The Glassy-winged sharpshooter (GWSS) (Homalodisca coagulata) is a serious pest in California. This insect was first observed in California in 1990 and is now found throughout Southern California and portions of the San Joaquin Valley. It is a particular threat to vineyards due to its ability to spread Xylella fastidiosa, the bacterium that causes Pierce's disease. Pierce's disease kills grapevines and there are no effective treatments for it. The Glassy-winged sharpshooter also spreads other diseases to a variety of agricultural and ornamental plants.

To prevent the introduction of this leafhopper into Marin County, staff have inspected all incoming nursery plant shipments from infested California counties. A total of 1,345 shipments were inspected for GWSS in 2008. Detection traps are also monitored for the Homopterous pest.