Ag Today August 18, 2017

Grapevine scourge has returned to Temecula Valley’s Wine Country

By Aaron Claverie, Riverside Press-Enterprise

The glassy-winged sharpshooter, a flying menace that devastated the Temecula Valley Wine Country in the late 1990s, has made an ominous comeback.

The insect — which carries the deadly-to-grapevines Pierce’s Disease — has been detected in area orange groves.

UC Riverside scientist Matt Daugherty, who leads the monitoring efforts in the region, said this week that his team captured more than 1,500 of the half-inch shooters last month in the groves, the largest haul since a trapping program was instituted in 2003.

“It’s certainly very scary,” he said, adding that the previous recorded high for the region was in 2008 when around 1,000 insects were detected.

In the late ’90s, the region’s growers had around 3,500 planted acres of vineyards, producing fruit that was largely shipped off to wineries in other parts of the state. That number dipped to 1,000 acres in the wake of the sharpshooter’s invasion, which left grapevines starving for water due to the injection of the bacterium the sharpshooters can carry.

The growers who survived the collapse adapted, planting new varietals that were a bit more hardy. Others sold their land to investors who started up small wineries that catered to adventurous wine lovers.

Those small wineries helped prove the viability of the region as a winemaking area and new money followed, including investment from China, turning the area into a tourist destination popular with daytrippers, wedding planners and snowbirds.

Even with Wine Country’s rebound, the total number of acres planted — 1,800 — is still only around half what it was before the collapse.

Growers have attributed the severe uptick of the sharpshooters to the winter storms that revived some citrus groves that had been fallowed during the drought. When the rains came, the water injected life into untreated trees and provided a fertile breeding ground.

“They respond positively to warmish and wet winters and springs,” Daugherty said. “It’s really plausible the big influx of rain could have kicked off new production.”

There also is speculation that the elimination of funding for an orange grove spraying program, which had been credited for keeping the insect from making the relatively short flight to the area’s vineyards, could have given the sharpshooters a new lease on life.

Daugherty said his team has not yet pinpointed the exact reason for the increase but they are actively working on it. At the same time, they are providing the region’s winegrowers and citrus farmers — who also are dealing with citrus greening disease — with data showing areas where the sharpshooter is especially vigorous. They also are testing to see if these modern sharpshooters have become immune to the pesticides that have long been used to control the population, which would be a troubling turn of events.

“Whether this is one blip or not, we don’t know,” he said.

Responding to the sharpshooter’s resurgence, the Temecula Valley Winegrowers Association’s viticulture committee is putting together a protocol for trapping and spraying and will be distributing the plan not only to its members, but non-member small growers in the area.

“We’ll also be distributing traps to anyone who would like to set them up in their vineyards,” said Krista Chaich, the association’s director of operations.

Ben Drake, a grower who vividly recalls the late 1990s infestation, said this week that the state’s decision around three years ago to cut the funding — which amounted to $5 million or so that helped cover the cost of spraying in orange groves that specifically targeted sharpshooters — was a bad call.

“Some pressure needs to be put on the county to do something about this thing,” he said. “We’re right back where we were in 1999.”

This year’s grape harvest wasn’t affected by the increase, Drake said, but it could be an issue in future years if the bugs show a resistance to the Admire-brand insecticide that has proven effective in the past.

Greg Pennyroyal, vineyard manager for Wilson Creek Winery, said it’s important to note that the large increase in sharpshooters was discovered as part of the ongoing monitoring of the area’s citrus orchards, not the vineyards.

“The uptick isn’t an imminent threat to the vineyards yet, it’s an early indicator that we may have an issue later,” he said. “It’s urgent that we act now so we can avoid catastrophic problems.”

In addition to issuing the protocol and distributing traps, the association will be conducting seminars next month to train growers how to look for Pierce’s Disease.

In the late 1990s, growers waited too long to rip out vines, he said, allowing Pierce’s Disease to flourish. Once the disease takes hold of a vine, the sharpshooter’s presence, which is always a nuisance, becomes a deadly threat because the shooter can easily spread the bacterium to neighboring vines.

“Nowadays we’re ahead of the curve; we learned our lesson,” he said.


What is it?: A bacterium, Xylella Fastidiosa, spread by glassy-winged sharpshooters that feed on infected vegetation and then inject the bacterium into the sap of nearby grapevines.

What happens?: The bacterium lives and multiplies in a plant’s xylem, eventually blocking the movement of water and killing the vine.

What can be done?: There is no known cure for Pierce’s Disease.

Is it dangerous to people?: It affects only plant physiology and the vine’s ability to produce a crop, and does not affect wine quality and or pose a health risk to wine consumers.

What other plants are affected?: There are many other important California crops and commodities threatened by Pierce’s Disease, including almonds, citrus, stone fruits, alfalfa and oleander.


Source: Wine Institute