First identified in 2011, grapevine red blotch associated virus continues to be the focus of several research projects as little is known about how the disease is spread in vineyards. Infected vines often display symptoms that mimic those of grapevine leafroll disease, causing confusion when conducting a visual inspection.
“We believe that a lot of the 
previous vines that were tested for leafroll that were negative but showing symptoms, probably had this other pathogen, this other virus called red blotch,” said Biological Control Specialist for UC Berkeley Kent Daane. “We’re still trying to positively determine what is moving this pathogen around and one of the issues with this is that this particular pathogen doesn’t show up immediately in terms of expressing symptoms.”
Evaluating vineyards in Napa and Sonoma, Daane and his team hope to narrow down the possible vectors for the virus in order to develop effective control measures. Several different leafhopper species have tested positive for the virus, but that does not necessarily mean that it is a vector. There is still investigating required to accurately identify how the virus is transmitted through vineyards.
“We’ve found two common leafhoppers and one common Membracidae which is a treehopper that are both in the vineyard and tested positive for the pathogen,” said Danne. “In our tests with them we still haven’t found any of them to move the pathogen into a vine and that’s going to be the hard part.”
Not only is red blotch difficult to identify due to similar symptoms of leafroll disease, but infected vines can grow for two to three years before showing any symptoms of the pathogen. “That just adds to the length of the study and adds to how long it’s taking us to come up with the answer to some of our trials,” Daane noted.
At the recent 2019 San Joaquin Valley Grape Symposium Daane highlighted some of the research he has been working on noting a significant gap in understanding between leafroll disease and grapevine red blotch. Grape leafroll viruses have been closely studied for about 40 years through research conducted in a variety of areas including Australia, New Zealand, Europe, South Africa, as well as the U.S. “We know so much about the leafroll vectors and that allows us to develop a control program. We know so little about the movement or the epidemiology of red blotch,” said Daane.
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