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Spotted Wing Drosophila Update
by OSU entomologist Vaughn Walton and John Schmitz

Spotted Wing Drosophila (SWD), the first Oregon infestations of which were recorded in August 2009 at a U-pick farm in Benton County, is becoming an increasing problem in blueberry fields.

Today it’s estimated that the insect has found its way into all major blueberry production areas in Oregon.

As Oregon State University horticultural entomologist Vaughn Walton puts it: “This pest is causing losses, specifically in later maturing varieties if you do not monitor for it.” He goes on to add that, “It will not be possible to eradicate it. It is too widespread and even if specific growers manage it well, it will continue to invade those areas.”

The good news is that Walton and others at OSU have developed a website that tells growers all about SWD and how to monitor and treat for it.
That web address is: swd@hort.oregonstate.edu. “It’s a very, very widely used website. We’ve gotten more than 100,000 hits already,” Walton said.
The website presents the results of a statewide monitoring program that shows where SWD outbreaks have occurred in Oregon. “But, of course, growers have to go out and check for themselves and see if they have a problem,” Walton said.

Monitoring, the methodology for which is covered at the site, is a rather detailed process. (“It is quite an effort. You have to monitor at least weekly,” Walton said.) The site also lists the various registered insecticides that can be used in both conventional and organic fields, as well as application rates.
When there is no treatment, SWD can “very easily” claim up to 40 percent of a crop, Walton said. Once SWD has been discovered, it’s usually too late to treat for it, he added.

Unlike other destructive pests that overwinter in huge numbers, only about one percent of drosophila adults survive the winter, Walton said. However, that little colony soon builds back to the original numbers as more and more fruit becomes infected.

Another bit of good news, for the most part, is that blueberries aren’t as badly affected by SWD as other fruit crops, Walton said. The exception to that is the very late maturing varieties.

Fruit damage occurs when adult females lay their eggs in the fruit and larvae commence to eat the fruit.

Walton said that when monitoring, growers need to make sure to put traps not only around the edges of fields but also in surrounding areas where other fruit, especially wild blackberries, grows.

Oregon Blueberry Commission • P.O. Box 3366 • Salem, Oregon 97302
Paid for by the Oregon Blueberry Commission, an agency of the State of Oregon.