Vine Mealybug in Oregon?

Single insect found in vineyard may be notorious grape pest

by Peter Mitham
Vine Mealybugs spotted in Oregon
Adult female vine mealybugs and crawlers
PHOTOS: Jack Kelly Clark, University of California
Hillsboro, Ore. -- One of the most invasive vineyard pests on the West Coast may have been found in Oregon, prompting a statewide alert. An unidentified species of mealybug was found on the roots of vines in an abandoned vineyard near Hillsboro in northwestern Oregon on Sept. 15. An initial examination indicated the insect may have been a vine mealybug.

Vine mealybug has been hitherto unknown in the Pacific Northwest but it spreads quickly and is a vector of grapevine leafroll virus, which reduces the photosynthetic capabilities of infected vines. Dr. Vaughn Walton of Oregon State University told Wines & Vines that accurate identification of the Hillsboro mealybug is not expected for several weeks, pending lab studies.

The Hillsboro discovery, which Walton said was the first recorded instance of mealybugs in a northwestern Oregon vineyard, consisted of a single mealybug and a few young crawlers. Subsequent examinations found no additional bugs on the property, but that's not to say they're not there. Pheromone traps are in place on adjacent properties for monitoring purposes.

How to spot mealybugs

A factsheet distributed by OSU Viticulture Extension recommends that growers inspect all grapes on the crushpad for signs of a mealybug infestation, including:
  • Honeydew and sooty mold growing on honeydew, which is mealybug excrement;
  • A significant presence of ants;
  • The presence of mealybugs or young crawlers.
A mealybug that's part of an infestation is often coated with large quantities of white wax on its body.
Source: Oregon State University Viticulture Extension.
"Mealybugs are extremely inconspicuous. They hide under the bark, in the soil, and you never really see it until it's a big issue. And you don't want to get into that type of situation," Walton said. "Once they've got a foothold, it's virtually impossible to get them out."

That fact spurred the Oregon Wine Board to alert growers to the discovery within days of the report, with a view to preventing the spread of the unknown bug. "We're just helping raise awareness of what people should do. It's not a time to panic," said Ted Farthing, the board's executive director. "This is a known problem in other places. But we want people to help us--if they find any, to know what they're looking for."

Farthing noted that mealybugs have been a manageable issue in other states where they're known to exist (including California), but it is key to keep one step ahead by limiting the spread.

"That's why we believe it's very important to be vigilant," Walton said.

He urged growers to take precautions to prevent mealybug populations from spreading as crush season begins. Keeping pomace out of the vineyard is a key means of preventing the bugs from becoming established. The females' egg sacs can survive crush, and if these find their way into pomace and in turn into compost that's spread on vineyards as a soil amendment, an infestation typically follows.

Vine Mealybugs spotted in Oregon
Vine mealybugs infest a grapevine trunk.
"You always run the risk of infesting a vineyard, especially if you're getting fruit from an area where you know you've got mealybugs," he said. Walton also advised taking steps to kill the bugs, such as hot water treatments or by covering compost with plastic tarps that effectively bake the pomace and reduce the insect population. Composted pomace should not be used in vineyards, however.

Washington growers will be watching the outcome of the Oregon discovery closely, said Dr. Doug Walsh, an entomologist at Washington State University in Prosser, Wash. The bug is a difficult pest because it can overwinter in the roots of vines, Walsh said, which insulates it from both the effects of severe cold and most available pesticides.
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