PROSSER, Wash. – In order to grapple with one of the wine grape industry’s rising concerns–how to deal with grapevine leafroll virus disease–a small group of wine grape growers, certified nurserymen, representatives from the Washington, Oregon and Idaho state departments of agriculture and Washington State University faculty recently gathered at WSU’s Irrigated Agriculture Research and Extension Center in Prosser.
“Virus diseases like grapevine leafroll are firmly rooted here,” said Naidu Rayapati, WSU grape virologist. “It’s time to face reality and develop strategies to mitigate the problems caused by viruses.”
Grapevine leafroll disease, which is found world-wide, 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.
The meeting was one of a series organized to take stock of the current situation with regard to virus disease problems in wine grapes, develop a coordinated approach at the regional level to confront the challenges ahead and translate ideas and opinions in to action.
A few years ago, it was estimated that nearly 10 percent of Washington’s vineyards have grapevine leafroll disease. Anecdotal evidence suggests that the disease is more wide spread 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 said.
As part of an industry-led initiative, Rayapati was hired by WSU 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,” said Rayapati. “This information is critical for designing appropriate strategies to tackle virus diseases in our vineyards.”
Leafroll-virus nfected 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,” said Gwen Hoheisel, WSU Benton and Franklin County Extension educator. “Your first line of defense is to remove the infected vine and re-plant 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 said. 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 explained.
“Certification has no real value if the cuttings are not tested for all currently known viruses using state-of-the-art technologies,” Rayapati said. “That is where partnerships between regulatory agencies, certified nurseries, growers and scientists play a critical role to ensure planting virus-tested cuttings.”
“No doubt that grapevine leaf roll disease is a serious threat, if not contained,” said Hoheisel. “The problem has been with us even before we realized, but it is something we need to learn to manage for the prosperity of the wine-grape industry. And the sooner the better.”
Rayapati is leading a WSU Extension issue-focused, team-based project on raising awareness and finding solutions for key viral and fungal diseases affecting grapes and other small fruits in Washington state.
For more information on WSU’s efforts to provide growers with certified virus-free planting stock, please visit the Northwest Grape Foundation Service Web site at http://nwgfs.wsu.edu/.
WSU Grape Virology – resource and information Web site for grape growers
Leafroll Virus – information for reporters
Northwest Grape Foundation Service – resource and information about obtaining certified virus-free plant material