University of California Cooperative Extension in Sonoma County has launched a new Web page on grapevine red blotch disease.
There's also a link to similar information in Spanish, Enfermedad de la Mancha Roja de la Vid.
The Sonoma County website contains color photos of leaf symptoms as well as links to additional information on the viral disease.
Although some North Coast grape growers have complained about the problem for several years, it wasn't until 2011 that a new grapevine virus was identified in diseased vines, according to the website.
Virologists from the UC Davis Foundation Plant Services and the U.S. Department of Agriculture Agricultural Research Service at Davis found the virus in diseased vines of cabernet sauvignon, cabernet franc and zinfandel.
The virus was identical to one isolated by Cornell University virologists from a cabernet franc vine.
Cornell virologists also identified the pathogen as a member of the geminivirus family. Some geminiviruses can be spread by leafhoppers and whiteflies, but it's not known whether leafhoppers or other insects can spread this new grapevine virus in the field.
A trial by Washington State University researchers found insects could move the virus to potted vines.
Now Cornell University virologists have to prove that the newly discovered virus is responsible for grapevine red blotch disease.