A population of glassy-winged sharpshooters -- the most feared of the insects that spread Pierce's disease, an incurable vine malady -- was discovered this week in Tulare County, in the heart of California's Central Valley, where much of the state's bulk wine is produced.
Lone glassy-winged sharpshooters have been sighted recently in Lodi, a Central Valley wine appellation, and eggs have been discovered on ornamental plant shipments as far north as Sonoma County. But this is the first incident of a full population (a colony of adults, eggs and nymphs) being discovered outside of the eight southern California counties that have previously been infested.
The colony was located in a residential area that appears to cover about 1 square mile. The bugs do not yet seem to have spread to the 11,000 acres of wine grapes in the county, which also has extensive table-grape plantings.
Since the 1930s, Tulare County has battled P.D., a bacteria-induced vine disorder that can be spread by a variety of insects. "Pierce's disease has probably been just as severe here in Tulare County as the outbreaks in Napa," said Tulare County farm advisor Bill Peacock, but the problem hasn't gotten as much attention because the region doesn't have the high profile that Napa Valley does.
Because the disease-causing bacteria is already established there, Peacock said that if "we ever get an efficient vector such as the glassy-winged sharpshooter, P.D. could easily be spread from here throughout the Central Valley." The glassy-winged sharpshooter is the farthest-flying of the carrier insects and can live on a wide variety of plants.
California and Tulare County agricultural officials are currently trying to assess the extent of the glassy-winged sharpshooter population and determine the best method of eradicating the threat.
Read past reports on Pierce's disease: