Effect of pesticides on integrated mite management in Washington State

The effect of pesticides used against codling moth, Cydia pomonella L., on integrated mite management was studied for three years in five or six commercial apple orchards in central Washington. Phytophagous and predatory mites were counted throughout the season in blocks ranging from 0.4-1.6 ha in size treated with four codling moth insecticides. In one year of the study (2006), five out of six orchards experienced elevated mite densities relative to the standard. In four orchards, novaluron caused a 3.0-16.9× increase in mite populations; acetamiprid caused a 2.6-3.4× increase, and thiacloprid caused a 1.7-13.8× increase. In the fifth orchard, the organophosphate standard had an extremely high mite population, in addition to all three experimental treatments. In 2005 and 2007, only one or two orchards had elevated mite levels in the novaluron, acetamiprid, and thiacloprid treatments. Additive effects of codling moth and thinning programs were evaluated in small plot research trials. Treatments with all three elements [1) codling moth insecticide; 2) calcium polysulfide; 3) carbaryl] produced the highest levels ofspider mites. Three sulfur-containing products (calcium polysulfide, ammonium thiosulfate, and dry flowable sulfur) were evaluated for their effect onGalandromus occidentalis (Nesbitt) and apple rust mite, Aculus schlechtendali (Nalepa). All three materials caused suppressed G. occidentalis numbers. Calcium polysulfide caused the greatest reduction in apple rust mite numbers, ammonium thiosulfate the least reduction, with dry flowable sulfur intermediate between the two. Additive effects of codling moth materials, carbaryl, and sulfur-containing products may be causing increased mite levels in Washington orchards