The Temecula Wine Country where GWSS has all but decimated wine grapes is only two driving hours away from where America gets it first table grapes in the spring. However, the 14,000 acres of table grapes in the southern end of Coachella Valley have yet to be touched by GWSS or the deadly malady it vectors, Pierce’s Disease.
The insect is there, albeit in much smaller numbers than Temecula, and the disease is there, but Robert Bianco, co-owner of Anthony Vineyards in Coachella and president of the California Desert Grape League is perplexed to understand the good fortune of the two dozen growers who make up the region’s $150 million early season table grape deal.
It could be the stifling summer heat of the southern desert valley where temperatures of 120 degrees are not uncommon, said Bianco. GWSS may not be able to survive the heat in large numbers. Others think it could be the use of Admire to control another recent troublesome pest, the grape mealy bug. Admire is very effective against GWSS, and growers could have been unknowingly controlling GWSS while keeping the mealy bug in check.
"We have the glassy-winged sharpshooter. However, we have not detected the disease in our vineyards and don’t know for sure why. What we do know is that we have been very lucky," said Bianco.
But the table grape growers know luck is what you take to local casinos. It won’t stop GWSS and Pierce’s Disease. That is why they are fully supporting the research and trapping efforts of their new University of California Cooperative Extension viticulture farm advisor, Carmen Gispert, a University of California, Riverside doctoral candidate who has researched GWSS and PD.
Since April 1 Gispert, who is based in Indio, Calif., has been weekly monitoring 190 GWSS traps in the Coachella Valley in a $92,000 advance-warning program for GWSS and Pierce’s Disease
She also has been sampling vineyards and has examined 7,500 vines for possible Pierce’s Disease. She sent 180 suspect samples to a lab, but none came back PD positive.
"It can be very difficult to detect Pierce’s Diseases since the reservoir is low," she said. "So far, however, we have not found the disease in vineyards."
"We have been very impressed with the work Carmen has been doing here," said Bianco, who described her efforts as "good business due diligence. We know what can happen when Pierce’s Disease gets into a vineyard with sharpshooter high numbers. All we have to do is look at Temecula and see what they are facing in Southern Kern County in the San Joaquin Valley.
"Carmen is the best we have had here and is working to give us the research answers we need right now. We are very confident that she can detect any problems before they become too widespread," said Bianco.
And growers backed that opinion with cash. Gispert received $30,000 from valley grape growers to begin her research earlier in the year when research grant money was slow coming in.
Gispert said traps typically catch one or two GWSS each week. Some, however, have had much higher counts. She traps both in agricultural areas and in urban areas where there is a wide range of GWSS hosts.
Pierce’s Disease is present in the valley in many plants. Several years ago the Smoke Tree Sharpshooter vectored Pierce’s Disease along roadways in Southern California and decimated oleanders.
Gispert also is monitoring GWSS movement from citrus to grapevines, trapping in 50-, 100- and 500-foot intervals between citrus and grapes.
"A lot of the grape growers also are citrus producers, and that makes cooperation much easier here," said Bianco.
Citrus, which is not affected by GWSS or Pierce’s Disease, was pinpointed early on as the major breeding ground for sharpshooters in the Temecula area. GWSS has been in Southern California citrus in high numbers since the early 1990s. Temecula area citrus has been treated with insecticides to try and ward off GWSS invasions.
Gispert also works in the Temecula area and has seen first hand the devastation of Pierce’s Disease. Unfortunately, some of the remedial efforts to control the disease, like cutting off diseased cordons, have proven futile.
Once a vine is infected with Pierce’s Disease, there is little a grower can do to prevent it from dying eventually — even if he cuts off visually infected cordons in an attempt to save the trunk of the vine, she said.
Coachella Valley table grape producers do not want to wait for that slow death.
"It is tough enough to make it in the early season table grape deal with competition from Mexico and Chile without having to deal with glassy-winged sharpshooter," said Bianco.
"So far we have been very fortunate, and we want to keep it that way with Carmen’s help," said Bianco.