Wine Grape Growers Face Reality
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.
 Naidu Rayapati. |
“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 Leads Extension Team Focusing on Plant Diseases
Naidu Rayapati, Washington State University grape virologist, 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.
“Multidisciplinary research is often the most effective approach to develop solutions to complex problems in agricultural production systems,” Rayapati said. “The long term goal of the project is to promote healthy growth of the state’s wine grape and small fruit industries by being the primary resource for contemporary, science-based information on diseases of wine grapes and small fruits and their management.”
He said the main objective of the project is to provide growers with best management practices to deal with diseases.
“During the initial phase of this two-year project, our primary focus will be on grapevine leafroll disease in wine grapes and virus diseases of blueberries,” Rayapati said. “We will update growers and nurseries on what we are doing via the Web and other communications tools. We also will be promoting the planting of virus-tested materials as the best defense against virus diseases in grapes and small fruits.”
The team includes WSU scientists and extension faculty in Pullman, Prosser, Puyallup, and Mount Vernon, a representative of the Washington wine grape industry, plus collaborators at the University of Idaho and USDA-Agricultural Research Service in Corvallis, Ore.Podcasts
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Grapevine Leafroll Disease
Grapevine leafroll disease accounts for about 60 percent of the production losses of grapes world wide, according to Naidu Rayapati, Washington State University grape virologist. It is one of the most complex viral diseases known to infect plants. Nine viruses are so far been found associated with the disease. They are called grapevine leafroll-associated viruses (GLRaVs).
Three of these viruses associated with the disease were detected in a 2000 survey of Washington vineyards. A reconnaissance study for the past three years revealed the occurrence of another three viruses in wine grapes showing leafroll disease symptoms. Among them, GLRaV-3 was found to be the most predominant and widely distributed in different wine grape cultivars.
The disease can delay ripening, cut yields as much as 50 percent (or more depending on the severity of infection) and have a major impact on fruit quality. Once infected, vines cannot be treated. The disease can be eradicated only by pulling the vines.
Symptoms don’t materialize until late summer. The leaves of red grape varieties turn red with the principal veins in the leaves remaining green.
“At the end of the season, you will see classic symptoms of downward rolling of leaves in red grape varieties,” Rayapati said,
Symptoms are less pronounced in white grapes, evidenced by a slight yellowing and cupping of the leaves in some varieties. Concord grapes may show no symptoms.
“Lack of symptoms does not mean the virus is not present,” Rayapati said.
He added that presence of symptoms also does not necessarily mean the vines are infected. Nutrient deficiency and injury to plants presents similar symptoms.
In his laboratory at the WSU Prosser Irrigated Agriculture Research and Extension Center, Rayapati and his staff tests plant samples as part of research to document viruses in the state’s vineyards. Results are confidential and shared only with the respective grower. The ELISA lab conducts testing for different viruses on a cost basis.
Rayapati also visits vineyards at the invitation of growers to examine suspicious vines.
Humans, are regarded as the primary ‘agents’ of disease spread through the distribution of infected cuttings or grafting of infected material. The disease can also be spread by grape mealybugs, which are found in the state.
“Utmost vigilance is required while bringing cuttings from places like California where vine mealybugs are found,” Rayapati said. “The vine mealybug is a more efficient in spreading the virus than grape mealybug.”
It is thought that the disease possibly may be spread from plant-to-plant during pruning or root-grafting. However, no definitive evidence is available to confirm this possibility. Rayapati is working with growers to understand the field spread of the disease.
Contact Naidu Rayapati for advice.
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