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Organic Controls for Walnut Husk Fly Developed

The Issue

In the Central Coast, walnut husk fly has been a major roadblock to converting conventional walnut orchards to organic production. (Gross returns are as much as 50% higher for organic walnuts.) Husk fly damage can approach 100% in unsprayed orchards but no effective organic controls have previously been available. Other pests such as walnut blight and codling moth already have adequate organic controls.

What Has ANR Done?

Two new management tools for the control of walnut husk fly have been developed by San Benito County Farm Advisor Bill Coates and UC Berkeley Extension Specialist Bob Van Steenwyk. Surround (kaolin) is a clay-based material that is sprayed on trees, turning them white. Besides providing walnut husk fly control, it may also reduce sunburn and induce earlier harvest. It is currently registered as an organic material. Spinosad is a microbial by-product that acts as an insecticide and has provided excellent walnut husk fly control when mixed with a bait. It has received organic registration for use on the husk fly in a fruit-fly bait, and organic registration as a separate insecticide is expected.

Testing of organically-acceptable materials by UCCE began in the Central Coast in the mid-1990's in response to local industry requests. Tests showed that available insecticides and other control techniques such as mass-trapping were ineffective. In 2000, the first tests of spinosad were conducted in San Benito County. In 2001, expanded tests showed excellent control of husk fly when spinosad was combined with a bait. Further tests were conducted in 2002 in other locations. The researchers worked with Dow AgroSciences to pursue organic registration for spinosad.

In 2001, the first tests utilizing Surround were conducted in San Benito County. An extensive test in 2002 showed efficacy if spray coverage was adequate. Surround is already registered as organically acceptable treatment. Results of both research projects were presented to the industry at local meetings and in the Walnut Research Reports published by the Walnut Marketing Board.

The Payoff

More Local Growers Finding Organic Walnut Production Feasible

More walnut growers in California's Central Coast already have or are planning to convert to organic production because organic walnut husk fly controls developed by UCCE are available. Walnut growers in the Central Coast have a competitive advantage because of very high quality and less codling moth damage than many other growing regions in California. However, they suffer from lower yields and higher land and production costs compared to the Central Valley. Conversion to organic production helps to maintain a walnut industry in an area that has been increasingly converted to houses or row crops.

Although walnut production already is a relatively "clean" agricultural industry, reduced impacts on the environment such as less ground water contamination by nitrates and pesticides, reduced pesticide runoff to the Monterey Bay Marine Sanctuary, and increased farm worker safety also are potential benefits of conversion to organic production.


Supporting Unit: San Benito County

Bill Coates, Farm Advisor, UC Cooperative Extension, P. O. Box 1956, Hollister, CA 95024-1956
831-637-5346(PH), 831-637-7111(FAX), bwwcoates@ucdavis.edu