Wheat straw used as a mulch on top of the onion bed has proved useful in reducing injury to thrips (onion and western flower) when used in conjunction with two “soft” insecticides. The insecticides are spinosad (Success – Dow Agra) and azadirachtin (Ecozin – AMVAC Co., and Aza Direct – Gowan Co). These active ingredients are registered for organic production. Four years of testing have shown this insect control program to be equal to or in most cases superior to conventional thrips treatments. Yield and size have been increased by the use of this program, and storage losses to red onions from thrips scarring is reduced.
Determine the relative effects of straw mulch, Success (spinosad), Ecozin (azadirachtin), and Messinger (harpin protein) on thrips control, predator populations, and on yield and quality. Three years duration.
Demonstrate the effectiveness of the procedures on a larger scale in grower fields.
Conduct tours to familiarize and educate growers about the project.
Educate growers on the advantages of alternative thrips control through presentations and publications.
Evaluate the financial impact of standard grower practices versus alternative control methods.
During the past three years alternative insecticides have demonstrated superior control of onion thrips when compared to conventional insecticides. Alternative insecticides in this trial are azadirachtin (Aza Direct and Ecozin) neem tree (Azadirachia indica, A Juss.) extracts and spinosad (Success), a bacterial fermentation product. Neither product has been particularly effective in short-term screening trials, but when applied throughout the season to plots with added straw mulch they have been very effective in controlling thrips and increasing yields. These insecticides are relatively safe to beneficial predators, thus allowing predator populations to increase while suppressing thrips populations.
A block of onion 36.7 ft wide by 600 ft long was planted in a split plot design to onion (cv. Vaquero, Flamenco, Sunseeds. Parma, ID; cv. Redwing, Bejo Seed Co.,Oceano, CA). 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 154,000 seeds per acre. Lorsban 15G was applied in a 6-inch band over each double row at planting at a rate of 3.7 oz/1,000 ft of row for onion maggot control. Water was applied by furrow irrigation. The plots were 40 ft wide by 100 ft long and were replicated six times.
Insecticide applications were made with a CO2 pressurized plot sprayer with four nozzles spaced 19 inches apart. All treatments were made with water as a carrier at 42.6 gal/acre. Thrips counts were made weekly through the growing season by counting the total number of thrips on twenty plants.
The onion bulbs were harvested by hand in September and graded in October.
Four years of trials have been accomplished in determining the efficacy of straw mulch, spinosad, and azadirachtin in controlling onion thrips. The harpin protein, Messinger, and the straw mulch did not add to the control of thrips and were discontinued from the program. Spinosad and azadirachtin were very effective in controlling onion and western flower thrips when used together in a complete management program. They were more effective in most years than the standard insecticide treatment programs.
The effects of this program have been demonstrated on small-plot research as well as on grower fields. Three years of research was needed to ensure that there was a high degree of probability that the program would work on a larger scale. One of the side benefits of this program is the suppression of iris yellow spot virus (ISY), a new disease of the U.S. onion industry. The 2004 and 2005 plots were infected with the virus, so an evaluation was made for ISY virus control.
Tours for growers and field personnel have been conducted each of the four years that the project has been in effect. Approximately 100 persons have been involved in each of the summer tours. The National Onion Association Summer Meeting agenda included the plots as part of their program. Other smaller tours for interested individuals have also been conducted.
Educational programs have been presented during the past four years to inform local growers of the benefits of the alternative thrips control program. In addition, the information has been shared in other onion-producing states such as Utah, Colorado, California, New York, and Washington.
The financial feasibility of the program has been evaluated. The alternative approach to thrips control costs about $200 more per acre than a conventional insecticide program but produces a net return of $300 per acre more than the conventional program, given normal onion prices.
The expected outcomes are:
Significantly reduce the amount of highly toxic pesticides used on onions.
Improve the yield and quality of onions grown in the western United States.
Improve the safety to pesticide applicators through the use of low toxicity bio-insecticides.
Reduce the impact of the new virus disease iris yellow spot.
Educational & Outreach Activities
Tours for growers and field personnel have been conducted each of the four years that the project has been in effect. Approximately 100 persons have been involved in each of the summer tours. The National Onion Association viewed the trial as part of the agenda for its summer meeting. Other smaller tours for interested individuals have also been conducted.
Educational programs have been presented during the past four years to inform local growers of the benefits of the alternative thrips control program. In addition, the information has been shared in other onion producing states such as Utah, Colorado, California, and Washington.
Written reports have been published in the OSU Malheur Experiment Station Annual Report and in the Idaho-Eastern Oregon Annual Meeting Report and distributed to all of the onion growers in Malheur County and Idaho. Written reports have also been distributed to growers in Utah, Washington, California, and Colorado.
The financial feasibility of the program has been evaluated. The alternative approach to thrips control costs about $200 more per acre than a conventional insecticide program but produces a net return of $300 more per acre than the conventional program, given normal onion prices.
An emergency section 18 for Success was applied for by the onion growers of Idaho and Oregon, but it came too late for them to adopt the program in 2004. A new section 18 was applied for in 2005 and a number of growers were able to utilize the program. Colossal sized bulb yields were increased along with net income, and iris yellow spot virus infection reduced by the growers who used the program.
Areas needing additional study
Iris yellow spot virus is an emerging disease problem in the United States. The disease is spread by onion thrips, and since the onion thrips is resistant to all of the commonly used insecticides, controlling thrips to control the disease does not appear to be an option except for the potential for the bio-insecticides to contol the disease. It has been found in most of the western production regions, plus in the vidalia region of Georgia. It can be devasting when environmental conditions are optimum. The virus infected the bio-insecticide plots in 2004 and 2005, and an evaluation of the impact of the different thrips treatment strategies and the control of iris yellow spot virus were conducted. Observations were that the bio-insecticides azadirachtin and spinosad were able to significantly reduce the effect of the iris yellow spot virus.
Additional work needs to be done to confirm this observation.