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No damage yet from spotted wing drosophila

Earlier this summer, there was concern that the latest threat to fruit orchards and berry farms in California — the spotted wing drosophila (SWD) — might harm grapes.

Once called the cherry vinegar fly, the insect has become established in 21 counties in the state. It attacks fruit, including cherries, raspberries and strawberries, just as it softens before harvest. SWD earlier caused extensive damage to California sweet cherries and raspberries.

So far, though, it doesn’t appear to be causing much of a problem in wine grapes.

“We haven’t seen any indications that SWD will damage vineyards as it has cherry orchards,” says Paul Verdegaal, University of California Cooperative Extension (UCCE) farm advisor for San Joaquin County.

“At this point, we know it’s out there, and it has been found in a couple of wine grape vineyards in the county this season. But the harvest only recently got under way, so we’re not sure what, if any, problems SWD will cause.”

Roger Duncan, UCCE farm advisor for neighboring Stanislaus County, says he’s received no reports of SWD damage to wine grapes in his county. Nor has Rhonda Smith, UCCE viticulture farm advisor for Sonoma County.

In August, Larry Bettiga UCCE viticulture farm advisor for Monterey, San Benito and Santa Cruz counties, did get one report of SWD being trapped in a Santa Clara county wine grape vineyard, although no grapes were damaged by the insect.

“The traps were on the edge of the vineyard next to a cherry orchard,” he says. “We assume SWD flew in from that orchard.”

The majority of Central Coast wine grapes are grown in areas where there are no cherry orchards to attract SWD, he says. There, wine grape producers have adopted a wait-and-see approach as to whether the insect actually moves into the vineyards.

“The grapes are now ripe,” Bettiga says. “So, if the pest is attracted to them, the traps should be picking up some from now through the rest of the season. The bulk of the harvest is still to come.”

Should control prove necessary, some of the insecticides used on cherries to control SWD are also registered for use on grapes, he notes.

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