An Unwelcome Visitor

09/01/2009 02:00:00 AM
Vicky Boyd

The pest is not rated in Washington but is a general quality concern, says Brad White, Washington Department of Agriculture pest program manager in Olympia. The spotted wing was found in a residential property in Kings County and in a Washington State University raspberry plot in Pierce County.

“We’re not sure if it’s something that’s been around for a long time and someone just noticed it or whether it moved in recently,” White says. “Right now we’re in a wait-and-see mode.”

Flies target cherries

The pest caused significant damage to cherries this season from Gilroy, Calif., north to Sunnyvale, says Bill Coates, a UC Extension farm adviser in San Benito, Santa Cruz, Santa Clara and Monterey counties who specializes in tree fruits and nuts.

“It caused a lot of consternation and sorting of fruit,” he says. “In some cases, growers just quit harvesting. In San Benito County, we run a bit behind, so we had the added benefit of the knowledge and got started spraying early. It wasn’t nearly the pest down here.”

If it behaves like other drosophila fruit flies and has a short reproduction cycle, it will probably have 10 generations annually, Coates says. That could mean three generations during the period when cherries are susceptible.

The pest is native to Japan and China, which both have cold winters. So it’s a good guess that it will be able to survive California’s milder winters, Smith says.

The best detection methods

Because the pest is so new to the United States, researchers have hurried to try to answer some of the unknowns, such as the best monitoring methods and control techniques.

Bolda conducted a field trial this summer in a heavily infested raspberry block. He compared seven different lures or lure mixtures with a sweep net. The goal was to determine how to best trap for the pest.

Photo by Mark Bolda

Each of seven baits or bait mixtures were placed in a 500-milliliter Nalgene bottle with four 7/16-inch holes drilled into the lid and hung about 3 feet from the ground in the hedgerow.

Of the baits, methyl eugenol and a molasses mix captured no flies, Bolda wrote in a blog. GF-120 and a strawberry puree were most effective, capturing an average of nine flies in 24 hours.

The puree appeared more effective during the second trial as it was older and had begun to ferment.

But the sweep net provided the most effective way to evaluate fly numbers in the field, Bolda wrote.



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