SWD Numbers Up in 2016; Stink Bugs Down

With growers practicing good spotted wing control, determining population fluctuations from year to year can be difficult, said Oregon State University entomologist Vaughn Walton.

That said, Walton said he expects population models will show higher levels of spotted wing in Oregon fruit crops this year than last, particularly because most believe last year’s high temperatures reduced the pest’s population.

Still, Walton said, with good control practices, growers have generally avoided large-scale damage from the pest.

“If you’ve got pesticides and you are spraying them correctly, you are never going to have much of an issue,” Walton said. “If you are not spraying them correctly, then you are in trouble.”

Walton added, “From what I’ve seen, growers have done well.”

Walton said that it helps that in Oregon it generally doesn’t rain in the summer, like it does in some other blueberry production regions, such as Michigan. And the fact that only limited cherry production takes place in the Willamette Valley also provides a benefit for blueberry growers.

“In Europe, to the best of my understanding, they have a mix of cherries, blueberries and other fruit all being produced in the same production area,” he said. “And they had early rains and cherry cracking this year and that totally messed things up. It shot the spotted wing numbers through the roof and they just had endless issues in some of these production areas, because they don’t have the pesticides we do.

“With us, I think we’ve got the space and we’ve got the climate,” Walton said. “We aren’t producing cherries in large numbers here and we didn’t have the rains when the crops ripened. That really plays in our favor.”

Walton also noted that brown marmorated stink bug numbers were down this year.

“We had seen this gradual increase in 2013 and 2014,” he said. “We saw a slight drop off in 2015 and this year it is definitely lower.”

Oregon State University Extension entomologist Nik Wiman said he has heard reports about damage to fruit crops from the stink bug, but not berry crops.

“There are a few growers that sustain some damage every year,” Wiman said, “and that is just because of their location. They just have a big population around them.

“It probably has to do with the surrounding vegetation and the plants that are there for them to feed on,” he said. Wiman added that once the pest gets established in an area, it is difficult to lower their numbers.

The best opportunity often occurs in the winter, he said. “You can make somewhat of a dent in their population by managing those overwintering populations,” he said. “In some cases, you will see aggregations of high densities of bugs on certain buildings or in certain areas of buildings. In those cases, if you can vacuum them up or kill them by treating them, that can make a difference.”

Wiman noted an Asian parasitoid is reducing brown marmorated population in Portland, but he doesn’t believe it is having much of an impact outside of the Portland metro area.

He and Walton suspect climatic conditions are the big driver in the fluctuations of brown marmorated stink bug populations.

“For some reason, there was more mortality in the overwintering population (this past year),” he said. “I don’t know if because the winter was relatively warm, they just burned through their nutritional reserves faster or what, but we had a lot higher mortality and that got them off to a slow start.”