Grapevine virus diseases are of serious concern for vineyard managers and winemakers in all Western production regions. Grapevine red blotch-associated virus (GRBaV) impacts grape berry quality. Growers and scientists alike have noticed a consistently lower °Brix at harvest of infected vines, resulting in removal of symptomatic vines from vineyards. What’s more concerning is that GRBaV is spreading. Ecological mapping of GRBaV-positive vines, as verified by qPCR during 2013-2016, showed a significant trend of virus increase in two of three areas studied in Oregon.

During 2016, Dr. Vaughn Walton along with Dr. Kent Daane (University of California), Daniel Todd Dalton (Oregon State University), Rick Hilton (Oregon State University/Southern Oregon Research and Extension Center), Dr. Clive Kaiser (Oregon State University/Umatilla County Extension Service), Dr. Sudarshana Mysore (USDA-ARS, Department of Plant Pathology, University of California Davis) and Dr. Frank Zalom (Professor, Department of Entomology and Nematology, University of California Davis) began investigating vector-related field epidemiology for grapevine red blotch-associated virus.

Three potential virus vector insects were found in Oregon vineyards. Spissistilusfestinus was found in Southern Oregon and was recorded in all production regions throughout Oregon during the last 100 years (data from OSU insect collection). The treehopper species (Membracidae) Tortistiluswickhami and T. albidosparsus were found in Oregon vineyards. Tortistiluswickhami was predominantly found in Southern Oregon, with lower numbers of S. festinus and T. albidosparsus. Tortistilusalbidosparsus was predominantly found in the Willamette Valley. The seasonal population levels of T. albidosparsus, feeding and egg-laying levels in relation to temperature were described for the Willamette Valley. All suspected vector insect species were consistently found in vineyards where GRBaV spread year over year. The spread of GRBaV is alarming, with observed doubling and a 10-times increase in study sites from 2014-2016.

These treehoppers are the most likely species vectoring red blotch between vines. The patterns of virus spread within vineyards closely link feeding symptoms of treehoppers. The research team’s data indicate that GRBaV-infected plants are concentrated and spread from the edge of the sampled vineyard blocks. Virus transmission biology work is currently ongoing (three months post-inoculation) with more than 600 plants in greenhouse trials. During 2016, the research team reached approximately 800 growers though the different channels as part of the extension objective.