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Grounded Grapegrowing GLENN MCGOURT Y Answers About Leafroll Virus virus-free nursery stock began to show lea- froll symptoms a few years after planting. In most cases, these vineyards are planted adjacent to older vineyards that are show- ing leafroll symptoms. Previously, it was believed by many people that the main method of virus transmission was by prop- agating vines from infected wood and that, L eafroll virus has been an ongo- ing problem in the vineyard industry for many years. Re- cently, there has been height- ened awareness as some new vineyards planted to certified at least in California, insect transmission was not that significant. But closer studies are changing what was once seen as com- mon knowledge. We have many knowledge gaps, but as researchers begin to study this problem, we are starting to get some answers about how this disease is moved around and what are the likely sources of inoculum. As a University of California farm advi- sor, I consult very often with growers in my region on this topic. I will share with you 10 of the most commonly asked ques- tions as well as my best answers: Why has leafroll virus started to move suddenly into new vineyards planted with certified virus-free material? UC researchers working in Napa Val- ley have clearly demonstrated that young vineyards planted with virus-free nursery stock have been infected with leafroll vi- rus from adjacent older vineyards with the disease. Symptoms begin at the margins of the clean block and continue to spread over time through the newer vineyard. Since the advent of vine mealybug, ev- eryone has been concerned about its poten- tial as a vector to spread leafroll disease. It Register to Exhibit for Free FREE Early Exhibitor Registration ($500 value) open until December 31, 2011. Contact Jessica Braum Corbett at jbraum@VariantEvents.com to register. NationalWineExperience.com THE VOICE OF THE WINE INDUSTRY 60 Wines & Vines OCTOBeR 2011