Good Fruit Grower

March 15

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P ear psylla is a serious foe in Pacific Northwest orchards, accounting for more than half of a pear grower's pest management expenses and about 20 percent of total nonfixed operating costs. If not properly controlled, the pest can also downgrade fruit. Honeydew that the nymphs produce drips onto fruit and serves as a medium for growth of sooty mold. It can sometimes be bad enough that it reduces photosynthesis significantly and makes the pear unsalable, Dr. Tom Unruh, geneticist, with the U.S. Department of Agriculture in Yakima, Washington, said at the North Central Washington Pear Day in January. "Honeydew is the bane of a grower's life." Pear psylla has two distinct adult forms: a winter form that overwinters and a summer form that develops from eggs laid in the spring. Winterform adults are bright green when they first molt from the nymphal stage and then turn darker. Their wings have a smoky patch. The sum- merform adults also are blue at molt, but turn more of a yellow color and have clear wings. They are smaller than the winterforms and less fecund. Each fall, about 80 percent of the winterforms leave orchards for overwintering sites, sometimes feeding on apples or other deciduous fruits as they disperse. They are able to survive the winter on a wide range of plants, but do not reproduce on the other hosts. They can be active during warm days in the winter, and they can feed from plants to get water, but do not mate or cause damage. Winterforms become much more active when the weather starts to warm up and the days become longer. In mid to late February, they begin returning to orchards to feed and mate. "That's when you start thinking about dormant sprays—about the time you start seeing some green show up on the ground of the orchard," Unruh said. When they return to orchards in the spring, they identify pear trees by a waxy coating on the branches, using receptors in their feet as well as their mouths. By March, they start laying eggs on the base of fruit buds with oviposition increasing through bud swell and leafout. By bloom, eggs are still abundant and small nymphs are evident. The abundance of psylla in the spring can vary greatly, and the way to keep them in check is to target the winterforms before they start laying eggs, Unruh said. The overwintering psylla are much more susceptible to insecticides in the spring than they were in the fall, as they use up their fat body to sustain themselves while not feeding during the winter. Unruh warned that psylla populations increase more rapidly on trees with high nitro- gen levels and lots of suckers. "Pear psylla is a nitrogen junky, and maybe some of our growers are, too," he said. "It's clear from work done here in Washington and other countries that your pear psylla abundance increases when there's a lot of nitrogen." It's not uncommon to see pear trees with three- to seven-foot-tall shoots growing up from the top, and those are breeding grounds for psylla, he said, suggesting that a plant growth regulator, such as Apogee (prohexadione calcium), might be used to limit that upright growth. Monitoring The easiest way to sample for pear psylla adults is with beating trays, Unruh said. Returning adults are not attracted to colored traps, though summerforms do respond to yellow traps. Scientist Dr. Cristelle Guédot, formerly with the USDA in Yakima, dis- covered that pear psylla has a pheromone that attracts males and could be used for monitoring. Unruh said there is ongoing research by Dr. David Horton and colleagues with the USDA to discover the potential for combining the pheromone with a toxicant as an attract-and-kill form of control. 38 MARCH 15, 2014 GOOD FRUIT GROWER Avoid the Orchard of No Return NORTHWEST, WA: Tim Purcell..........Mobile 360-630-4285 EASTERN WASHINGTON: Robert Rauert ....Mobile 509-728-2004 EASTERN WASHINGTON: Jason Rainer .......Mobile 509-731-5424 THE DALLES & HOOD RIVER, OR: David Sbur ..........Mobile 971-563-8848 Telone® II, Telone C-17, and Telone C-35 are registered trademarks of Dow AgroSciences LLC. Telone II, Telone C-17, Telone C-35, and Pic-Clor 60 are restricted-use pesticides. • Row and broadcast applications available • Specializing in tree fruit, hops, grape, berry, and nursery crops Soil Fumigation Specialists Serving the Northwest for 30 years Replant disease can take the profit out of any orchard. Soil fumigation services offered by Trident manage replant disease and other soil-borne pathogens. Trident offers custom applications of Telone® C17, Telone C35, and Pic-Clor 60. Control psylla EARLY Returning winterforms are more susceptible to pesticides than they were in the fall. by Geraldine Warner "Pear psylla is a nitrogen junky, and maybe some of our growers are, too." —Dr. Tom Unruh PHOTO BY ELIZABETH BEERS, WSU Early instar pear psylla nymph and eggs

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