Grapevine leafroll disease is easy to diagnose in red varieties, like this Cabernet Sauvignon vine, but more difficult in white varieties where the only symptom might be downward curling of leaves.

Grapevine leafroll disease is easy to diagnose in red varieties, like this Cabernet Sauvignon vine, but more difficult in white varieties where the only symptom might be downward curling of leaves.

The Washington grape industry has put a bull’s-eye on grape viruses and diseases and is going after its target in a big way. The Washington Wine Industry Foundation recently received a grant for nearly $250,000 to fund a clean-plant project designed to thwart what’s been identified as the principal threat to the state’s economic sustainability of the grape and wine industry.

Grape viruses, such as grapevine leafroll disease, have been a problem worldwide. The leafroll virus reduces overall vine performance, decreases the lifespan of vineyards, reduces yields and quality, and delays ripening, which, in a cool year like 2011, can be most challenging for Washington growers. Most viruses are spread by propagation of infected cuttings and vectors. There is no cure once infected vines take hold in a vineyard, so prevention—planting certified, virus-free plant material—is key.

Washington State University’s virology department has surveyed Washington vineyards for viruses since 2005. By 2009, it had tested some 2,000 samples from 35 vineyards. The most prevalent virus found was grapevine leafroll-associated virus-3, but other rugose wood complex viruses were detected, and vines often had more than one virus, according to WSU’s Dr. Naidu Rayapati. In addition, a limited number of samples were found to be infected with viroids like Australian grapevine viroid, hop stunt viroid, and grapevine yellow speckle viroid.

Enormous impact

“The potential economic impact is enormous,” said Vicky Scharlau, executive director of the Wine Foundation and project leader for the clean-plant grant. She cited a November 2010 study by Cornell University that estimated the cost of grapevine leafroll virus ranges from $547 to $16,014 per acre, depending on level of infection, method of remediation, and resulting reduction in yield and quality. In vineyards with an infection level greater than 27 percent, vine replacement was found to be the most viable option.

Based on Washington’s 61,000 acres of juice and wine grapes, Scharlau said that means potential losses for the state’s grape industry could be as high as $976 million a year for a single virus.

Scharlau also stated that grapevine leafroll virus has the potential to spread rapidly. A model for predicting viral spread, developed by New Zealand researchers, suggested an infection level of 50 percent in years 6, 8, and 11 in three vineyard plots observed in a 2004 study. The level was predicted to rise to 90 percent by years 11, 12, and 15.

Clean plants needed

WSU, in partnership with industry, replanted the university’s foundation block in 2004 and established the Northwest Grape Foundation Service to provide nurseries and growers with plant material that has been certified free of crown gall and viruses. But more is needed to ensure that the certified nurseries are propagating virus-free plant material, and that’s where the clean-plant grant steps in.

In the last few years, several Washington grape growers have planted “certified” material, only to find out that the plant material contained one or more viruses. Although the state agriculture department visually inspects mother blocks at certified nurseries, such efforts are inadequate to assure elimination of infected vines from mother blocks, said Mike Means, chair of the Foundation Block Advisory group. “The result has been the distribution of infected material to growers,” he stated in a letter ­supporting the grant proposal.

The grant will fund a survey of all mother blocks in Washington’s certified grape nurseries, testing plants by laboratory analysis to determine the level of viruses. Infected plants will be eliminated from the blocks. The survey will help ensure that the mother blocks—the source of current and future vineyards—will truly be free of leafroll and other viruses. The mother-block survey will take place in 2012 and 2013.

Survey results will be used to conduct a statewide clean-plant campaign in which information will be shared with industry and regulatory agencies on control, prevention, and management of viral diseases.

The grant will also fund the development of a pocket field guide of color photos of grape virus symptoms by grape variety to help growers and vineyard workers identify potential infections.

The project is funded through the U.S. Department of Agriculture’s Specialty Crop Block Grant program and administered by the Washington State Department of Agriculture. The clean-plant grant is in partnership with the Washington Association of Wine Grape Growers, the Plant Protection Division of the state agriculture ­department, and WSU.