A SPECIAL GROWERS’ REPORT OF AG ALERT ® C A L I F O R N I A Trees & Vines ®
Grapevines are vulnerable to two viral diseases, leafroll and red blotch, that can be carried into vineyards by insects. Both diseases can reduce yields and brix, and affect the quality of wine made from the grapes.
Advisors describe ways to manage vine diseases ByBob Johnson
vineyard is infected, and remove the block if it is more. “If the disease is above 30%, we recommend removing the block,” Fuchs said. “I do not recommendmanaging populations of the three-cornered alfalfa hopper.” University of CaliforniaCooperative Extension integratedpestmanagement special- ist Kent Daane told the seminar control of the vine mealybug is extremely important inmanaging leafroll virus. Daane said there has been “an explosion” of vine mealybugs since 2008, and it has become “the most important insect pest in California vineyards.” “Except as a vector, these mealybugs would just be nuisances,” he said. “But they havemore eggs andmore generations than othermealybugs. You can have six or seven generations in the Central Valley and three to five near the coast, and they only lose the ability to carry the leafroll pathogen when they molt.” It takes the vine mealybug only an hour of feeding on an infected vine to pick up leafroll virus, and then an hour of feeding to transmit it to a clean vine. Daane has led in the development of an areawide program for controlling vine mealybugs through a combination of pheromone mating disruption and insecticide applications in hot spots.
Winegrape researchers are piecing together strategies for identifying andmanaging two major viral diseases—leafroll and red blotch—that can look a lot alike but have different insect vectors and preferred control strategies. Both leafroll and red blotch significantly reduce yields and brix, and damage color and other quality measurements of wine. Specialists say the more recently discovered red blotch appears to have inefficient insect vectors, which means it spreads less aggressively than leafroll within a block or to nearby vineyards. “The three-cornered alfalfa hopper is the vector,” said Marc Fuchs, professor of plant pathology at Cornell University. “Unlike themealybug that transmits leafroll, the three-cornered alfalfa hopper is not a pest of grapes and is not capable of reproducing on grapes.” Fuchs made his remarks during the Virtual Sustainable Ag Expo and International Sustainable Winegrowing Summit. “There is only one known vector for red blotch,” he said. “There are other candidates, but none of them are grape pests. Grapes are not the preferred host of the three-cor- nered alfalfa hopper; legumes are the preferred hosts. Watch your cover crop varieties.” With red blotch, the management recommendation is to rogue if 30% or less of the
See VINES, Page 8
March 24, 2021 Ag Alert 7
Powered by FlippingBook