The Use of Straw Mulch to Enhance Predator Populations Along with Biopesticides to Control Onion Thrips in Dry Bulb Onions

2003 Annual Report for SW02-017

Project Type: Research and Education
Funds awarded in 2002: $73,800.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $10,750.00
Region: Western
State: Oregon
Principal Investigator:
Lynn Jensen
Oregon State University

The Use of Straw Mulch to Enhance Predator Populations Along with Biopesticides to Control Onion Thrips in Dry Bulb Onions


Onion thrips remain the main insect problem on onions produced in the Western United States. Tradional insecticides are no longer effective in some of the major onion production regions. This project has explored the option of using naturally occuring soft insecticides (or biopesticides) to supress thrips populations while allowing beneficial predators to keep the thrips population below economic levels. A high yielding, vigorous variety, Vacquero, has been tested for three years with excellent response to the program. One out of three years, yields with the biopesticides have significantly outyielded the commercial thrips control program and there has been a trend to increase yields in the other two years. This year two varieties that are moderately and extremely susceptible, respectively, were tested with similar results. The biopesticides have consistently yielded better than the commercial program.

Verbal and written reports have been given at several grower and scientific meetings.

Objectives/Performance Targets

1. Determine the relative effects of straw mulch, spinosad, and azadirachtin on thrips control, predator populations, and on yield and quality.
2. Demonstrate the effectiveness of the procedures on a larger scale in grower fields.
3. Conduct tours to familiarize and educate growers about project.
4. Educate growers on the advantages of alternative thrips control through presentations and publications.
5. Evaluate the financial impact of standard grower practices versus alternative control methods.


1. Demonstrated the effectiveness of spinosad and azadirachtin in allowing predators to control thrips on vigorous, high yielding varieties.
2. Demonstrated the effectiveness of spinsad and azadirachtin in allowing predators to control thrips on slow growing, thrips sensitive varieties such as Redwing and Flamenco.
3. Established that the alternative program is at least as effective as a commercial pesticide program and in most cases there is a yield and size increase.
4. Concluded that adding straw mulch for predator habitat is not necessary and does not increase the number of predators available for thrips control.
5. Conducted two grower tours of alternative practices for thrips control.
6. Presented alternative thrips control information to onion growers in the Idaho, Oregon, Washington and Utah production regions along with a written report of project.
7. Provided an economic analysis of the project to the Idaho/Malheur County onion growers. The alternative project netted approximately $200 per acre more than the traditional control program.

Impacts and Contributions/Outcomes

Impacts will be evaluated next year as growers adopt alternative methods for controlling onion thrips. Support for the project has been received from the Idaho/Eastern Oregon Onion Research Committee, the Malheur County Onion Growers Association and the Idaho Pesticide Commission.


Reid Saito

Malheur County Onion Growers Association
701 SW 5th Ave
Ontario, OR 97914
Clint Shock
OSU Malheur Experiment Station
595 Onion Ave
Ontario, OR 97914
Office Phone: 5418892174