Pacific Northwest growers are vigilant following reports of spotted wing drosophila among Concord grapes in eastern Washington and the early appearance of the flies in traps in British Columbia’s Okanagan Valley in Canada.
While the susceptibility of wine grapes is not known, table grape and stone fruit growers fear the tiny fly could be a devastating new pest for the region.
The fly, native to Asia, was originally identified in strawberry fields around Watsonville, California, in August 2008. It was discovered in Pinot Noir grapes in the upper Willamette Valley of Oregon last year as well as in a noncommercial wine grape vineyard south of Abbotsford in British Columbia’s Fraser Valley. It has since been identified in the Okanagan Valley, where trapping suggests some flies may have successfully overwintered.
Drosophila suzukii, as the pest is known scientifically, is distinct from D. melanogaster on account of its predilection for healthy, mature fruit rather than damaged or rotting fruit. Thin-skinned fruits such as berries (including wild blackberries), cherries, and grapes are particularly vulnerable. Some peach growers in the Willamette Valley reported losses of up to 80 percent last year.
Both tree fruit growers and grape growers are concerned because a fruit fly infestation makes fruit unsightly to fresh-market consumers and raises the risk of spoilage. While the fly isn’t a threat to human health, no one wants damaged fruit.
“This is unacceptable,” Mark Bolda, a farm advisor specializing in strawberries and caneberries at the University of California, told growers attending the Pacific Agriculture Show in Abbotsford earlier this year.
Unfortunately, he said, there are no simple solutions for controlling the pest.GF-120 NF Naturalyte fruit fly bait provides effective short-term control, while long-term results can be had with stronger substances such as malathion and Delegate (spinetoram). But if the fruit is ready to pick, chemical controls may not be possible.
Organic management is equally difficult.
Bolda recommends bagging and removing cull fruit, though he knows it’s labor intensive.
“I realize this is not a popular option,” he said. “