2000 PD Report Pierce's Disease and Its Vectors

Pierce’s disease was first recorded in Orange County in the 1880s when it killed more than 40,000 acres of young grapevines in less than five years. Known then as “California vine disease,” PD put a quick end to the expansion of winegrape production in the south part of the state.

Over the next century the disease, which is named for N.B. Pierce,^[1] reappeared occasionally. The records show several cyclical outbreaks of PD prior to the last decade, the most significant occurring in the 1940s and costing growers more than $10 million. While its symptoms were known, the cause of Pierce’s disease remained a mystery.

About 25 years ago, scientists at UC Davis linked Pierce’s disease to an unidentified bacterium. Their colleagues at UC Berkeley were able to culture the bacterium, Xylella fastidiosa, and Davis researchers found that it damaged grapevines by entering the plant’s water-conducting tissues (xylem), multiplying rapidly, and eventually clogging its critical water and nutrient transport system.

UC researchers also discovered that the disease is spread by sharpshooters, an insect related to the common leafhopper. Sharpshooters feed by piercing the xylem of plants and sucking the sap. If the plant already carries X. fastidiosa, a sharpshooter can transmit the bacterium from diseased to healthy plants. Unlike phylloxera which causes a long, slow decline in production, a vine infected by X. fastidiosa and left untreated typically dies within a year or two. During this period, the vine produces no fruit.

Pierce’s disease has reemerged recently as a vineyard problem in both Northern and Southern California winegrape growing regions. An outbreak of this lethal disease of grapes began in Napa and Sonoma counties in the 1990s and PD has since been found in Mendocino and Lake counties. The disease has cost North Coast growers an estimated $33 million and required the removal and replanting of more than 1,000 acres of vines.

^[1] Newton B. Pierce, special agent to the United States Secretary of Agriculture and California’s first professionally trained plant pathologist, is credited with identifying the disease that was later to bear his name. Pierce was able to reject many of the prevailing explanations of what caused grape disease, but never was able to find the true cause. This is ironic because his academic specialty was bacterial pathogens. Pierce published his findings in 1892 as California Vine Disease, U.S. Dept. of Agriculture, Division of Vegetable Pathology, Bulletin No. 2.