"Red Blotch Disease" appears to be a "new" virus in California vineyards.
The UCD Extension put out the following information regarding "Red Blotch" today:
If you weren’t able to attend the UCD Extension seminar yesterday entitled “Current Issues in Vineyard Health”, you missed a very important discussion of the newly-discovered viral disease hitting California’s vineyards: for lack of a better name, Red Blotch disease.
Its symptoms distinguish it from Leafroll Virus, as does its PCR fingerprint. For the most complete information available on the disease, please see the attached brochure, developed by Dr Jim Wolpert, our Viticulture Extension Specialist, and Dr Mysore Sudarshana, a researcher in Plant Pathology at UC Davis.
If you just weren’t able to get your grapes up to target Brix this year, or if your field samples fell well short of your expectations, you might consider Red Blotch as the reason. It always helps to understand your roadblocks, and maybe pick, or thin, accordingly.
I'm no viticulturist, without this genetic study, I very much doubt that I would have been able to tell the difference between "Red Blotch" and Leafroll virus.
Napa Valley Grapegrowers is encouraging their members to:
Please consider these questions on a block-by-block basis, choosing the block of greatest interest, or more than one if you have time:
1. Did you see Red Leaf (RL) symptoms in 2012?
2. Did you see RL symptoms in previous years?
3. Is the incidence (% RL symptom vines) increasing?
4. Do you have a count of the number of vines with RL symptom?
5. Do you have a map of the vine showing RL symptoms?
6. Have you taken any photos of the symptoms?
7. Have you done any virus testing of RL symptoms?
8. Did you compare the sugar accumulation between RL and non-RL vines?
9. Did you or your winemaker/buyer decide not to pick RL symptom vines in 2012?
NVGG also posted a PDF of Dr. Sudarshana's brochure.