St. Paul, Minn. (January 12, 1999)—The best-tasting wines are produced from healthy, robust grapes. Yet, keeping grapes healthy is a formidable task for growers, especially with a persistent fungal disease problem like powdery mildew. Powdery mildew has been a constant challenge in California vineyards for more than a century. Now, with the help of University of California plant pathologists, growers can effectively control the powdery mildew in their orchards through the increase of technology and decrease of chemicals. The powdery mildew pathogen belongs to a large group of fungi that attack many different types of plants worldwide. "As the fungus grows over grape surfaces, it sinks its ‘teeth’ into the succulent plant tissues providing itself with food to grow and reproduce," says Douglas Gubler, plant pathologist at the University of California and a member of the American Phytopathological Society (APS). "The result is reduced plant growth, and poor quality fruit." Finding alternative ways to control powdery mildew took close observation by plant pathologists. "We identified, through our research, the environmental parameters that result in severe disease," says Gubler. "By using the temperature, moisture and time parameters we developed the UC Davis Powdery Mildew Risk Index, a computer program forecasting model, which provides daily disease tracking information to growers." Growers are now able to predict how severe the disease will be in a week or two and can determine which fungicides will be most effective as well as the rates and intervals between application. "Compared with standard spray programs, this forecasting model lets growers apply two to three fewer fungicide applications during the growing season with equal or better disease control," says Gubler. "That means better grapes for wine production and potentially fewer fungicide applications which is easier on the environment." For more details on the forecasting model for powdery mildew, visit the APS feature story with photographs and links to additional sites at www.apsnet.org/publications/apsnetfeatures/Pages/UCDavisRisk.aspx. The American Phytopathological Society (APS) is a professional scientific organization dedicated to the study and control of plant disease with 5,000 members worldwide.