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Hot Summer Lowers SWD Pressure 

After last winter’s harsh conditions, hopes were that the spotted wing drosophila pressure would be low this past summer.

As it turns out, spotted wing drosophila pressure was low. It wasn’t the harsh winter that affected the pest, however. By early June, SWD numbers were similar to most years, according to Oregon State University Extension entomologist Vaughn Walton. It was the hot summer.

“I think that the dry weather, the hot temperatures made a huge difference,” Walton said in late September. “That played in our favor.”

Despite the low pressure, Walton said most growers he talked with maintained regular treatment schedules. “They did not want to take a chance, and I credit them for that. I think growers have learned that this is not something to take lightly. One week you’ll have no eggs in the berries. The next week it will be five. The next week it will be 50. It can change very, very rapidly,” he said.

“The big problem with these bugs is that they’ve got a tremendous reproductive potential. So even if they are knocked out during winter, you need to still worry about them and deal with them in the season, because the populations can explode very quickly. And even in mid-summer, where we had nice warm, dry weather, if it cools down for a short period, the pressure will just go back up. So one can never really fully rely on the heat or the dry weather.”

Asked what it will take to knock down populations in the winter, Walton said freezes, and several of them.

“You definitely need deep freezes and the more deep freezes you have the better. And dry is never bad,” he said. “You want dry weather in winter, which we didn’t have this past year.”

Researchers Making Progress in Battle Against SWD 

Oregon State University Horticulture Department entomologist Vaughn Walton said he and OSU horticulturist Clive Kaiser are working on two new products – both non-pesticides – that could help blueberry growers control the spotted wing drosophila (SWD).

One, a protectant, has resulted in an average of 60 percent reduction in egg-laying. The second, an attractant, could be used as a bait spray and is also cutting egg-laying dramatically in replicated research trials.

Walton couldn’t share all results because the compounds used in the products are proprietary, but said he believes the products could be valuable for growers hoping to reduce pesticide treatments.

The first product, a full-cover spray, protects against egg laying. “They just can’t get through the protectant,” Walton said. He added that the product is specially formulated for blueberries, so berries don’t lose their blush.

The second product works by forming liquid beads on blueberry plants that attract flies. The product contains a non-pesticide toxin that is lethal to flies but harmless to humans.

“We are basically looking at manipulating the behavior of the bugs,” he said.

“We are making progress,” Walton said in regard to the eight years scientists have been researching the pest. “Finally, we are making progress. I’d say in the next ten years, we will drop our pesticide use by at least fifty percent. If you look at these two products, and I’m sure there will be others as well, and then parasitoids, instead of spraying on average five sprays a year, we will be at two or three maybe, just during the ripening period.”

Walton said researchers still are waiting for permits to advance studies into use of parasitoids to help in SWD control. “The permit process is taking longer than what we expected. Luckily, we’ve got a few other things going on, as well,” he said.

Walton also this past summer found that utilizing drip irrigation as compared to overhead resulted in significantly less egg laying.

“We had more than double the number of eggs laid in overhead irrigation as opposed to drip,” Walton said. “These flies don’t do very well in dry conditions.”



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