Vineyard & Winery Management

January - February 2012

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VINEYARD Grapevine Leafroll Disease rapevine leafroll disease is a problem in vineyards world- wide that reduces grape yields, causes premature decline in individual vines and vineyards, and reduces fruit quality for wine production. The Grapevine Leafroll and Vitivirus Dis- eases Seminar, presented at the 2011 American Society for Enol- ogy and Viticulture (ASEV) National Conference in Monterey, Calif., explored issues and presented research updates regarding this increasing problem for vineyards. GLOBAL AND U.S. OVERVIEW Grapevine leafroll associated viruses (GLRaVs) affect vineyards in Europe, South Africa, New Zea- land, Australia and North America. An estimated 60% of virus-related vine losses are caused by lea- froll. In the U.S., leafroll is found in vineyards in California, Oregon, Washington, Idaho, Michigan, Mis- souri, New York and Virginia. Lea- froll affects Vitis vinifera, hybrids, rootstocks and native cultivars, although symptoms can be vari- 68 VINEYARD & WINERY MANAGEMENT JAN - FEB 2012 Symptoms of leafroll disease include red leaves with green veins and downward curling, as shown here. a Continuing Problem Clean vines, mealybug control needed to prevent spread By Ted Rieger, senior feature editor able. Concords in New York often test positive for GLRaVs even while showing no symptoms. Visible leafroll symptoms, most common in late summer and fall, include: red leaves (often with green veins) and downward curling in red varieties; leaf discoloration, yellowing, chlorosis and curling in white varieties. Symptoms can be similar to other diseases and nutritional problems, so lab test- ing to confirm the virus is sug- gested. Problems caused by leafroll include: delayed or incomplete fruit ripening/maturity, lower sugar, increased acidity, reduced antho- cyanins, poor wine quality/color, reduced yields, reduced economic returns, and premature loss of vine productivity requiring replanting of individual vines or vineyards. The recent surge in research about leafroll in the U.S. was prompted by documentation of its rapid spread across two Napa Valley vineyard blocks from 2002- 2008 in which leafroll incidence increased from 23% to 66%. The presence of grape mealybugs vec- toring leafroll was a possible factor in its spread here. In addition, the prevalence of AxR-1 rootstock in Napa Valley, prior to major replants due to phylloxera, may have sup- pressed expression of leafroll symptoms. More recently planted, phylloxera-resistant rootstocks may be more susceptible to leafroll effects than AxR-1. Leafroll symptom expression AT A GLANCE Leafroll disease affects vineyards worldwide, resulting in reduced yields, vine decline, delayed rip- ening and reduced fruit and wine quality. Using clean and certifed plant material is the best strategy to prevent occurrence and spread of leafroll. All leafroll viruses are graft trans- missible, and several are vectored by mealybugs. Virtually all cultivars can be affected by leafroll, but rootstocks may vary in susceptibility. WWW.VWM-ONLINE.COM

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