Update on Red Blotch Disease in Grapevines

(Wines&Vines) - There was standing room only as growers and winemakers skipped the wine reception at the Nov. 13 Napa Wine + Grape Expo to hear the latest intelligence on red blotch virus from Dr. Marc Fuchs of the Department of Plant Pathology at Cornell University in Geneva, New York.

Fuchs preceded his talk by acknowledging that viticulturists don’t have all the answers yet; many questions remain about the newly identified virus, its transmission methods and ways to overcome it. Fuchs presented a similar presentation during an event hosted by the University of California, Davis' Foundation Plant Services. A video and slide show of his presentation can be found here.

Majority of growers have seen it

A show of hands of growers and vintners who see signs of red blotch in their vineyards was asked for. Most in the room raised their hands, a sign of the malady’s spread in Napa Valley and elsewhere. Fuchs said he’d get the same response among New York grapegrowers.

The symptoms of red blotch disease – more formally, grapevine red blotch associated virus (GRBaV) – were first described in 2008, and transmission by grafts was confirmed in 2012. The virus was also recognized that year, and an assay was developed to detect and confirm it. The first potential vector was identified this year. That short time line contrasts with 80 years to take those steps with leafroll virus and 120 years with fanleaf virus.

 The symptoms of the virus are red blotches and spots on leaves, though a small percent (2.5%) of infected vines don’t show any symptoms likely because of the latency of disease onset. The red ranges from pink to crimson. (Editor’s note: further description of GRBaV, numerous photos by Dr. Fuchs and others, and a short list of labs that can test for the virus can be viewed here.) Other viruses like leafroll also color leaves, but GRBaV displays a different pattern of red than leafroll