Courtesy University of California/Agricultural Research ServiceScientists at the University of California and the Agricultural Research Service continue research on a new malady of winegrapes that's been dubbed grapevine red blotch disease.
Although the symptoms resemble those of leafroll disease, genetic testing has differentiated it from the viral leafroll disease, according to an informational brochure.
Vines with red blotch produce fruit clusters with reduced sugar content, causing delayed harvest.
In addition, the disease occasionally causes poor color and higher acidity in the berries.
It was first found in 2008 in cabernet sauvignon vines on rootstock 101-14 in research plots at UC's Oakville Research Field Station near Oakville, Calif.
Laboratory testing by both public and private services failed to detect any leafroll virus in the vines.
So far, disease symptoms have been found in red varieties, including cabernet franc, cabernet sauvignon, merlot, petite sirah, petit verdot and zinfandel.
In addition to the Oakville site, it has been found in commercial plantings in Napa, Sonoma, San Louis Obispo and Fresno counties.
For more information, download an informational flier from the University of California.