Issue link: http://winesandvines.uberflip.com/i/498427
26 WINES&VINES May 2015 WINE INDUSTRY NEWS N apa, Calif.—A researcher in New Zealand seems to have developed a regime to keep leafroll virus under control—but it's not clear whether the same approach will be equally successful in California due to differences in conditions, notably a different insect vector. Dr. Vaughn Bell spoke to the Napa Valley Vineyard Technical Group recently during a talk arranged by University of California Cooperative Extension. Bell is a scientist at the New Zealand Institute for Plant and Food Research and was called into action when leafroll emerged as a large issue in that country, which has 87,487 acres planted to grapevines and exports $1 bil- lion worth of wine annually. "Leafroll was seen as a real threat to our business....It delays ripening, a real concern in our cool growing areas," he said. A six-year research project started in 2009 is just ending. The study conducted area-wide and block- specific studies in the 2,500-acre Gimblett Grav- els region to develop an integrated management plan to keep virus incidence below 1%. Lee said that the vines are infected with 17 viruses, but the most common f o r m p r e s e n t i s grapevine leafroll associated virus 3 (GLRaV-3). The study set a 20% threshold for re- moving vines (rogu- ing), which means p u l l i n g t h e w h o l e block if 20% of the vines are infected. As in California, mealybugs are vectors of GLRaV-3, but the predominant mealy- bugs differ. In New Zealand, the primary mealy- bugs are longtailed (Pseudococcus longispinus) and Citrophilus mealybug (P. calceolariae). Scientists depend on both insecticides and biological control to hold populations in check. Results of mealybug management were incon- clusive. Seven of the blocks showed effective virus management, and another six were incon- clusive. Notably, the organic blocks that didn't receive pesticides showed little or no infection, but that wasn't true at other sites. "Some organic sites started with bad material." It took heavy doses of spraying to ensure contact with the mealybugs, typically 1,000 liters per hectare (2.47 acres). They sprayed once with an organophosphorus (prothiofos) compound, which is not registered for use in the United States, before budding and twice before flowering with bu- profezin (Applaud), spirotetramat (Movento) or a combination. They concluded that low mealy- bug abundance contributes to effec- tive control, but there is some evidence of tolerance to the pest. The study also looked at patterns of spreading to neighboring vines, but concluded removing only the vines that were showing symptoms was adequate. "Only 4% of the adjoining vines were infected, but 90% of the infections were in these first vines around rogued vines." Bell removed both infected vines and under- lying roots, where mealybugs can live. Overall the study with roguing infected vines plus mealybug control resulted in the number of vines infected dropping from 13% in 2010 to 2.5% in 2014. —Paul Franson New Zealand Controls Leafroll Virus By Spraying and Removing Vines NEW ZEALAND WINEGROWERS RESEARCH