UC battles Pierce’s disease

University of California Agriculture and Natural Resources has mobilized its forces against Pierce’s disease, a fatal bacterial disease of grapevines that is on the rise in California. Since 1997, between 500 and 800 acres of grapevines have been lost to Pierce’s disease in Southern California’s Temucula winegrape growing region. This year, Pierce’s disease was confirmed in a dozen vineyards east of Bakersfield.

Pierce’s disease is caused by the bacteria Xyllela fastidiosa, which clog the plant’s water conductive tissue, choking off the movement of water and nutrients from the roots to grapevine canes and leaves. Insects that have bacteria on their mouths give Pierce’s disease to grapevines when they feed on fluid in the plant xylem. In California, Xyllela fastidiosa can also cause Almond Leaf Scorch and Oleander Leaf Scorch.

Pierce’s disease is not new in California. In the late 19th century, Pierce’s disease killed thousands of grapevines in Anaheim, contributing to demise of the grape industry in Orange County. The incurable plant disease has appeared on and off ever since, particularly in “hot spots” where grapevines are planted near riparian areas or irrigated pastures that favor plants that carry the disease.

In 1989, glassy-winged sharpshooters were accidentally introduced to California. A native of the southeastern United States, GWSS has proven to be more effective at spreading Pierce’s disease than native xylem-feeding insects. According to the California Department of Food and Agriculture and surveys by county agricultural inspectors, six Southern California counties are GWSS infested: Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Ventura. The pest is well established in parts of Kern County. There are also limited infestations in isolated parts of Butte, Contra Costa, Fresno, Sacramento, Santa Barbara, and Tulare counties.

A wide variety of research programs are being conducted by UC Riverside, UC Davis, UC Berkeley, and UC Cooperative Extension scientists. In Kern County UC farm advisors are working with farmers and county, state, and federal officials to remove and destroy 572 Pierce’s disease-infected grapevines to avoid further spread of the disease. A glassy-winged sharpshooter task force in Kern and Tulare counties, chaired by UC Cooperative Extension viticulture advisor emeritus Don Luvisi, is conducting research to determine the best ways to control glassy-winged sharpshooters in citrus and grapes.

Researchers at UC Riverside are searching for natural enemies of the glassy-winged sharpshooter to release in infested areas for non-pesticide control and researching the potential use of physical barriers to prevent the glassy-winged sharpshooter from flying from field to field transferring diseases.

Scientists at UC Davis are working to identify genes in cultivated grapes and wild grape plants that have resistance to Pierce’s disease. In addition, the possibility of inoculating vines against Pierce’s disease is being studied.
At UC Berkeley, scientists are studying the ecophysiology of the bacterium Xylella fastidiosa in plants and in insect vectors.

(January 2002)

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