Temecula, Calif. Braces for Return of the Glassy-winged Sharpshooter

Temecula vineyard With Ripe Grape Clusters Ready For Harvest.

Glassy-winged sharpshooter populations are spiking in the Temecula Valley, the Southern California wine region that was ravaged by the Pierce’s disease-spreading insect nearly 20 years ago.

When more than 1,500 of the low-flying sharpshooters were caught in nearby orange groves in July, the Riverside County viticultural community immediately began collaborating to ensure that the scourge does not spread like before, when only 1,000 of the original 3,500 acres were left standing.

“What we’ve learned from the last go-around is that you need to educate all vineyard operators early and thoroughly to make sure that they know how to monitor this and, if they’re affected, what their treatment options are,” said Greg Pennyroyal, viticulturist for Wilson Creek Winery & Vineyards and a professor of viticulture at Mt. San Jacinto College.

In addition to vigilance by the Temecula Valley Winegrowers Association, Pennyroyal is spreading monitoring and treatment protocols through Small Winegrowers of Temecula, an organization, which has about 160 members who each have less than 20  acres of grapes who have anywhere from six vines to 20 acres of grapes.

Economic Cause And Effect

A map of the areas that were infested by Glassy-winged Sharpshooter.
Distribution map via the Center for Invasive Species Research, University of California, Riverside

Why the sharpshooter, which is not native to California, is back en masse after 15 years is unclear. But three years ago, the state slashed the program that paid for vineyard monitoring and pesticides on citrus orchards to reduce sharpshooter populations. Now, monitoring only occurs in citrus groves, where the bug overwinters and breeds, but does not cause such devastation.

“I don’t know if there is enough evidence to say that it’s causal,” Pennyroyal said. “But when you stop monitoring in vineyards and stop treatment in orchards and you suddenly see the bug population spike, there’s a strong logical conclusion that those two might be connected.”

Pierce’s disease is expensive for grape growers. The region  had 3,500 acres of vines in the ‘90s before the sharpshooters infestation cut that acreage to 1,000. It has not fully recovered. Today, there are nearly 2,000 acres, much of them planted with varieties more suitable to the warm climate. Temecula vintners do not want to start over again, so they are being extremely proactive.

“Get burned once, and you learn,” Pennyroyal said. “Get burned twice, and you’re just stupid.”

Published on August 25, 2017
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