Oregon’s wine industry, worried about the threat of vine mealybug and potential for rapid spread of grapevine leafroll virus, is taking proactive steps to try to keep the pest out of the state. The wine industry is particularly worried about finding vine mealybug because plant material and harvested grapes routinely come from areas where there are known infestations, such as California, where vine mealybugs and the disease are widely present.
The impact from leafroll disease on fruit quality can be pretty severe, said Dr. Vaughn Walton, Oregon State University Extension horticultural entomologist. Growers in Oregon’s Willamette Valley—a cool climate region with few heat units—are especially concerned about the disease potential, he said. "If they get the virus there, they know they will have difficulty ripening their grapes."
OSU researchers have recently begun trapping with pheromone lures and sticky traps and using D-vacs, sweeping nets, and peeling trunk bark to look for mealybug species in Oregon’s grape-producing areas. Scientists are using synthesized pheromone for grape, obscure, and vine mealybug, developed by the University of California, Riverside, to help map mealybug populations. Though the grape mealybug pheromone is not yet readily available, pheromone for the vine mealybug is commercially available, according to Walton.
The pheromone lures and traps helped the researchers detect grape mealybug in southern Oregon vineyards. "We did find that more areas in southern Oregon were infested with grape mealybug than we originally thought, but fortunately, there was no vine mealybug infestation," Walton said.
Washington State University entomologists are also working with lures and pheromone traps to monitor for vine mealybug. Thus far, Washington remains free of vine mealybug, however, grape mealybug is established. Some growers, concerned about the spread of leafroll virus, have adopted a zero tolerance for grape mealybug in their vineyards.
Northwest scientists are using developmental thresholds to model how quickly vine mealybug could reproduce in the Pacific Northwest under the cooler climates of Oregon, Washington, and Idaho. Based on the model, Walton predicts that southern and eastern Oregon, eastern Washington, and Idaho could potentially have three to four generations of vine mealybug per season; western Oregon and western Washington could have two to three.
"Three to four generations could mean pretty rapid spread of vine mealybug and the potential spread of leafroll virus," he said. In Idaho, there are now also confirmed findings of grape mealybug, he added.
In outlining strategies adopted in Oregon to help keep leafroll disease from getting a stronghold in the state, Walton said that OSU plans to continue to trap extensively for mealybugs.
Grower education is also part of industry’s prevention tactics. "Making sure you have virus-free planting material is the best way to control the virus," he said.
Oregon grape growers and wineries are discussing the need for a protocol that would better regulate plant material and movement of fruit coming from potentially infested nursery plant material. "Many would like to develop a system that would limit the movement of plant nursery material as well as harvested crops," he said, noting that many growers worry about the movement of grapes from areas with known vine mealybug infestation to Oregon wineries. In California, much effort is made to mitigate the spread of the vectors and virus to surrounding areas through research work of the University of California.
Walton advises growers to always start their management practices, such as pruning, suckering, tying canes, leaf removal or harvest, in blocks that have no known virus or mealybug infestation and then move workers to older vineyards, which are more likely to have leafroll virus. In this way, there is less likelihood of cross contaminating the virus- or vector-free blocks if they are managed first.