Industry meets to address grapevine leafroll virus

A small group of winegrape growers, nurserymen and experts from Pacific Northwest universities met recently to address one of the industry’s rising concerns—grapevine leafroll virus disease.

“Virus diseases like grapevine leafroll are firmly rooted here,” says Naidu Rayapati, a Washington State University grape virologist in Prosser. “It’s time to face reality and develop strategies to mitigate the problems caused by viruses.”

Grapevine leafroll disease, which is found worldwide, can cause a marked decline in grapevine vigor, grape quality, and productivity. The disease can reduce yields as much as 50 percent or even more, depending on the severity of infection.

A few years ago, it is estimated that nearly 10 percent of Washington’s vineyards will have grapevine leafroll disease. Anecdotal evidence suggests that the disease is more widespread than previously thought, raising alarm among industry stakeholders.

“If appropriate measures are not taken, the disease could have direct impact on

the sustainability of the wine-grape industry in the state,” Rayapati says.

As part of an industry-led initiative, Rayapati was hired by the university in 2004 to ramp up efforts to address virus diseases in wine grapes and set the direction of virus disease control programs

Rayapati’s research for the past three years has documented many grapevine viruses occurring as single or mixed infections.

“Knowing what is out there is part of dealing with the problem,” Rayapati says. “This information is critical for designing appropriate strategies to tackle virus diseases in our vineyards.”

Leafroll-virus infected vines must be replaced because there is no treatment for the disease. While some growers are aggressively pulling infected vines at the first sign of disease, others aren’t.

“It’s not everybody’s practice,” says Gwen Hoheisel, a WSU Extension educator in  Benton and Franklin counties. “Your first line of defense is to remove the infected vine and replant in that spot with a virus-free cutting. If your entire vineyard is infected, that is a different decision a grower has to make.”

While recent research in California has confirmed that the grape mealybug spreads the virus, humans are probably the primary means of spread—through the propagation of infected vegetative cuttings.

The best insurance against the disease is to plant material that is certified to be virus free, Rayapati says. An anticipated shortage of certified planting material may tempt growers to take shortcuts by bringing cuttings from outside the state or using cuttings from existing vineyards.

If growers buy certified material from other states, they should be aware of what viruses have been tested. Not all certified material is tested for the same viruses, Rayapati says.

“Certification has no real value if the cuttings are not tested for all currently known viruses using state-of-the-art technologies,” he says.

“That is where partnerships between regulatory agencies, certified nurseries, growers and scientists play a critical role to ensure planting virus-tested cuttings.”

For more information on grape leafroll virus, visit http://wine.wsu.edu/virus.

For more information on WSU’s efforts to provide growers with certified virus-free planting stock, visit the Northwest Grape Foundation Service Web site at http://nwgfs.wsu.edu/ or the University of California’s Foundation Plant Material Service at http://fpms.ucdavis.edu/index.html.

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