Issue link: http://winesandvines.uberflip.com/i/591609
20 WINES&VINES November 2015 WINE INDUSTRY NEWS L odi, Calif.—Identifying grapevine viruses based on visual symptoms is the objec- tive of a new project by the Lodi Wine- grape Commission (LWC), which is working to develop an inspection protocol for grapevine red blotch-associated virus (GRBaV) and grapevine leafroll viruses. To initiate the proj- ect, the LWC held an experimental field work- shop, which was attended by several local pest control advisors and viticulturists. Plant pathology researchers Dr. Neil McRob- erts, Kari Arnold and their team of graduate student researchers at the University of Cali- fornia, Davis, have been working with LWC creating guidelines for growers collecting test samples based on different factors, including how much money the grower wants to spend on testing. Arnold discussed challenges in the sampling process. Viruses are not evenly distributed in a vineyard, or within a single vine. The samples tested in a commercial lab are sections scraped from part of a basal cane. Arnold pointed out, "Lab testing is more definitive, but it can still miss a virus—even in a virus-infected vine—if you don't get the right samples tested." LWC grower and program coordinator Dr. Matthew Hoffman pointed out that a UC Davis researcher was able to achieve 93% accuracy in positively identifying virus-infected vines based on visual symptoms. In comparison, laboratory testing of vine tissues is considered to be 98% accurate. Several challenges to visual identification exist, such as symptom variability by variety and season. Red grape varieties such as Cab- ernet Sauvignon, Cabernet Franc, Merlot, Petite Sirah, Petit Verdot and Zinfandel have been observed to have more obvious symp- toms of red blotch. White varieties may have yellowing and variable leaf color, but red blotch can be more difficult to identify visually in white varieties. Some mineral and nutrient deficiencies and fungal infections can also cause leaf discoloration similar in appearance to virus symptoms. A visual virus ID protocol would likely be best suited for red grape varieties. Based on observations during the field day, Hoffman listed several other points to include or address in formulating a protocol: Inspec- tion should involve looking at both sides of a vine in a vine row; inspectors should be famil- iar with symptoms based on variety; protocol(s) should consider the method of travel through the vineyard (walking, driving, ATV) and how much time to spend inspecting a vine, and groups of inspectors working together should have comparable ID skills to provide uniform assessments. "This is a big experiment, but we think it can be a cost-effective tool to help manage viruses," Hoffman concluded. —Ted Rieger Grapegrowers Explore Visual ID for Red Blotch Pest control advisor Charlie Starr and Matthew Hoffman of the Lodi Winegrape Commission inspect a vine for red blotch and leafroll virus.