GWSS Numbers Spike in Temecula: Grower Complacency Seen as a Factor
The number of Glassy-Winged Sharpshooters counted in Temecula, California during 2008 has been rising and is nearing levels not seen since 2001--indication that the area could potentially see a new wave of Pierce's Disease, according to Nick Toscano, a senior entomologist with the University of California, Riverside.
PD destroyed about 40 percent of the vineyards in the Temecula area prior to 2001 and millions of dollars have since been spent on research and containment, as the GWSS and PD are considered a threat to vineyards throughout California. The GWSS is the bug that spreads the lethal vineyard disease.
A number of factors are at play, including unusually hot weather, but a key reason for the recent increase in the GWSS count is grower complacency, Toscano told Wine Business Insider.
Neonicotinoid insecticides with brand names such as AdmirePro, Alias, Platinum and Venom have been shown to be effective for GWSS control and are typically applied through irrigation systems. Not all growers are treating their vineyards these days, though, possibly due to the cost: roughly $125 to $150 per acre per season.
Though the chemicals are considered safe, growers are required to notify the county when they've treated their vineyards. Working with County Ag Commissioners, Toscano was able to map out the area and has determined that 40 percent of the vineyards in Temecula are not being treated.
"We're concerned about grapegrowers," he said. "It's like taking a flu shot," Toscano said of the insecticide treatments. "You have to do it every year."
GWSS populations and development are largely temperature-driven. Toscano believes there have been three generations of GWSS and maybe a fourth. He said additional reasons for the high GWSS populations in Temecula are: no rain after January; mild winter and temperatures close to 100 degrees for a couple of weeks in June; urbanization, as treatments of citrus have been limited because of homes built in citrus groves without proper irrigation systems to split off insecticide treatments; and ornamental host plants used by homeowners. Additionally, riparian areas can't be treated.
"The implication is that within two or three years, growers might find they have high rates of PD in their vineyards," Toscano said. "We could revisit what happened prior to 2001, when they lost over 40 percent of their vineyards in Temecula. We're already seeing signs of this in areas that haven't been treated since."
In other news, three adult GWSS were found in traps in the Capitol area of San Jose, Santa Clara County on October 30, prompting a rapid-response survey of the area. The survey has since found 103 additional live specimens on 39 properties. The finds are outside of the county's existing infested area. Survey activities are continuing.