Agricultural Commissioner / Sealer of Weights & Measure


Pierce's disease has existed in California since it was first identified in the late 1880s. It is blamed for the eventual destruction of winegrape industries that flourished in Southern California until the late 19th century. The disease destroyed 40,000 acres of grapes near Anaheim in the 1880s. Pierce's disease is the most prominent disease caused by the bacterium Xylella fastidiosa, which attacks the plant's xylem, or water-conducting tissues and eventually chokes of the flow of water and nutrients within the plant.

Currently, Pierce's disease exists in Napa, Sonoma and Mendocino winegrape regions, spread from the less aggressive blue-green sharpshooter. The disease will eventually kill or render unproductive vines or other plants within two to three years. There are no effective treatments at this time.

Some strains of the bacterium that are not yet established in California might now spread rapidly if they are ever introduced into the state. These strains include those causing serious disease of citrus in South America and important diseases such as almond leaf scorch, alfalfa dwarf and oleander leaf scorch.

The glassy-winged sharpshooter is a new mobile insect vector with a variety of food sources, spreading a disease that threatens the state's grape industry, as well as other major agricultural crops. There is concern that with some genetic changes, the bacterium could manifest itself as citrus x disease, which has destroyed 60 million citrus trees in Brazil. The sharpshooter worsens Pierce's disease because it:
  • Increases the numbers of vectors
  • Moves faster and farther into vineyards compared to the blue-green sharpshooter
  • Has a much wider range of host plants
  • Feeds on the larger (basal) stems of plants, leading to exponential disease increase
  • Has breeding habits and the plants differ from traditional sources of Piece's disease vectors; and,/li>
  • There is no effective treatment for it.
Without an effective treatment, scientists fear the glassy-winged sharpshooter will spread throughout the San Joaquin Valley, threatening nearly 800,000 acres of wine, table and raisin grapes - more than 70 percent of the state's vineyards - with Pierce's disease.