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An Organically Acceptable Seed Treatment Control for Seed Corn Maggot in Carrots

Carrot Country
Fall 2007

By Doug Walsh, Tim Waters and Sally O’Neal Coates
Washington State University Extension

Entrust™ is Dow Agrosciences’ organically certified formulation for its biological insecticide spinosad. Commercial pest control products containing spinosad in foliar spray or bait formulations have been developed and registered primarily to suppress pest insects from insect orders including Lepidoptera (caterpillars/worms) and Diptera (flies/maggots, mosquitoes). A group of entomologists with the New York State Agricultural Experiment Station began a course of research several years ago to test the feasibility of applying spinosad for maggot control on small-seeded vegetables in Northeast muck soils.

Their initial results looked promising, and their data was displayed at the USDA-Interregional Research Program No. 4 Food Use Workshop September 2006, in Indianapolis, Ind. After becoming aware of this research, we approached Mercer Canyons, one of Washington State’s major carrot producers, to inquire if this would be a pesticide that Washington carrot growers would use. The administration at Mercer Canyons readily agreed to participate in a trial, and our work commenced.

Seedcorn maggot, Delia platura, is an insect native to Europe. It was introduced to the United States in the early 1800s and has since colonized all arable regions on the North American continent. Seedcorn maggots feed on decaying organic matter and are known to infest the germinating seeds and roots of over 47 plant species. Beans, soybeans, corn and peas are the most seriously damaged hosts. To a lesser extent, crucifers, cereals, potato seed pieces, cucurbits, tobacco, onions, peppers, buckwheat and alfalfa are also injured by this pest. For carrot producers in the Pacific Northwest, entire circles have been destroyed by seedcorn maggot at considerable expense to carrot producers.

Conventional control in newly seeded carrot fields has been marginally achieved through the application of the organophosphate insecticide diazinon by ground application or by chemigation through center-pivot
irrigation systems.

Washington Trial
Carrot seeds, cv ‘Sugarsnax,’ were treated by Skagit Seed Services with Entrust at a rate of 50g active ingredient (spinosad) in March 2007. The seeds were planted on April 30, 2007, by a commercial planter in
replicated blocks at Sandpiper Ranch, near Paterson, Wash. The planting density was 3.8 pounds of seed or 1,102,000 seeds per acre. These plots were integrated into a carrot field planted with identical seeds that were not treated with Entrust. Diazinon was applied at 2.0 lb a.i. per acre by ground sprayer. The plots were replicated 16 times.

The plots were evaluated twice for seedling stand establishment. The first count was taken on May 24, 2007, and a second count was taken on June 8, 2007. Stand counts were taken by counting the number of seedling established in a double-ribbon row.

Treatment                          Seedlings per meter ±SE

*/ significantly more seedlings per meter in pair wise t-tests compared to the nontreated control at p<0.05

A tolerance for spinosad has been established on carrots, and a Section 3 pesticide registration has been established for foliar applications of Dow’s Spinosad insecticides Success™ and Entrust.

Representatives at Dow Agroscience have agreed to pursue 24C Special Local Need Registrations for their Entrust formulation for seed treatment on carrots. With due diligence, this registration will be submitted this winter and the treated seed product will potentially be available for growers to plant in spring 2008. This registration will go a long way towards helping carrot producers produce certifi ed organic carrots in the future.

Representatives at Dow Agroscience have agreed to pursue 24C Special Local Need Registrations for their Entrust formulation for seed treatment on carrots. With due diligence, this registration will be submitted this winter and the treated seed product will potentially be available for growers to plant in spring 2008. This registration will go a long way towards helping carrot producers produce certified organic carrots in the future.

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