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Pierce's disease (P.D.)

A bacterial disease that attacks and kills grapevines and other crops including almonds, citrus, and stone fruits. It’s named for Newton Pierce, a plant pathologist who investigated the first outbreak of the disease in California vineyards in the late nineteenth century. Pierce’s disease is a bacterium (Xylella fastidiosa) that lives and multiplies in a plant’s xylem, its pipelike water-transportation system. . It takes a year for symptoms of the disease to begin appearing. Within 2 to 3 years from infection, bacteria levels become so concentrated that they clog the plant’s vascular system, preventing transfer of moisture and nutrients and killing the plant. Infected vines exhibit stunted growth, discolored, underdeveloped leaves, and dried, shriveled grapes. A vine killed by the disease is withered and black. California winemakers have been battling this fatal disease on and off for well over a century. It decimated southern P California vineyards in the 1880s, struck again in the 1930s and 1940s, and returned in full force at the approach of the new century. Normally, Pierce’s disease is transmitted by the blue-green sharpshooter, a tiny leafhopper that feeds on plant juices. The disease is spread by the insect’s mouth, which transfers bacteria from an infected grapevine to a healthy one. Although the blue-green sharpshooter has long been a bane to the California wine industry, it’s an insect that breeds and does most of its damage within 100 yards of rivers and streams, which meant that there was some degree of control. All that changed in 1989, however, when nursery stock from the southern United States carried an uninvited and much more powerful predator—the glassy-winged sharpshooter. Most leafhoppers are weak flyers, but the glassy-winged sharpshooter is the exception. Called the “pterodactyl of sharpshooters,” this insect is an aggressive flyer with a voracious appetite; it has spread Pierce’s disease with astonishing speed. At this writing, most of the area infested by the glassy-winged sharpshooter is in Southern California and Southern San Joaquin Valley. However, the fact that there is currently no known cure for this dreaded disease has California winemakers worried that it could potentially wipe out the entire industry. For this reason, hundreds of people are frantically searching for an answer, and a statewide program has been initiated to find either a cure for or a way to control Pierce’s disease. Currently, the best hope for controlling the glassy-winged sharpshooter is through detection and inspection and through targeted vineyard ground spraying in heavily infested areas. Biocontrol methods are introducing parasitic wasps that lay eggs in the glassy-winged sharpshooter eggs, thereby killing their host. Scientists are trying to decipher the disease’s DNA in order to develop a way to kill the bacterium without harming the vine. Grapevines are being bred in hopes of identifying disease-resistant characteristics. A “chemotherapy” method using natural zinc, manganese, copper, and iron compounds is being tested with the goal of inhibiting in vitro growth of Pierce’s disease. Unfortunately, nothing has helped, and the dreaded Pierce’s disease continues to threaten California’s wine industry. About the only good news about this disease is that it doesn’t affect wine quality or pose a health risk to humans. Furthermore, it seems to thrive only in southern U.S. climes, from Florida to California, and hasn’t been seen north of California or the equivalent latitude. All of which is little consolation to VINTERS who are in jeopardy of losing their livelihoods. See also DISEASES, VINEYARD.
Related Links: leaf-roll virus, bitter rot, Viognier, black rot
© Copyright Barron's Educational Services, Inc.
1995 based on THE WINE LOVER'S COMPANION,
by Ron Herbst and Sharon Tyler Herbst.

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