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PIERCE'S
DISEASE
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,
-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. |
