Invasive fruit fly threatens Minn. crops

An invasive fruit fly from Asia is attacking raspberry, blueberry and grape crops...at an alarming rate.

MONTROSE, Minn. -- An invasive fruit fly is threatening berry crops in Minnesota and forcing many growers to either change their techniques or get out of the business.

Spotted wing drosophila (SWD), native to Asia, was first detected in Minnesota in 2012. Unlike common fruit flies, which typically feed on overripe fruits, SWD causes damage when the female flies cut a slit and lay eggs in healthy fruit.

It primarily attacks raspberries, blackberries and blueberries but can also infest strawberries, grapes and stone fruit, according to the University of Minnesota Extension. 

"It's affected our raspberries, our strawberries, our grape tomatoes," said Paul Nelson with Untiedt's Vegetable Farm in Montrose.

Nelson said they spend more hours keeping their high tunnels clean--picking up berries that have naturally fallen to the ground--to help stop the spread of SWD. 

"Without spraying at all, your berries will become infected quite rapidly," Nelson said. "So as much as we don't like to spray, we do need to spray to control this pest."

Untiedt's also works with the University of Minnesota.

"They actually come out and do trapping for us on SWD ... giving us counts so we know when we need to spray," he said.

Bill Hutchison, a UMN professor of entomology and extension entomologist, calls the pest a game changer.

"One of the complicating factors is there's really no natural enemies that we can rely on," he said. "So growers, especially on short notice since this arrived in 2012, they've had to rely on insecticides to protect their berry crops--from wine grapes to raspberries, blueberries, blackberries, strawberries ... our small-fruit industry has definitely been impacted."

According to Hutchison, about 20 percent of the state's growers have either had to suspend berry production or have gone out of business because of SWD.

"So as these larvae develop within a berry, they're breaking down the sugars, the proteins in the fruit. And yes, eventually the fruit, the individual berries, turn to mush as the larvae are completing their development," Hutchison said.

UMN researchers have been working with a vineyard near Hastings on how to control SWD. This summer, they used exclusion netting on wine grapes.

"Exclusion netting is just a fine-mesh netting that's small enough to exclude SWD from getting in but it still allows... the climate to stay the same for the crop it's covering," said Dominique Ebbenga, a first-year master's student.

After reviewing some preliminary data, Ebbenga said, "We have some promising results showing that exclusion netting is excluding SWD."

Hutchison added, "It can literally completely eliminate the need for insecticides or greatly reduce it."

According to Hutchison, they plan on collecting a second year of data next summer.

You can find out more about SWD here.

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