Viticultural Information

Subject	Red Blotch Disease
Description	Red blotch and red veins on a leaf of Cabernet Franc grapevine A newly discovered grapevine virus has been discovered associated with a set of disease symptoms which is being called ‘Red Blotch Disease’. The symptoms generally start appearing in late August through September as irregular blotches on leaf blades on basal portions of shoots. The secondary and tertiary veins turn partly or fully red. Occasionally, the reddening of leaf blade in the interveinal zones between secondary veins resembles those of leafroll diseases, but the leaf margins are not seen rolling downward. The most important symptom of this disease appears to a reduction of the Brix levels of infected vines. It is not known if the disease has any effect on fruit yield or vine longevity. So far, the disease symptoms have been noticed in vineyards planted with red grape varieties such as Cabernet Franc, Cabernet Sauvignon, Merlot, Petite Sirah, Petit Verdot and Zinfandel. In addition to North Coast vineyards in Napa and Sonoma Counties, diseased vineyards have also been found in Central Coast (San Luis Obispo County) and San Joaquin Valley (Fresno County). Grapevine red blotch does not appear to be of recent origin. This disease escaped attention of vineyard owners and managers because of leafroll-like symptoms. This also means that diagnosis based on the leaf symptoms can be challenging. A molecular assay, DNA-based PCR, is currently available and the virus can be detected in the petioles of basal leaves, much before the onset of symptoms, and also in dormant canes.
People	Maher Al Rwahnih, Mysore R. Sudarshana, Jim Wolpert
Links	On March 27, a special webinar Grapevine Red Blotch Disease: An Emerging Issue was held, moderated by Tim Martinson, Senior Extension Associate at Cornell University. Cornell University virologist Marc Fuchs, University of California Cooperative Extension Viticulture Advisor Rhonda Smith, and University of California Davis Foundation Plant Services director Deborah Golino can be seen online with current updates on Grapevine Red Blotch associated Virus (GRBaV), it’s effects on vineyards, and its status in planting material. http://grapesandwine.cals.cornell.edu/cals/grapesandwine/outreach/viticulture/ncpn-red-blotch.cfm Held on February 21, 2013 at UC Davis, the Wine and Wine Grape Research 2013 event showcased current viticulture and wine-related research projects as 20-minute talks by researchers. Links to individual presentations are below. After clicking on a link, notice the 5 icons on the upper right of the screen. The first icon with inward arrows turns the screen into full screen; the second icon turns it into a picture in a picture; the third icon makes it into a side by side picture; the fourth icon makes a single picture of the slide or the presenter, the last icon swaps the slide and the presenter. Deborah Golino, Director, Foundation Plant Services Description: Red Blotch Status of the Classic Foundation Vineyard and the Russell Ranch Foundation. Mysore Susarshana, USDA ARS, UC Davis Description: A DNA virus associated with grapevine red blotch is widespread in California vineyards.
Publications	Al Rwahnih, M., Dave, A., Anderson, M., Uyemoto, J. K., and Sudarshana, M. R. 2012. Association of a Circular DNA Virus in Grapevines Affected by Red Blotch Disease in California. Proceedings of the 17th Congress of the International Council for the Study of Virus and Virus-like Diseases of the Grapevine (ICVG), Davis, California, USA, October 7-14, 2012, 104-105. View the Article Mysore Sudarshana, USDA-ARS, and James Wolpert, Viticulture Extenstion Specialist at UC Davis, put together a brochure on Grapevine Red Blotch. The brochure features sections on disease symptoms, etiology, and diagnosis. View the Brochure The National Clean Plant Network for Grapes put together a fact sheet discussing symptoms and treatments for Grapevine Red Blotch. The fact sheet includes a side-by-side comparison to Grapevine Leafroll. View the Fact Sheet Dr. Deborah Golino, Director of Foundation Plant Services, released a statement on the status of Grapevine Red Blotch Disease in the Foundation Plant Services Vineyards. View the Press Release Practical Winery and Vineyard featured an article in their April publication on Grapevine Red Blotch and the new technology used to identify it. View the Article Maher Al Rwahnih, Ashita Dave, Mike Anderson, Adib Rowhani, Jerry K. Uyemoto, and Mysore Sudarshanna. 2013. Association of a DNA virus with Grapevines affected by Red Blotch disease in California. Phytopathology. View the Article

This website is a work in progress of the University of California (UC) Division of Agricultural and Natural Resources (ANR) Integrated Grape Production Workgroup. It is designed to increase accessability to the work of UC researchers, including faculty, Cooperative Extension (CE) specialists, CE advisors, and staff. UC Researchers interested in contributing content are invited to contact Deborah Golino dagolino@ucdavis.edu to discuss possible contributions.