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Drosophila pressure up this year, scientists warn


Capital Press

The spotted wing drosophila fruit fly could pose a greater threat to berry and cherry producers in Oregon and Washington this season, scientists are warning.

Populations were high last season and more flies likely made it through a mild winter, said Vaughn Walton, an Oregon State University Extension entomologist in Corvallis. Early blueberries and cane berries may be more susceptible this season, he said.

"A relatively warm spring enhanced their survivability and ability to lay eggs. Modeling shows there will be pressure, no question. Timing will be the key thing," Walton said.

Most growers know how to deal with it so it should not get out of hand, he said.

The Asian pest is alarming because it is the only one known to attack ripening fruits and berries, not just damaged and decaying fruit.

It was first detected in the U.S. in California strawberries in 2008. It moved into berries in the western parts of Oregon and Washington and into Central Washington cherries in 2010. It has been kept under control with early detection and pesticides.

Trap counts have been highest in Central Washington a month or more after cherry harvest. It has up to 13 generations a year. The greatest damage to cherry growers in 2012 was in the southern half of the state.

Eight of 17 regions in Central Washington caught their first flies by June 1 last year and 13 regions were at that level by May 29 this year, Elizabeth Beers, entomologist at the Washington State University Tree Fruit Research and Extension Center in Wenatchee, told Capital Press.

Flies were caught through the winter at a trap in Prosser, proving spotted wing drosophila winters over in adult form, Beers said.

A fly was found in an East Wenatchee trap May 16 and about the same time in Orondo and Quincy, she said. By May 22 flies were caught in Mattawa and from Sunnyside to the Tri-Cities, she said. The most recent have been Yakima, Oroville and Tonasket.

She said the only four regions where they haven't appeared yet this season are: Okanogan and Omak; Chelan and Manson; Rock Island and Malaga; and Union Gap and Zillah.

"Growers should anticipate a little more pressure this year," Beers said, noting it won't be a problem if they keep up with detection and pesticides.

A total of 61,722 spotted wing drosophila were trapped in Central Washington in 2012 up from 13,807 in 2011 and 60,381 in 2010, Beers said. She considers the 2011 season an anomaly because numbers were believe reduced by the pre-Thanksgiving Day freeze of 2010.


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