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www.goodfruit.com GOOD FRUIT GROWER MARCH 1, 2014 35 694+ Acres Offered in 4 Parcels Parcels From 75± to 297+ Acres Vine Acres From 63± to 200± Acres to Be Sold at PUBLIC AUCTION Friday, April 4 th at 2PM Alderdale, WA 694± gross acres located within the Horse Heaven Hills Appellation with 335± planted to various wine grapes. e Horse Heaven Hills Appellation is home to 25% of Washington State's vineyard acreage and a source of the four 100-point Washington State Wines. 509.416.6060 mbauction.com Horse Heaven Hills AVA ©Shutterstock ©Shutterstock "Usually we find them on the underside of the leaf, residing along the leaf veins, especially the middle rib," she said. Often, you can see crawlers moving about. Other signs of spider mites are their webbing (which is why they're called spider mites) and cast skins from previous molts. Feeding by high populations of spider mites can cause speckling of leaves. "When populations are really high, you'll see yellowing and bronzing of leaves," she said, adding that leaves will begin to die due to the feeding behavior of mites. "Their piercing and sucking mouth parts suck out the cell contents." Severe infestations affect fruit quality by delaying fruit maturity and ripening due to a reduction of sugars. Natural enemies Spider mite integrated pest management strategies include biological control, using natural enemies like predatory mites and lacewing and ladybird beetle larva, cultural practices that minimize dust and manage vine- yard floor vegetation, and chemical control that uses targeted sprays. When using chemical control, there is always the problem of spider mites developing resistance from repeated exposure to the same chemical. "Two-spotted spider mites are one of the most resistant pests in the world and are resistant to more than 90 insecticides," she said. Piraneo believes that further understanding of mite resistance and toxicity could help improve mite management strategies. Resistance In studying resistance, she evaluated abamectin (Agri- Mek) and bifenazate (Acramite), common miticides used in Washington wine grapes. During 2013, Piraneo collected spider mite samples from leaves of 4 vineyards and 13 hop yards. Female spider mites were brought into the laboratory, transferred to leaf discs placed in petri dishes, and sprayed with labeled rates of the two prod- ucts. She measured toxicity by determining the percent of mortality within 24 hours of exposure and also deter- mined LC 50 values, the lethal concentration that kills 50 percent of the population. In hops, mortality rates to abamectin ranged from 100 percent mortality to 50 percent, indicating that some spider mite populations have developed resistance. For bifenazate, the lowest mortality was 76 percent. "Wine grapes did much better than hops, proba- bly because miticides haven't been used as much as in hops," she said, noting that miticides had not been used in the sampled vineyards in the past year. Mite populations from two of the sampled vineyards died in the petri dish before she exposed them to pesticides. The two remaining vineyard samples had 98 and 95 percent mortality. "The spider mite populations in the wine grapes were relatively susceptible to the pesticides," Piraneo said. She also studied spider mite populations in the lab to learn if they were capable of developing tolerance to the chemical within the same season. She found that in hops, two-spotted spider mite developed the largest increase in tolerance to abamectin, with the LC 50s increasing up to 107-fold after ten weekly sprays. A 14-fold increase in tolerance was observed with bifenazate. Spider mites developed tolerance by the tenth week of application of the same insecticide, but once sprays were stopped, tolerance decreased significantly. In grapes, two-spotted spider mite developed tol- erance to bifenazate, though not at the same rate as in hops. "High tolerances in spider mites on grapes have not been detected, but the pest has the capability to increase tolerance," she stated. She advises growers to monitor grapes frequently during the season, scouting for mites. "If you detect them early, you usually have time to react using control tac- tics," Piraneo said, adding that knowing what is present will lead to better management strategies. "But be aware that if you repeatedly use the same chemical for control, it can lead to resistance." • PHOTO COURTESY OF WASHINGTON STATE UNIVERSITY