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SWD threat eased up this year


Monitoring program didn’t produce large numbers until late in the growing season.


By Judie Steeves I


t was quite a different year for the newest pest of soft fruits, Spotted Wing Drosophila, with little damage until the season was almost over, reports berry specialist for the agriculture ministry, Mark Sweeney. SWD is a vinegar fly that infests ripe, soft-skinned fruit such as blueberries, raspberries and strawberries, rendering it unfit for market.


It’s native to Asia and was first discovered in the Pacific Northwest in 2008. By the next year it had grown so rapidly whole crops had to be abandoned and in 2010 it was discovered infesting crops in both the Fraser and Okanagan valleys. “We spent a lot of energy getting the word out early in the season to the thousand berry growers in the valley, because we’d had crop losses the previous year, but this turned out to be a good year,” Sweeney commented.


An aggressive program of pest control was advised by the ministry to protect berry crops and because buyers, both manufacturers and retailers, were aware of SWD, it was critical to provide clean fruit to the market, he said.


However, “We put the traps out early and we waited and waited and waited and the weather never really heated up until September.” “We got through most of the raspberry season without any intervention. There weren’t enough degree-days to allow it to develop,” he said.


Sweeney said from trapping activities last winter, it’s believed that few survive the winter. By March the traps weren’t catching any more of the tiny flies, even though earlier in the winter they had been catching some.


Then, they need enough food to build up a couple of generations


British Columbia Berry Grower • Winter 2011-12 15


high in fall because they are just feeding. Perhaps they go through a behaviour shift, said Sweeney.


Despite the name, wings of male Spotted Wing Drosophila have spots, but females (above) do not. As with males, the dark bands at the edge of each abdominal segment are unbroken when viewed from above.


before they become much of a threat to crops.


However, by October, there were phenomenal numbers being caught in the traps, but Sweeney said they wonder if the flies are still


reproductive at that point or whether they’re just feeding.


“We couldn’t find any in fruit in mid-October,” he noted. Ministry entomologist Tracy Huppelscheuser in Abbotsford is heading up an investigation into whether they are still reproducing or whether the numbers in traps are


There’s also a question about what bait what should be used in traps, and whether that should vary through the season, for maximum attraction. At any rate, the good news is that growers did get through the year with little damage, although later blueberries experienced some infestations.


“The longer the fruit hangs the more chance


there is of an infestation. Any tree or bush-ripened fruit is susceptible, and machine-picked fruit hangs longer, so there is more of an issue with it,” he noted.


Over the winter, there will be an exchange of information with colleagues to the south and discussions about how best to approach control of the pest next year in local fields, said Sweeney. Growers should attend the SWD information sessions at the Pacific Agricultural Fair Jan. 26 to 28 for up to date reports.


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