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Classic symptoms of fan leaf virus on Pinot Noir include yellowing leaf discoloration.

Classic symptoms of fan leaf virus on Pinot Noir include yellowing leaf discoloration.

Washington State grape growers should be on the look out for grape fan leaf virus, a troublesome virus that can affect berry size. Until recently, the disease had not been found in the state.

"We were under the impression that we didn’t have the virus here," said Dr. Naidu Rayapati, Washington State University virologist. But in 2007, scientists detected the disease in four wine grape cultivars in Washington—Pinot Noir, Chardonnay, Cabernet Franc, and Merlot. The disease was identified in different grower vineyards in geographically separated areas in Benton County, he reported.

"Anecdotal evidence indicates introduction of the virus through cuttings," he said, adding that his research team is working to better understand various aspects of fan leaf disease and prevent its spread through the distribution of infected cuttings.

Fan leaf is a serious virus because it affects the size of grape berries. "With fan leaf, we see tremendous reduction in the size of the berries," Rayapati said, noting that berry reduction occurs in both white and red cultivars.

Classic symptoms include yellowing of the veins of the leaves, but leaf discoloration is only seen in the spring and not in summer or fall.

Rayapati urged growers who see suspicious symptoms to contact him at: naidu@wsu.edu or call 509-786-9215.