A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines ®
The Western grape leafhopper, inset, is a persistent challenge for vineyards, with pest populations causing defoliation and economic loss- es. But growing habitat near vines, such as coyote brush, above, can harbor predatory enemies of the leafhopper that parasitize its eggs.
Photo/University of California, Riverside
Grape growers, researchers target leafhopper pest By Dennis Pollock Fritz Helzer is no stranger to the Western grape leafhopper, a notorius pest for California vineyards since the 1870s.
Houston Wilson of UC Riverside. The meeting was co-hosted by the university and the San Joaquin Valley Winegrowers Association. The experts spoke on management of the leafhopper to prevent yield loss, reduced grape quality, photosynthesis disruption and leaf burn. Wilson favors deploying a counter-offensive against the leafhopper. His weapon of choice is habitat that can harbor enemies of the vineyard pest that parasitize its eggs. Leafhoppers overwinter as adults and have two or three generations a year on the coast and three to five generations in the San Joaquin Valley. They have a wide range of predators including soldier beetles, green lacewings, big-eyed bugs, brown lacewings, lady-bird beetle, damsel bug, minute pirate bug, spiders and hover flies. Researchers are studying natural habitat for overwintering parasitoids. That includes French prune, alder, blackberry, ceanothus, coyote brush, manzanita and willow. They are also looking at gardens and hedgerows with plantings of apple, catmint, ceanothus, mint, pear, roses and sage. But Wilson said there can be a challenge if there is a small strip of habitat neigh- boring a large vineyard. Parasitoids that overwinter can dramatically increase their population during the summer, and then overwhelm and parasitize all hosts on that strip of habitat, wiping out the population of those alternative hosts that are not a pest.
He knows a lot about the parasitoids in the genus Anagrus that parasitize it. He is also familiar with the two new generations of leafhoppers that came to California in the 1980s: the Virginia creeper and the variegated leafhopper. But Helzer, a manager with Mesa Vineyard Management in the San Luis Obispo County community of Templeton, never stops seeking new ideas to manage the leaf- hopper and similar pests. That’s because their populations can cause defoliation in vineyards and economic losses for growers—and Helzer said he wants to be on top of the threat. So he found it worthwhile to make the two-hour drive between Templeton and the Kearney Agricultural and Extension Center in Parlier for a session on how to tame the leafhopper. “We get reinforcement on a lot of information,” Helzer said. Researchers say leafhoppers can still reach dangerous population levels in some areas of the Sierra Nevada foothills and the western Central Valley. Grapes are a billion-dollar crop in Fresno County, where Helzer turned out to hear from speakers, including entomologists Kent Daane of the University of California and
See LEAFHOPPER, Page 8
June 8, 2022 Ag Alert 7
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