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July 2017 WINES&VINES 19 WINE INDUSTRY NEWS S an Luis Obispo, Calif.—The welcome end of a four-year drought brought one unexpected hardship to some California wine grape vineyards: downy mildew. Veteran extension viticulturists said the pathogen is a rarity in the Golden State and blamed its emer- gence on uncommon rates of humidity. This spring, University of California Coop- erative Extension advisor Mark Battany docu- mented downy mildew in vineyards in both San Luis Obispo and Santa Barbara counties. "We don't know much about how this downy mildew might play out here; it's not something we've ever experienced on a significant scale," Battany told Wines & Vines. "It's a learning process for all of us. There is a lot of informa- tion about it from elsewhere in the country, so the disease is well understood, just not how it might be a factor here in this region or else- where in the state." Despite its friendly sounding name evoca- tive of baby ducklings, downy mildew is not a pretty disease. It can infect all green tissues of the vine. The pathogen manifests through leaves with yellowish spots on the top and a char- acteristic white, fluffy growth on the under- sides. Infections of the flower grape clusters can lead to complete necrosis; infected shoots can have partial infections or become fully infected and collapse. This year's warm, wet spring after drench- ing winter rains created "perfect conditions" to incubate downy mildew, according to Bat- tany. He called downy mildew a very aggressive disease with the potential to cause major dam- age if left uncontrolled. Battany cautioned growers in coastal areas to scout vigilantly for the disease and treat it accordingly. He said infections were observed in areas including the Paso Robles AVA. Precipitation, he added, could create condi- tions conducive to rapid spread of infections. The Integrated Pest Management program at the University of California advised: "Preven- tive fungicides must be applied before an infec- tion period begins. New growth following application will not be protected. Include a spreader/sticker agent to prevent the material from washing off with rain." Larry Bettiga, viticulture advisor for neigh- boring Monterey County, told Wines & Vines he'd had no reports of the disease in his area and said that while technically it is not an in- vasive pest, he hasn't seen it in California for at least 10 years. Rhonda Smith, the UC viticulture advisor for Sonoma County, said she has never seen downy mildew in that North Coast region. "It's never been an issue here, but no cultivars are immune to it." This spring has brought warm, damp nights, and Smith said that these conditions can make vineyards more vulnerable to the disease. —Jane Firstenfeld MARK BATTANY / UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION White, fluffy growth on the underside of leaves is the hallmark trait of downy mildew. Downy Mildew Identified in California's Central Coast Vineyards For more information contact your sales representative or email us at info@seguinmoreau.com ICONE RANGE F inesse