Issue link: http://winesandvines.uberflip.com/i/116287
APRIL NEWS Pinot leaf curl has been striking with greater severity in recent years. Location Is Key Factor For Pinot Leaf Curl S anta Rosa, Calif.—Pinot leaf curl, the vine disorder that struck Sonoma County's Pinot Noir vineyards with increasing severity during the cooler vintages of 2010 and 2011, appears to be a nitrogen disorder mainly triggered by the site conditions of a vineyard. winesandvines.com Rhonda Smith, University of California Learn more: Search keywords extension advisor for Sonoma County, "Pinot leaf curl." discussed the condition Feb. 20 during the Sonoma County Grape Day event, which included researchers discussing other issues of interest for growers. During the same event last year, Smith and University of California, Davis, professor Doug Adams described the leaf-curl disorder and theorized about possible causes. Based on the symptoms, they suspected a nitrogen disorder that led to the plants producing the toxic compound putrescine. The disease can cause vine leaves to curl downward above necrotic sections of vine shoots. Severe cases of the sickness can lead to thick bands of necrotic tissue that stunt shoots and reduce yields. Smith sampled 14 vineyard blocks by pulling symptomatic and normal-looking vine leaves. Those leaves were analyzed for the presence of putrescine, and 12 of the 14 samples showed higher levels of the compound in leaves exhibiting symptoms. She stressed there is no "normal" level of putrescine in blade tissue. Because of the nitrogen connection, Smith said growers that have had to deal with the disorder are advised not to make any nitrogen applications to their vines in early spring. Smith said it ultimately appears that the largest contributing factor to the severity of the disorder is the vineyard location and especially minimum daily spring temperatures. Dr. Rodrigo Almeida, an entomologist with UC Davis, offered an update about current leafroll virus research. He said researchers found mealybugs with the virus only needed one hour to infect more than 25% of the plants in the study. "This process of transmission happens very quickly," he said. Another study found that vines could show symptoms of leafroll as well as reduced Brix levels in just one year. Researchers in Napa also found variants of the virus in a vineyard block that did not appear to come from adjacent vineyards. Almeida said those findings indicate the disease and its vector can be brought in on the wind. "Even if your adjacent neighbors are doing a good job, these infections can come from far away," he said. —Andrew Adams 18 W in e s & V i ne s AP R I L 2 013