WALNUT HUSK FLY CONTROL WITH REDUCED RISK INSECTICIDES

Walnut husk fly (WHF), Rhagoletis completa Cresson, is a serious insect pest of walnuts in California. Control of WHF relies on repeated applications of broad-spectrum insecticides combined with a feeding stimulant to suppress adult flies before oviposition. The broad-spectrum insecticides suppress beneficial insects and mites that in turn suppress a number of secondary insect and mite pests. Thus an efficacious and environmentally benign WHF control needs to be developed to reduce or eliminate broad-spectrum insecticides. To this end, laboratory and field studies were conducted from 2002 to 2005 to evaluate spinosad as a replacement for broad-spectrum insecticides. In laboratory trials, spinosad at low rates was not as efficacious as malathion but was as efficacious as esfenvalerate and superior to pyrethrin. WHF mortality as a result of feeding on GF-120 was adversely affected by increased WHF density. The longevity of GF-120 appears to be very short under hot and dry California conditions. In field trials, GF-120 and Success 2SC provided significantly lower infestation as compared to the blank bait check and was equivalent to the grower standard of malathion or chlorpyrifos.