannate are in the carbamate insecticide class, and because there is already resistance to Lannate, care should be taken with Carzol use, should it be registered. Table 1. Application data for the onion thrips efficacy trial, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. Application date Temperature F Relative humidity % Wind MPH Application time 6/ :3 5:3 pm 6/ : am 2:3 pm 6/ : 7: pm 6/ :3 am 1: pm 7/ :3Oam 1:OOpm 7/ : 11: am 7/ :3Oam 12:3Opm 7/ : 11:3 am 92

103 Table 2. Weekly thrips population and season average, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Treatment Rate/acre 14-Jun 2-Jun 27-Jun 5-Jul 11-Jul 18-Jul 26-Jul 2-Aug 6-Aug Average Thrips per plant Carzol 8.Ooz Carzol looz Carzol l6oz Carzol 2z Admire 16oz Admire 24oz Aza-Direct alternated with 8 oz Warrior + MSR* 3.8 oz + 2 pt Aza-Direct alternated with 16 oz Warrior + MSR* 3.8 oz + 2 pt Untreated check Standardt Standardt + Stylett Aza-Direct + Success + 16 oz + 1 oz Aza-Direct+ Success l6oz+looz Success + 1 oz Success + 6 oz Standardt 2.4 lbs Standardt (early season) Success (late season) 1 oz 2.4 lbs Success alternated with Admire 1 oz + 16 oz Acephate* 8oz *Rotated on weekly basis. tstandard = Warrior plus either Lannate (3. pt) or MSR (2. pt). *Stylet oil applied at 1 percent v/v. discontinued due to lack of control. (.5) Least Significant Difference at alpha =.5.

104 Table 3. Iris yellow spot virus subjective rating in thrips trials, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Treatment Rate/acre 3-Aug 23-Aug virus rating* Carzol Carzol Ca rzol Carzol Admire Admire Aza-Direct alternated with Warrior + MSRt Aza-Direct alternated with Warrior + MSRt Untreated check Standards Standards Aza-Direct + Success 8. oz 1 oz 16 oz 2 oz 16 oz 24 oz 8 oz 3.8 oz + 2 pt 16 oz 3.8 oz + 2 pt l6oz+looz Aza-Direct + Success Success + Success + + (early season) + Success (late season) Success alternated with Admire Acephatet LSD (.5) 16 oz + 1 oz 1 oz 6 oz 2.4 lbs 1 oz 2.4 lbs 1 oz + 16 oz 8 oz * = healthy, 5 = most foliage dead. trotated on weekly basis. = Warrior plus either Lannate (3. pt) or MSR (2. pt). oil applied at 1 percent v/v. discontinued due to lack of control

105 Table 4. Yield of onions treated with different insecticides to control thrips, Malheur Experiment Station, Oregon State University, Ontario, OR, 25. Treatment Rate/acre Colossal Colossal Super- Total Mediums Jumbo + supercwt/acre colossal yield colossal cwt/acre Carzol 8.Ooz Carzol looz Carzol l6oz Carzol 2z Admire l6oz Admire 24oz Aza-Direct alternated with 8 oz Warrior + MSR* 3.8 oz + 2 pt Aza-Direct alternated with 16 oz Warrior + MSR* 3.8 oz + 2 pt Untreated check Standardt Standard Aza-Direct + Success + 16 oz + 1 oz Aza-Direct + Success 16 oz + 1 oz Success + 1 oz Success + 6 oz Standardt 2.4 lb Standardt (early season) Success (late season) 1 oz 2.4 lb Success alternated with 1 oz + 16 oz Adm ire* Acephate 8oz LSD (.5) 42 NS wrotated on weekly basis. tstandard = Warrior plus either Lannate (3. pt) or MSR (2. pt). *Stylet oil applied at 1 percent v/v. discontinued due to lack of control.

106 Figure 1. Season-long thrips populations (untreated) on onions in an insecticide efficacy trial, Maiheur Experiment Station, Oregon State University, Ontario, OR, 25. U) I- 'I (') \rv Cd' Carzol 8 oz Carzol 1 oz _*_Car-zoIl6 oz 2 oz * Untreated Check Figure 2. Efficacy of insecticide for thrips control on onion, Maiheur Experiment Station, Oregon State University, Ontario, OR,

107 a 12 I ID / / Untreated Check Standard A AzaDirect Success + Stylet AzaDirect + Success Success + Stylet (1 oz) Success + Stylet (6 oz) Figure 3. Success combinations compared to standard insecticides and the untreated check for thrips control in onions, Malheur Experiment Station, Oregon State University, Ontario, OR, R2 = I D U) -1 C U) U) U) U) c i C,) rj (_) B C, D D Co a U) B ) Thrips Disease Figure 4. Average thrips populations compared to iris yellow spot virus severity in onions with different insecticide treatments, Maiheur Experiment Station, Oregon State University, Ontario, OR,

108 a) ci) COO) 1 + JcweAes aseaskj ASAI c A2a Direct. (82) rotate Var MSR UTO Diatect fib) Standard (earlg) + Success (late) Standard + Stylet > a- x G)a) Aza Direct (82) rotate War MSR OW Diatect (1 lb) a) =C UTC Standard (early) Success (late) a) Standard A2a Direct (16 2) rotate Var + MSR Diatect + Standard Success (1 2) rotate Admire (16 2) Admire (24 2) Acephate (82) Admire (16 2) Success (62) + Stqlet Car2oI 182) A2a Success Stglet Success (1 2) + Stglet Success Carzol [16 2) Carzol (1 2) Car2ol (2 2) ca) E Qa)G co a- ) -c )) a) CO-i-' 5-CO a-c EU) CE ) Ace phate (8 2) Admire (16 2) coo) ca- Ox Success (62) + Stglet >5- Standard + St!Jlet Standard A2a Direct (16 2) rotate War + MSR Diatect + Standard Success (1 2) rotate Admire (16 Admire (24 2) Car2oI (82) 2) A2a Success + Stglet Success (1 oz) + Stylet A2a + Success Car2ol (16 2) Car2ol (1 2) Car2oI (2 2) - CO > D co c '-,-s pp'.& J3B11M3 PP!A 1e41 E Loc!) C)

109 A THREE-YEAR STUDY ON VARIETAL RESPONSE TO AN ALTERNATIVE APPROACH FOR CONTROLLING ONION THRIPS (THRIPS TABACI) IN SPANISH ONIONS Lynn Jensen Malheur County Extension Service Clinton C. Shock and Lamont D. Saunders Malheur Experiment Station Oregon State University Ontario, OR Introduction Onion (A ilium cepa L.) is a major economic crop in the Treasure Valley of eastern Oregon and western Idaho. Annually about 2, acres of onion are grown in the valley. Typically, Spanish hybrids are grown for their large size, high yield, and mild flavor. The principal onion pest in this region is onion thrips (Thrips tabaci, Lindeman). Thrips cause yield reduction by feeding on the epidermal cells of the plant. Onion thrips can reduce total yields from 4 to 27 percent, depending on the onion variety, but can reduce yields of the largest sized bulbs from 27 to 73 percent. The larger sized colossal and supercolossal bulbs (greater than 4 inches and 4.25 inches, respectively) are difficult to grow and demand a premium in the marketplace. Growers typically spray three to six times per season to control onion thrips. Treatments include the use of synthetic pyrethroid, organophosphate, and carbamate insecticides. The ability of these products to control thrips has decreased from over 9 percent control in 1995 to less than 4 percent control in 25. Onion growers are applying insecticides more frequently in order to keep thrips populations low. New biological insecticides with low toxicity to beneficial predators have been developed, including neem tree (Azadirachta indica A. Juss.) extracts (azadirachtin) and bacterial fermentation products (spinosad). Both of these materials have previously been evaluated for thrips control and have performed poorly compared to conventional insecticides. However, studies during the past 3 years have shown that season-longapplications of spinosad and azadirachtin are superior to conventional insecticide programs for controlling onion thrips. Materials and Methods A 1.5-acre field was planted to the onion varieties 'Vacquero' (Nunhems, Parma, ID) and 'Redwing' (Bejo Seeds, Oceano, CA) in a split-plot design on March 14, 23, March 23, 24, and March 21, 25. Vaquero is a yellow variety and Redwing is a red variety. Red varieties are generally assumed to be more attractive to thrips than yellow 99

110 varieties. The onion varieties were planted as two double rows on a 44-inch bed. The double rows were spaced 2 inches apart. The seeding rate was 137, seeds/acre. Lorsban 15G was applied in a 6-inch band over each row at planting at a rate of 3.7 ozil, ft of row for onion maggot control. Water was applied by furrow irrigation. The field was divided into plots 37 ft wide by 1 ft long. There were three treatments with six replications. The three treatments were a grower standard treatment, an untreated check, and the alternative treatment. The grower standard treatment included Warrior (lambdacyhalothrin), MSR (oxydemeton-methyl), and Lannate (methomyl). The untreated check did not receive any treatments for thrips control. The alternative treatment included Success (spinosad) and (azadirachtin). Insecticide treatments were applied 7-1 days apart during the growing season (Table 1). All insecticides were sprayed in water at 31 gal/acre in 23 and 39 gal/acre in 24 and 25. Thrips populations were sampled by two methods. The first was by visually counting the number of thrips on 2 plants. The second method was by cutting 1 plants at ground level and inserting the plants into a Berlese funnel. Turpentine used in the Berlese funnel dislodged the thrips from the plant, into a jar containing 9 percent isopropyl alcohol. The collected thrips and predators were then counted through a binocular microscope. Thrips populations were monitored weekly through the growing season. The predator populations were monitored using pitfall traps that contained ethylene glycol. They were evaluated three times per week. The Berlese funnel was also used to monitor predators foraging on the plants. The onions were harvested in September and graded in October of each year. Results and Discussion Weekly thrips populations are compared in Figure 1. The alternative program had a significantly lower average thrips population than the untreated check in all years (Fig. 2). Visual damage to the foliage was observed with the variety Vaquero in 24 and 25 but not in 23. The visual thrips damage to Redwing was greater than for Vaquero. There were no yield differences between any of the treatments with Vaquero in 23 but the alternative treatment had significantly more colossal- and supercolossal-sized bulbs in 24. In 25 the alternative program produced significantly fewer mediums and higher total yield than the untreated check. The alternative program gave significantly higher colossal and supercolossal yield compared to the untreated check (Table 2). Redwing had significantly more colossal-sized bulbs with the alternative treatment all years compared to both the standard or untreated check and a significantly higher total yield in 23 compared to the untreated check. In 25 the alternative program had 1

111 significantly higher yields than either the standard treatment or the untreated check (Table 3). Predator populations (Fig. 3) were significantly higher in the alternative and untreated check treatments than in the standard treatment. The predator population consisted mostly of spiders, big-eyed bugs, minute pirate bugs, damsel bugs, lacewings and lady bird beetles. The 24 and 25 seasons produced an epidemic of iris yellow spot virus (IYSV) in the trial area and surrounding fields. The IYSV is a new disease currently spreading to most production areas of the United States and the world. Onion thrips is the vector, so this trial gave the opportunity to evaluate the alternative program for IYSV control (Table 5). The onions grown under the alternative treatment were healthier and had significantly less virus than those under the standard insecticide treatment or the untreated check. Red onions often exhibit thrips scarring when placed in storage due to continued feeding by the insects. The alternative treatment produced significantly fewer damaged bulbs after storage compared to the untreated check for the Redwing variety. Conclusion The alternative treatments were equal to or in some cases significantly better than the standard insecticide program. There was a general trend towards higher yields in the larger bulb classes, which give a higher return to the grower. The alternative program gave better thrips control, reduced foliage damage and increased beneficial insect populations, perhaps by allowing the beneficials to forage on thrips. The alternative program produced less thrips damage to red onions in storage and reduced the incidence of iris yellow spot virus. References Jensen, L., B. Simko, C. Shock, and L. Saunders. 23a. Alternative methods for controlling thrips. British Crop Protection Council: Crop Science and Technology 23 Congress Proceedings. 2: Jensen, L., B. Simko, C. Shock, and L. Saunders. 22. Alternative methods for controlling onion thrips (Thrips tabaci) in Spanish onions. Pages in Proceedings of the 22 Allium Research National Conference. Jensen, L., B. Simko, C. Shock, and L. Saunders. 23b. Alternative methods for controlling onion thrips (Thrips tabaci) in Spanish onions. Proceedings of the 23 Idaho-Malheur County Onion Growers Annual Meeting. 7pp. 11

112 Jensen, L., C. Shock, B. Simko, and L. Saunders. 23c. Straw mulch and insecticide to control onion thrips (Thrips tabaci) in dry bulb onions. Pages 19-3 in Proceedings of the Pacific Northwest Vegetable Association Seventeenth Annual Meeting. Table 1. Application dates of insecticide treatments for thrips control in onions, Malheur Experiment Station, Oregon State University, Ontario, OR, Application date Treatment* Application date Treatment Application date Treatment June 7 A, D June 6 B, D June 7 A, D June14 D June16 B, D June15 B, D June 25 C June 23 C, D June 22 C, D July 3 D July 1 C, D June 29 B, D July7 B July8 B, D July8 C, D July11 D July19 C, D July22 B, D July 25 C July 29 C, D August 1 C, D July29 D *Treatments Rate Amount/acre A: Warrior B: Warrior MSR 3.84 oz 3.84 oz 2. pt C: Warrior Lannate 3.84 oz 3. pt D: Success 1. oz Aza-Direct 2. oz 12

113 Table 2. Yield and grade of Vacquero onion with different strategies for controlling onion thrips, Maiheur Experiment Station, Oregon State University, Ontario, OR, Super- Total Treatment Medium Jumbo Colossal colossal yield cwtlacre Untreated check Standard* Alternativet LSD(.5)t ns ns ns ns ns 24 Super Total Treatment Medium Jumbo Colossal colossal yield cwtlacre Untreated check Standard Alternative LSD(.5) ns ns ns 25 Super Total Treatment Medium Jumbo Colossal colossal yield cwt/acre Untreated check Standard Alternative LSD(.5) ns 96. *The grower standard treatment included Warrior, MSR, and Lannate. tlhe alternative treatment included Success and Asa-Direct. significant difference at alpha = 5 13

114 Table 3. Yield and grade of Redwing onion with different strategies for controlling onion thrips, Malheur Experiment Station, Oregon State University, Ontario, OR. 23 Super- Treatment Medium Jumbo Colossal colossal Total yield cwtlacre Untreated check Standard* Alternativet LSD(.5) ns ns 62.2 ns Super- Treatment Medium Jumbo Colossal colossal Total yield cwt/acre Untreated check Standard Alternative LSD(.5) ns ns 16.5 ns ns 25 Super- Treatment Medium Jumbo Colossal colossal Total yield cwt/acre Untreated check Standard Alternative LSD(.5) ns ns 7.4 *The grower standard treatment included Warrior, MSR, and Lannate. tthe alternative treatment included Success and Asa-Direct. 14

115 Table 4. Average iris yellow spot virus (IYSV) injury among insecticide treatments, Maiheur Experiment Station, Oregon State University, Ontario, OR, Treatment lysv* 24 IYSv* 25 Untreated check Standard Alternative LSD (.5).4.6 *Scale: dead, 5 = healthy, no lesions. Table 5. Thrips injury on stored Redwing red onion, Maiheur Experiment Station, Oregon State University, Ontario, OR, 23. Treatment Thrips injury* Redwing Alternative 1 Standard 1.3 Untreated check 1.5 LSD (.5).3 *Scale: = no injury, 1 = severe injury. 15

116 U) I- 4-. th > Jun 24-Jun 3-Jun 9-Jul 23-Jul 31-Jul 7-Aug 14-Aug fr- Alternative -- Standard fr- Untreated C 12 1 U) 8 -c.1-i th > Jun 15-Jun22-Jun29-Jun 6-Jul 13-Jul 2-Jul 27-Jul 3-Aug 1-Aug - Alternative. - Standard a-- Untreated C I- c 8 > Jun 16-Jun 23-Jun 3-Jun 7-Jul 14-Jul 21-Jul - Alternative --- Standard *- Untreated 28-Jul 4-Aug Figure 1. Thrips population response to an alternative thrips control program on onions, Malheur Experiment Station, Oregon State University, Ontario, OR,

117 23 _ Avg. thrips I plant Untreated Standard Alternative 24 U) I- th Untreated Standard Alternative j. 4 > 3 1 Untreated Standard Alternative Figure 2. Average season-long thrips populations on onions in an alternative thrips control program. Columns with the same letter are not significantly different, Maiheur Experiment Station, Oregon State University, Ontario, OR.

118 4-. U) I- 4-. U) I. th Untreated Standard Alternative Figure 3. Predator populations in the alternative thrips control trial in onions, Malheur Experiment Station, Oregon State University, Ontario, OR,