Fruit flies infesting state’s raspberries

“We have a large raspberry patch - a beautiful one that people love,’’ said Linda Hoffman, who runs Old Frog Pond Farm, an organic farm that grows raspberries and apples in Harvard. “And it is closed. It is so sad. We closed the whole patch.’’

The fruit fly, called the spotted wing drosophila, is an invasive pest from Asia that first showed up on the West Coast in 2008 and has rapidly spread across the country. It tends to infest soft fruits, such as berries and grapes.

The fly appears to have arrived early this month in Massachusetts - which, according to the state Department of Agricultural Resources, ranks 10th nationally in raspberry cultivation.

The timing, shortly after Tropical Storm Irene, caused some farmers to wonder whether it hitched a ride on the storm. But an entomologist who has been on the lookout for the fly - he calls it “SWD’’ - said it was already well on its way, marching up the East Coast after being found in North Carolina, New Jersey, and Pennsylvania earlier.

“This critter is something we’ve been watching for,’’ said Alan Eaton, extension specialist in entomology at the University of New Hampshire Cooperative Extension, who said the fly’s presence was confirmed in New Hampshire Sept. 6. Eaton said this fly is particularly aggressive: The fruit flies most people are accustomed to infest fruit that is overripe, needing cracks or rot spots to get going. The female SWD, in contrast, can lay its eggs underneath the skin of the fruit, infesting it earlier.

Growers and specialists stressed that people should not be alarmed; the pest is harmless to people. It can, however, ruin a crop, causing fruit to rot more quickly. Several farmers said they were devising interventions, such as removing overripe fruit and spraying, to get rid of the pest, so that they could reopen their raspberry patches soon.

At Silferleaf Farm, an organic farm in Concord with two acres of raspberries, Tom Johnson said that the problem surfaced about a week after the hurricane - just as he was breathing a sigh of relief that the farm successfully weathered the storm. Initially, he said he thought the plants were just bouncing back from the heavy rains, since they are sensitive to moisture. But the fruit seemed to be rotting too fast, and he eventually realized that it was an entirely new kind of fruit fly.

“These guys will go for even underripe [fruit], and they look a little bit different - they have devilish red eyes,’’ Johnson said. “And the males have a black spot on their wings.’’

Johnson sent an e-mail to customers Friday saying that picking was suspended but said he had seen tremendous support from the local community. Some came to pick anyway, not caring that berries were damaged, and he received a large order for a sweet raspberry vinegar that can still be made. He said he has been setting traps to catch the flies and is hoping cooler weather will help.

Jim Mussoni, a private pest control consultant who works with farmers throughout Massachusetts, said he has been setting traps in many counties to get a handle on the problem.

Farmers are eyeing their options, many of which will add time and expense to the harvest.

Nathan Nourse, co-owner of Nourse Farms in Whately, said the farm has established new practices: keeping to a very tight schedule of picking, using crop protectants to prevent infestation, and no longer discarding bad berries on the ground, where they would provide an easy reservoir for the flies to lay their eggs.

Already, farmers are looking to next year, worrying about whether the insects will survive the winter and present problems to a wider range of crops.

“We’ve hoped it wasn’t going to get here . . . and then it did,’’ Nourse said.

Carolyn Y. Johnson can be reached at cjohnson@globe.com. Follow her on Twitter @globecarolynyj.