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Invasive Asian fruit fly returns, decimates raspberry harvest

SHOREHAM — As if an usually wet start to the summer and the threat of early frost weren’t enough, Vermont’s raspberry crop has another foe to contend with — an invasive species from Asia that has crept its way into the state.
Bob Douglas of Douglas Orchards in Shoreham said his raspberry crop has suffered the last two years.
“We started nice, and then got decimated by the spotted wing drosophila,” said Douglas, who stopped selling his berries weeks ago because the fly had damaged the crop so badly.
The spotted wing drosophila, or SWD, is a native species of Japan. It was found in California in 2008, and made its way east to New England by 2011. Last year the pest was found in Vermont, according to Vern Grubinger, a vegetable and berry specialist with the University of Vermont Extension.
The SWD is from the same genus as the common fruit fly. The main difference between the two species is while the fruit fly can lay eggs only in rotting fruit, the SWD can lay eggs in firm, ripening fruit. Female SWD have a saw-like appendage used for laying eggs that enables them to deposit eggs into the flesh of fruit.
Fruits with thinner skins, such as raspberries, seem to be more susceptible to the SWD, according to Grubinger. Apple and pear crops have not been affected.
The peak season for SWD in Vermont is late summer to early fall.
Lately, the effects of the SWD are being felt across Addison County.
“We had a good summer raspberry crop overall, but the fall crop has been slim,” said Laura Borys of Champlain Orchards in Shoreham. Borys said the raspberries have suffered from a SWD infestation.
“It doesn’t rot the berries, they just get soft and mushy if you don’t eat them within a few days,” Borys said.
Douglas said farmhands sprayed his raspberry crop with an organic pesticide every week this summer, but the flies began showing up at the end of August. By the first week in September, the crop had been completely destroyed. 
“They’re garbage, and we can’t sell them,” Douglas said.
Last year, the orchard did not know about the SWD and was caught by surprise. Eighty percent of that crop was lost. Even with spraying this year, 75 percent of the crop was lost.
Douglas said he will try different approaches next year, including the possibility of using different sprays and spraying more thoroughly. This year, spraying was inconsistent because of heavy rains.
Grubinger said it is important to harvest fruit as soon as it is ripe, this can lessen the damage the SWD can do. After harvest, fruit should immediately be placed in the fridge or freezer to slow the decomposition process.
Covering plants in netting with openings less than one millimeter is another effective way to keep the fly away.
As SWD are attracted to alcohol, yeast and vinegar, simple traps can be made with plastic beverage cups to capture adult flies, Grubinger said.
But even with these precautions, there is no guarantee plants will be free from SWD infestation.

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