Invasive fly species threatens berry crop

ADDISON COUNTY — Berry growers across New England are on high alert for a new invasive insect species this year.
“We’ve been hearing all about it for the last few years,” said Jon Satz, whose Wood’s Market Garden in Brandon sells berries, along with many other vegetables, herbs and flowers.
The spotted wing drosphila, a smaller relative of the common fruit fly, has multiplied dramatically across the country in the last five years. First detected in California in 2008, it spread to the southeastern U.S. by the following year. It was first detected in New England in late 2011 after Hurricane Irene, though it stayed in the southern regions. Blueberries and raspberries are particularly vulnerable, according to UVM Extension berry specialist Vern Grubinger.
“We know what the susceptible crops are based on experiences in other parts of the country,” he said.
Last year, UVM researchers and local growers learned about the pest firsthand.
“In 2012, it was in most of New England,” he said.
But the pest’s reach into northern Vermont and the Champlain Valley last year was spotty. That was at least partially because some of the crops that are most susceptible, like late-season blueberries and fall raspberries, are not as common because of early frost.
“I would say almost everyone who did fall raspberries got it, but raspberries are not a big part of your typical northern New England farm,” Grubinger said.
Nonetheless, the Champlain Valley was not immune. Grubinger remembered that berry growers at the Intervale in Burlington were especially hard-hit last summer.
This year, he expects that the fly will be “everywhere.”
Unlike its close relation the fruit fly — which lays its eggs in overripe, nearly rotting fruit — the female spotted wing drosphila has a razor-sharp egg-laying limb that can penetrate newly ripe berries, particularly late in the season when the fly’s numbers get larger. Interestingly, the harm isn’t done by the eggs or larvae, which are so miniscule that they are hard to see.
“You can’t see it,” Grubinger said. “People called up last year and said, ‘What’s this disease eating all my blueberries?’ They didn’t know it was an insect.”
Nor should anyone be too worried about accidentally consuming a berry that the fly has already reached.
“It sounds gross, but there’s no harm to humans from eating them,” Grubinger said.
The danger to the fruit is, in fact, the tiny hole the female makes to lay her eggs, which exposes the inside of the fruit to external bacteria, causing them to rot very quickly. A single female can lay hundreds of eggs.
Grubinger and UVM Extension, in collaboration with growers in areas like Connecticut and Rhode Island — where the pest has been for a couple of years — are researching ways to minimize the impact in Vermont. Grubinger said many have found that simply harvesting berries as soon as they are ripe does a lot of good.
“Clean picking is the way to go,” he said.
He and others have also experimented with inventing traps for the insects, which will stop and eat sugar the moment they sense it.
“Someone figured out that if you put two gallons of sugar in 10 gallons of insecticide, they’ll eat it,” he recalled.
The idea is to devise a trap that the flies will go to before the fruit, and that will kill them before they can leave again. The science has not yet caught up, but a number of effective spray-free techniques have been developed already, and Grubinger is sure the chemicals that attract flies and the poisons that kill them will become increasingly refined.
In the meantime, a set of instructions for Grubinger’s latest low-cost, do-it-yourself design — which attracts the flies with a mix of sugar, yeast and apple cider vinegar, then drowns them in a mix of wine, vinegar and detergent — is available on his website, www.uvm.edu/vtvegandberry/SWDInfo.html.
“If you have 50 traps and 100 berry plants, (the traps) make a difference,” he said.
The most thoroughly effective and environmentally sound option known so far is netting, with openings no bigger than one square millimeter. The netting can be costly, however, and difficult to find. Grubinger knows of one place that sells it in bulk, but the seller is located in Quebec.
For Jill Kopel, the co-owner of New Leaf Organics in Bristol, which offers pick-your-own berries as well as vegetables, the netting would have been her first choice but the cost made her hesitate.
“We had already made a couple of big capital investments on the farm this year,” she said.
Kopel said she had been “very aware” of the threat posed by the invasive fly, and had attended several workshops during the winter months to learn how to make her farm less vulnerable.
“We are trying to very proactive,” she said.
Kopel said that she and her husband had considered expanding their berry operations this year, but had decided not to in large part because it seemed like too costly an investment when area growers were still unsure of how devastating the new fly would be.
Down in Brandon, Satz considers himself lucky that he mostly has June-bearing berries, and has also put expansion plans on hold.
“I just personally wouldn’t want to spray berries close to consumption,” he said. “We’re certified organic, and it’s an awfully tough pest. It is making me think twice about expanding my raspberry crop.”

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