Are glassy-winged sharpshooters—the leafhopper that carries the lethal Pierce's disease in grapes—making a comeback this year in California?


Some insect experts say the answer is yes, based on the number of insects they've caught in traps early this year.


Nick Toscano, an entomologist with the University of California, Riverside, says,"I have not seen GWSS trap counts this high in January since the Temecula GWSS area-wide program was initiated in 2000.

Citrus groves with high GWSS catches have been mapped, and treatments are planned to begin in mid-April to get a jump on the populations."


Toscano advises vineyard owners and managers to treat their vineyards with a systematic neonicotinoid, such as AdmirePro or Alias, by mid-May to avoid the possibility of GWSS spreading the Pierce's disease bacterium in their vineyards.


Pierce's disease, caused by the bacterium Xylella fastidiosa, is deadly to grapevines but harmless to humans.


Elsewhere, though, glassy-winged sharpshooter populations were lower in 2008 than in previous years.


Beth Stone-Smith with the U.S. Department of Agriculture manages the GWSS area-wide program in Bakersfield.


"Our numbers are very low thanks to a regular treatment program," she says. "Our fall foliar treatments in 2007, followed up with imidacloprid treatments in 2008, have helped us to sustain low levels of GWSS overall. It underlines the importance of regular treatments."


For 2009, Stone-Smith plans to continue monitoring population levels and treat when necessary. Such actions are designed to continue to suppress sharpshooters in Tulare County and keep them from moving further north.