March 6, 2013 By Diane Brown Michigan State University Extension
Mar. 6, 2013 – Grapevine red blotch is a newly recognized disease of certain red wine grape varieties and has so far been identified in California, New York, Virginia, Maryland, Pennsylvania, Texas, Washington and Canada.
It has not been reported in Michigan. A graft-transmissible DNA virus was consistently associated with the symptoms and has been identified by virologists in New York and California.
The virus was given a proposed name of grapevine red blotch-associated virus (GRBaV). A similar virus originally named grapevine cabernet franc-associated virus has been found in vineyards in New York and Pennsylvania, and an identical virus has been discovered in Canada. A molecular assay is used to detect the virus.
The virus was first identified in Cabernet Sauvignon grapevines grafted on rootstock 101-14 in research plots at UC Davis’ Oakville Station. Symptomatic vines have been found in commercial vineyards planted to varieties such as Cabernet Franc, Cabernet Sauvignon, Merlot and several others.
The canopy symptoms on the infected vines are somewhat similar to those seen with leafroll virus. More importantly, fruit clusters have reduced sugar content, which is also characteristic of leafroll, but no leafroll viruses could be detected in samples sent for laboratory tests. Other symptoms included increased acidity and poor colour development of clusters.
A new grapevine red blotch disease brochure with photographs and additional information about symptoms and diagnosis of grapevine red blotch disease has been developed by USDA Agricultural Research Service and is available for download.
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