Vines Continued from Page 7
diseasewill quickly spread fromdiseased plants throughout the vineyard. “We have to be careful and vigilant when we select planting material ,” Fuchs said. One of the problems in managing the diseases, he said, is it is not always obvi- ous which is present. “We get a lot of questions about symp- tom and vector ID for leafroll and red blotch,” Fuchs said. “Blotch and leafroll symptoms are frequently confused with each other and (with) other vine diseases and conditions.” On red grape varieties, he said, lea- froll can redden leaves, except for the veins; on white varieties, the symptoms “are less conspicuous.” Red blotch caus- es blotchy patches that eventually co- alesce, he said; on white varieties, the patches are chlorotic. “Red blotch diagnosis is a challenge,” Fuchs said, “because this is a newdisease forwhichwe don’t have the level of famil- iarity that we have with leafroll.” For diagnostic help, UC Cooperative Extension farm advisor Monica Cooper is working with a group to develop a smartphone app that will let a grower photograph stressed vines and learn if the disease is leafroll or red blotch. ( Bo b J o hn s o n i s a r e p o r t e r i n Sacramento. He may be contacted at bjohn11135@gmail.com.)
A UC Riverside researcher identified and synthesizedmealybug pheromones, he said, and Sutera has released a spray- able formulation researchers used to achieve 50% to 60% reductions in leafroll virus crop damage. “We got i t to work,” Daane said. “Mating disruptionworks best when you keep the pressure on. You do it year after year, along with insecticides.” He said mating disruption works best with low populations. “The hope is once you get the popula- tiondown in the thirdand fourthyear, you can back off on the insecticides,” he said. Daane is working on a f ive-year, areawide vine mealybug control proj- ect in 150 acres of neighboring Napa County vineyards. “You might have one grower who is applying all the controls and has no mealybugs or leafroll virus, but he has neighbors who do,” he said. “Can we come up with a program that gives con- trol for everyone?” The approach that looks promising, he said, is for all the vineyards in the area to use pheromones, then develop addi- tional controlmeasures formealybug hot spots within the area. “When we were using pheromones to identify growers about hot spots,
To protect winegrapes and vineyards from the insect that carries leafroll virus, a University of California specialist has undertaken a five-year, areawide control project in Napa County.
bug population has to be reduced.” Hesaidtheapproachhasbeenusedsuc- cessfully inSouthAfricaandNewZealand. Fuchs also recommended thinking on the landscape level with both viruses, because they are widely hosted by wild grapes, especially near riparian areas. “There is little doubt in my mind that wild grapes in Northern California are reservoirs of the redblotch virus,” he said. “Wild grapes in Northern California are also heavily infected with leafroll virus.” Management for both diseases begins with planting clean stock, he said, or the
they were applying pesticides and re- ducing the populations,” Daane said. “When we stopped notifying them, the applications went down and the popu- lations increased.” Because the vine mealybug is such an efficient vector, Fuchs said a leafrollman- agement programmust include control of the pest. “Spread management for leafroll in- volves both the virus supply and vector abundance,” he said. “If either the virus or the vector is low, the rate of spreadwill be low. We have to diminish the number of infectedvines, and similarly themealy-
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8 Ag Alert March 24, 2021
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