Good Fruit Grower

March 1

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10 MARCH 1, 2015 GOOD FRUIT GROWER www.goodfruit.com T he shift from broad-spectrum organophosphates to new classes of pesticides that are more selective appears to have caused a shift in both pest and predatory mite species in Washington orchards. Rebecca Schmidt-Jeffris, graduate student at Washington State University in Wenatchee, found in recent studies that the little-known Amblydromella caudiglans was the predominant predatory mite in a significant number of apple orchard blocks she sampled. Dr. Stan Hoyt, retired entomologist at WSU, developed integrated mite management during the 1960s. He found that the predatory mite Typhlodromus occidentalis (later renamed Galendromus occidentalis) was resistant to the organophosphates widely used at the time to control codling moth. With judicious use of organophosphates, growers could conserve the "typhs," and avoid having to apply acaricides to control mites. Schmidt-Jeffris said the most common mite species at the time was McDaniel spider mite. Since then, there's been a grad- ual shift to other species, including two-spotted spider mite and rust mite. Recognizing that some of the new pesticide classes have nega- tive effects on natural enemies, Schmidt-Jeffris decided to sample 102 commercial apple blocks throughout Washington State. Leaf samples showed that while G. occidentalis was still by far the most predominant predatory mite, A. caudiglans dominated in 20 per- cent of the blocks. The species has been around for a long time, but recent changes in orchard management might have given it the opportunity to flourish, she said. PREDATORY mite comes to light While "typhs" still dominate in Washington, Amblydromella caudiglans is common in low-input orchards. by Geraldine Warner PHOTOS COURTESY OF WASHINGTON STATE UNIVERSITY Amblydromella caudiglans is the predominant predatory mite species in some Washington orchards. Pest Management

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