Issue link: http://read.dmtmag.com/i/263110
N ew research on spider mites did not find resistance to commonly used miticides in Washington State vineyards, but growers should not be lulled into thinking resistance won't develop. Spider mites are one of the largest and most destructive groups of pests in agriculture. They are commonly found in wine grape vine- yards, though are not typical in juice grapes. Of the five species most often found in wine grapes in the United States— Pacific, McDaniel, European red, two- spotted, and Willamette—the two-spotted spider mite, Tetranychus urticae, is the most common in eastern Washington wine grape vineyards. Washington State University graduate student Tara Piraneo studied spider mite control and resistance as part of her master's thesis, working with hops and wine grapes. "Generally, spider mites are considered a secondary pest, and it's only when a distur- bance to the environment occurs that we get concerned with populations," she said. "But when mites reach high populations, they can do real economic damage." In sharing her research with grape growers during the annual meeting of the Washington State Grape Society, Piraneo said that spider mites tend to be more serious in hot, dry years. Dust, cultivation practices, nitrogen application, and pesticides used to control other pests can all enhance spider mite populations. "Last year, with its warm temperatures and dry conditions, was a good year to study spider mites," said Piraneo, noting that spider mite populations are generally low in Washington vineyards but occasionally flare up. But with a short life cycle, spider mite populations can build rapidly. The spi- der mite life cycle is seven to eight days, and there can be multiple generations in a season. "After the crop is harvested, spider mites can overwinter as fertilized females or eggs and become a problem in the next season," she said. Detection Piraneo said it's important to scout and monitor vineyards so that mites can be detected early in the season before populations increase. Spider mites are small and difficult to see, but they are visible to the naked eye. A 10x lens can help with detection. 34 MARCH 1, 2014 GOOD FRUIT GROWER www.goodfruit.com Grapes Bronzing of grape leaves is a classic sign of spider mites. Spider mite resistance "My Grandparents made a living out of 10 acres of fruit and it's exciting to be able to help the Independent Grower not just survive but flourish. I have several years' experience in match- ing the right grower with the right customer at the right time! Please stop by and let's discuss what we can do for you!" Steve Black Sales Manager Meet our newest Matchmaker! s Over 20 years in the apple industry s Comes from a family representing over 100 years in the apple industry s 3rd generation apple guy! s Expertise in matching grower fruit with the perfect customer and Logistics Holtzinger Fruit Company welcomes Steve Black as New Sales Manager Contact Steve today and meet our new Matchmaker $IRECT s #ELL s -AIN BLACKS HOLTZINGERFRUITCOM A Growing Legacy Since 1816 Stark Bro's Nurseries & Orchards Co. 10#PYt-PVJTJBOB.0tt'BY Call 800-435-8733 now to ensure best selection. Many of the most popular varieties are still available. Are you ready? Are you Spring is coming ... ready? Spring is coming ... 4UBSL#SPT8IPMFTBMFDPN Two-spotted spider mite has the capability to develop tolerance to miticides in wine grapes. by Melissa Hansen