As a leafhopper the GWSS feeds by piercing plant tissues with its proboscis, and removing plant fluids. In the process of feeding it may inoculate the plants with a bacterium called Xylella fastidiosa, which causes devastating diseases in a variety of plants, such as Pierce’s Disease of grapes or Leaf Scorch of almonds, oleander, or mulberry. It is capable of feeding on hundreds of different crop and ornamental plants, including citrus, oaks, and maples. At the time of writing there is no cure for the disease once introduced into the plant. In temperate climates there may be two generations per year, with adults active even in January and February, when they may feed on the thin stems of deciduous trees as well as on citrus or non-deciduous ornamental plants.
Given the serious problems from its role as a vector of plant diseases an effort is being made to establish a good management program. Currently no effective cultural or biological controls are known, and since the principal problem is the disease, which only a few of the insects could spread, management is difficult. In California it may still be a quarantine species, and if found should be reported to the County Department of Agriculture.