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Okanagan Valley Grapegrowers Face the 64,000-Bug Question

January 2017
by Peter Mitham

Penticton, British Columbia—The invasive insect brown marmorated stink bug recently was found at a riparian site near Penticton in British Columbia’s southern Okanagan Valley.

Originally from Asia, the stink bug has become a leading cause of damage to tree fruits on the East Coast. Its detection in the Okanagan is the first in a major fruit-producing area of British Columbia, although there are signs that it may have become established in pockets of the province’s Lower Mainland. Vancouver is the country’s busiest port of entry, and several bugs have been intercepted on incoming shipments in recent years.

Betsy Beers, an entomology professor at Washington State University in Wenatchee, said the appearance of the pest in Penticton means it’s only a matter of time before it wings its way across the U.S.-Canadian border to Okanogan County, Wash. The bug has been identified in 17 counties in the state to date.

The good news for everyone, however, is that the pest takes years to become established in sufficient numbers that it can cause economic damage to agricultural crops.

“We have had no absolute, verified reports of damage in Eastern Washington in our primary ag-production areas,” Beers said. “Usually, the last frontier is to move out into agricultural areas.”

Small you-pick operations within the city limits of Vancouver, Wash., have been the only significant agricultural impacts seen to date, consistent with the pest’s preference for temperate, urban locations.

The pest typically overwinters in homes and avoids the climate extremes typical of the interiors of British Columbia and Washington.

While the number of bugs detected in Eastern Washington surged into the hundreds this year from just a few dozen in 2015, the largest numbers were found in the residential areas of Yakima and Walla Walla.

Walla Walla grapegrowers aren’t expressing alarm, however. Jason Magnaghi, viticulturist with Figgins Family Wine Estates in Walla Walla, said the pest isn’t present at levels that would damage wine quality.

While a crushed stink bug produces an unpleasant odor and could potentially taint wines in a manner similar to Asian lady beetles, Magnaghi said the insects have been drawn more to orchards than vineyards.

“Grapegrowers right now seem to be not so much threatened by this pest as a number of other crops—especially if they’re making their grapes into wine, which the vast majority of grapegrowers are,” Beers said. “The threshold tolerance seems to be really high. I believe what I’ve heard mentioned is four bugs per cluster of grapes, as you harvest them.”

According to rules of thumb from the Washington Association of Wine Grape Growers, each vine has about 40 clusters, and there are approximately 400 vines per acre. At this rate, a grower would need approximately 64,000 bugs per acre to detect a problem in finished wine, and detections in Washington this past summer maxed out at two bugs for an entire vineyard.

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