Commercial fruit growers in Manitoba welcome all visitors, but the one no one wants to see this summer is spotted wing drosophila (SWD).
The tiny vinegar fruit fly was first detected in 2013 in Manitoba but that year — and in 2014 — showed up in early August after most fruit crops were already harvested.
Last year it showed up at the beginning of July and multiplied so quickly by mid-month it had heavily damaged many commercially and homegrown fruit crops across the province.
“(Last year) it started coming in near the U.S. border the first week of July,” said provincial fruit crops specialist Anthony Mintenko. “By mid-July it was starting to be in every raspberry field moving north and it was all spread across southern Manitoba.”
This year the Manitoba Agriculture Crop Industry Branch’s Fruit Crops Program has stepped up its monitoring, with detection traps set out last week in areas where the invasive fly has been traditionally detected. These include the Red River Valley, the South Pembina Valley, and south-central and southeastern regions of Manitoba.
“It’s a canary in a coal mine sort of thing,” said Mintenko, who was setting out traps at a cherry farm just outside Carman last week.
“If we do spot it and our fruit crops are at risk we’ll let growers know and what steps they need to take to help prevent infestation,” he said.
The Fruit Crops Program is developing an SWD fact sheet with more information for growers — including instructions for how to set up one’s own detection traps — and expects to post it on Manitoba Agriculture’s website under Current Crop Topics this week.
Early detection is critical, Mintenko said. Found early enough there are several approved insecticides such as Malathion, Success, Entrust, Mako, and Delegate that will provide effective control of SWD, he said.
But growers must use these insecticides in rotation, however.
“It is important to constantly rotate every application through different insecticide chemical groups to avoid potential insecticide-resistance issues with SWD.”
The new invasive fruit fly is of East Asian origin. It was first detected in the Pacific region of the U.S. in 2008 and is now well established across North America. It was detected in Ontario in 2010. It causes heavy damage to mature fruit crops by piercing healthy fruit and laying its eggs inside.
Researchers say it is unlikely SWD is overwintering here. Rather, they suspect it is being blown in on wind currents, Mintenko said.
It’s when field conditions are just right for its reproduction — as they were last year — that it will multiply rapidly.
“Last year it was very warm and very moist. Field conditions, especially in raspberries, weren’t drying out and it was in the low 20s C to mid-20s C. Perfect conditions for reproductive growth (of SWD). Populations just exploded,” he said.
Both commercially and homegrown crops in many parts of Manitoba were hard hit. Wayne and Edith Smith, on whose Carman-area farm Mintenko was setting detection traps last week, lost more than half their raspberries and basically their entire cherry crop to SWD in 2015. The Smiths have one of the province’s few large cherry orchards.
They’d opened it up for U-picking on July 18, only to have to shut it down before the week was out, Wayne said.
“We noticed it within three days of starting to pick,” he said, adding the first sign of it in their cherry crop was shrivelled fruit.
“It cut our income in half basically,” he said.