Spotted Wing Drosophila Descends On Golden State

Just as entomologists have been warning West Coast growers all winter, Spotted Wing Drosophila (SWD) is starting to damage small fruits, especially California cherries. Bill Coates, a University of California Cooperative Extension tree fruit and nut farm advisor in several coastal counties in and around Monterey, eMailed Monday that he had about 40 commercial calls in the past month about SWD from either growers or pest control advisers.

“We are just beginning to see damage now on early-ripening pollinizers such as Black Tartarian,” Coates wrote in an eMail to GrowingProduce.com, adding that the full extent of the threat in cherries won’t be seen for a few weeks. “Our Bing harvest is in early to mid-June.”

SWD gained prominence one year ago when it started hitting berries and then cherries in California. It then moved up the coast, and by late summer it was attacking blueberries and other berry crops in Oregon and Washington. The pest is something of a mystery, as entomologists don’t know if it just arrived in the U.S. a year or two ago, or if it just wasn’t doing much damage in the past.

SWD is believed to be originally from Japan, according to Mark Bolda, a University of California Cooperative Extension farm adviser in Santa Cruz County, who specializes in strawberries and caneberries. Bolda spent much of January reviewing the Japanese literature with the help of translators, but has found few answers. He does know one thing, though: This is one serious pest, and the Pacific Coast climate is perfect no matter what the crop. “If you’re on the coast growing fruit, period, you need to be aware,” he says.

In the immediate future, Coates is concerned about California’s crazy weather this spring, in which normal warm days in the 70s have often been followed by cold wet days in the 60s. The forecast for the next few days is not a bright one for cherry growers, he notes.

“Rain is expected over the next week and any cracked cherries will provide additional breeding sites for SWD since they will not even need to puncture the skin to lay eggs,” Coates eMailed.

It’s not that growers have been caught unprepared, he emphasized. Many of the growers in the region have attended the meetings they have held on SWD, including the last two in February and one in January as well as those last year. Information has also been included in the last three issues of his “Tree Topics” newsletter. Most growers are fully aware of this pest and associated control measures.

Coates added that quite a number of calls have been to identify either male or female SWD in traps. On the Central Coast, many growers have applied two or three pre-harvest insecticide sprays and some will end up with four. “We do not know at this point whether sprays will be needed during harvest to protect the second half of the harvest period,” he wrote.

There is also a lot of activity among avid home gardeners about the problem through the local chapters of the California Rare Fruit Growers, Coates noted. Asked if he’d heard from many home hobby growers, as other extension agents have reported, Coates responded: “The average home gardener will not be calling me until after they have an infestation, much like what occurred last year when SWD hit urban San Jose home gardens. This pest will be very difficult to control in home gardens with a limited choice of control materials, inadequate spray equipment and a general lack of knowledge.”

For home gardeners, Coates says he and his colleagues have summarized their guidelines at the web site: http://www.ipm.ucdavis.edu/EXOTIC/drosophila.html.
Their commercial cherry grower guidelines are at the website: http://www.ipm.ucdavis.edu/PDF/MISC/2010_Cherry_Spotted_Wing_Drosophila.pdf.