Good Fruit Grower

March 1

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14 MARCH 1, 2016 Good Fruit Grower A n opportunistic pest known to cause extensive damage in California and the eastern United States has arrived in Oregon's cherry orchards in the wake of a harsh freeze during November 2014, and growers are advised to be on the lookout for it. The American plum borer has been setting up shop in trees weakened by the historic cold snap that saw temperatures dip to minus 12°F in some places in Oregon's Columbia River Gorge. "I think it's just going to be a pest to watch for," said Drew Hubbard, a research and devel- opment specialist for G.S. Long in The Dalles, Oregon. Hubbard and researchers call the plum borer, a moth whose larvae feed on the cambium under the bark, "opportunistic." They are attracted to compromised trees, perhaps with injuries or places of soft tissue. After the freeze, growers pruned way back to the leaders, sometimes to the trunks, to encourage their trees to start all over again building their structure. The "succulent" new growth attracted the borers, Hubbard said. In early August last year, growers and fi eld representatives noticed new shoots becoming frail and falling off trees. They also found plum borer larvae and their frass, or droppings, and caught up to 20 adult moths per trap per week toward the end of that month in low-lying pock- ets where temperatures dipped the most. Hubbard collected samples of the larvae and asked Dr. Peter Shearer, an entomologist with Oregon State University Mid-Columbia Agricultural Research and Extension Center in Hood River, to identify them. The plum borer, a native to North America, has little history in the Northwest, Shearer said. "This insect is a major pest elsewhere (Michigan, California, New York) but has never been a big problem here," Shearer said in an emailed statement. Local integrated pest management guides don't mention it. Growers and fi eld representatives found small populations in 2010 after a lesser freeze, while Dr. Elizabeth Beers, an entomologist at Wash- ington State University's Tree Fruit Research and Extension Center in Wenatchee, spotted them attacking graft unions two recent years in Washington — in 2013 in Malaga and in August 2015 in East Wenatchee. Borers make THEIR MARK Northwest growers advised to watch for American plum borer. by Ross Courtney Pest Management PHOTOS COURTESY DR. DAVID BIDDINGER/PENNSYLVANIA STATE UNIVERSITY Long-lasting insecticides on bark wounds are effective for control of American plum borer. The pest, more common in Michigan and California than in the Northwest, has been causing some damage to cherry trees in The Dalles, Oregon, apparently attracted to trees damaged by a November 2014 freeze. The moth larvae have a unique purple-like color. Larvae overwinter in white, fuzzy cocoons under the bark.

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