Spotted Wing Drosophila an unwelcome visitor to fruit farms this summer

MAFRD began monitoring for SWD in 2013 and this is the worst year yet, say provincial fruit crops specialist

Altona-area fruit grower Waldo Thiessen knew what was wrong immediately when his U-pick customers started calling back a few hours after their first day in his raspberry patch in mid-July.

“They said they’d started to make jam, and, well, there was a lot of protein (in the raspberries),” he said.

It was larvae of spotted wing drosophila, and an “uh oh” discovery for the Thiessens, who promptly shut down their raspberry U-pick.
This isn’t the first time they’ve had this tiny fruit fly that lays its eggs in mature, healthy fruit crops show up, but it’s the earliest, said Thiessen, executive director of the Prairie Fruit Growers Association.

“We were not really looking for it at the beginning of July,” he said. “It kind of caught us flat-footed. We had a lot of damage.”

“We” isn’t just themselves either. Growers across Manitoba have been reporting the same unwelcome visitor.

Spotted wing drosophila (SWD) is a vinegar (fruit) fly of East Asian origin that can damage many crops by piercing healthy fruit and laying its eggs.

Early detection is critical because symptoms often do not appear until after the fruit is harvested.

Unlike the common fruit fly which feeds on overripe or rotting fruit, SWD will attack unripe to ripe fruit.

Unlike the common fruit fly which feeds on overripe or rotting fruit, SWD will attack unripe to ripe fruit.
photo: Bev Gerdeman, Washington State University

Manitoba Agriculture Food and Rural Development fruit crops specialist Anthony Mintenko said this is the worst year yet for SWD since MAFRD started monitoring for it in 2013.

In 2013 and again last year it showed up in early August after most fruit crops were already harvested. It was also reported only in south-central Manitoba in areas such as the Red River Valley and the Pembina Valley. This year SWD has been expanding northward and westward since the second week of July.

“This year it’s everywhere and it’s three to four weeks early,” said Mintenko.

“We’ve just kept finding it. Last week it started showing up in the Brandon area, far west as Elkhorn, far south as Deloraine and all the way through Glenboro. It’s shown up this week in Grunthal,” he said July 30.

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“It hasn’t shown up north of the city (Winnipeg) yet, but I suspect it will be there soon.”

The larvae of SWD are very tiny so growers’ reports of actually seeing them inside fruits such as strawberries and raspberries was surprising, he said.

“It definitely tipped us off that we had very very unusual event happening.”

Too late to spray

It’s hurt fruit producers who, not anticipating SWD would show up so early, didn’t detect it soon enough to spray for it. Mintenko said he estimates fruit crop losses from SWD could be anywhere from 25 to 50 per cent.

Unlike the common fruit fly which feeds on overripe or rotting fruit, SWD will attack unripe to ripe fruit, and most commonly affects fruits with thin skins such as raspberries, strawberries, blueberries, cherries and plums. It was first identified in Manitoba in commercial berry fields in early August 2013.

MAFRD entomologist John Gavloski said it’s not yet known whether this year’s insect infestation arrived in Manitoba from elsewhere or overwintered here.

“We don’t know much about their overwintering biology,” he said. “In the past we’ve gone on the assumption that they blew in or moved in, and up until this year they’ve come in later. There’s a possibility this is an overwintering batch.”

Fruit crops most at risk at this point, and which may require control measures are late season day-neutral strawberries and late summer-bearing raspberries, Mintenko said.

But if your fruit crop harvest is near completion, or you suspect what’s left is already infested, Mintenko is not advising producers to spray at this point in the year, he added.

The key is avoiding another year like this one in 2016 and that means being on watch for it earlier next year, he said. Growers can monitor for SWD using simple cider vinegar traps, and there are a number of insecticide options for producers to use if they’re detected next year.

MAFRD will continue its surveillance for SWD again next year.

“From here on in it’s going to be a matter of monitoring to determine when people maybe do need to start doing control practices.”

About the author

Reporter

Lorraine Stevenson

Lorraine Stevenson is a reporter and photographer for the Manitoba Co-operator with 25 years experience writing news and features. She was previously a reporter with the Farmers Independent Weekly and has also written for community newspapers in Winnipeg and Manitoba's Interlake.

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