Good Fruit Grower

April 15

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40 APRIL 15, 2014 GOOD FRUIT GROWER I t's exactly a hundred years since Washington State College entomologist Dr. Alex Leonard Melander proposed the then-novel concept that insects could develop resistance to pesticides. "It was the fi rst time that anyone had brought up the idea that insects could be resistant to sprays," Dr. Elizabeth Beers, Washington State University entomologist, reported during the North Central Washington Pear Day in January. Pesticides had only recently been invented, and it was assumed that if a pesticide worked at that time, it would work forever, she said. But Melander suspected that San Jose scale had become resistant to lime sulfur sprays. The tree fruit industry and scientists have been grappling with resistance ever since. Soon after joining WSU in 1985, Beers chaired a panel discussion at the Washington State Horticultural Association's annual meeting on how to address resistance of mites. "Apparently, nothing has changed since 1985," Beers said, warning that spider mites are acquiring resistance to a current product called FujiMite. "We're moving to the point where FujiMite will not be effective at the full rate." In 1985, the concern was resistance to Plictran (cyhexatin) and Vendex (fenbutatin-oxide), which were in a class of miciti- des known as organotins. When they fi rst became available they were very effective, but as time went on, they became less and less effective. The panelists at the hort meeting proposed three ways to respond to this: 1. Use a higher rate or apply more often. 2. If an acaricide doesn't work, combine it with another in the hope that the two together will do a better job. For example, PREVENTION is BEST strategy Mites can soon develop resistance to overused miticides. by Geraldine Warner PHOTOS COURTESY OF ELIZABETH BEERS Two-spotted spider mites are a mere sixtieth of an inch long but are a big concern for pear growers.

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