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November 13, 2001  Pierce's disease confirmed in Kern County vineyards
UC and other officials are working with farmers to remove and destroy the approximately 600 infected vines to avoid further spread of the incurable and fatal disease. In addition, Hashim is conducting educational programs, consulting with farmers, and distributing materials on Pierce's disease identification and management strategies.
"We will work with growers to develop field monitoring programs and control strategies," Hashim said. "Growers should carefully watch their vines and submit samples of vines that exhibit Pierce's disease symptoms to CDFA (California Department of Food and Agriculture) for analysis."
Pierce's disease is caused by the bacterium Xylella fastidiosa, which clogs 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 the bacteria on their mouths transmit Pierce's disease to grapevines when they feed on fluid in the plant xylem. In California, Xylella fastidiosa can also cause Almond Leaf Scorch and Oleander Leaf Scorch.
Pierce's disease is spread in Kern County by native sharpshooters and the glassy-winged sharpshooter, a pest introduced to the area about five years ago. Sixteen infected grapevines identified in summer 2000 in one Kern County vineyard were removed and destroyed last year.
"Our 2001 survey results indicate that glassy-winged sharpshooters are very effective transmitters of Pierce's disease," Hashim said. "Growers should quickly remove any vines that are diseased. That's the best way to minimize the sharpshooters' opportunities to acquire the bacterium and pass it on to more vines."
Hashim's survey work in grapevines was conducted in conjunction with the General Beale Road Pilot Project, a collaborative research program of the Glassy-Winged Sharpshooter Task Force of Kern and Tulare Counties. Project participants are the Agricultural Commissioner offices of Kern and Tulare counties, California Department of Food and Agriculture, University of California Cooperative Extension, USDA Animal Plant Health Inspection Service, and USDA Agricultural Research Service.
Hashim and a staff of CDFA and California Conservation Corps workers began their vineyard survey in early April, focusing on 20 rows of Flame Seedless grapes adjacent to where diseased vines were pulled out in 2000. Although some vines showed severely delayed growth, incidence of Pierce's disease could not be determined because early season diagnostic tests have not been developed.
Surveying continued in June in the Flame Seedless vineyard and a nearby Red Globe vineyard. Crews took 400 samples from vines that exhibited visual symptoms of Pierce's disease - stunted growth, leaf scorch, and persistent petioles, leaf stems still attached to the cane after the leaf has dropped off. Of the samples taken, 308 were positive for Pierce's disease.
In August the survey expanded to 400 acres within a two- to three-mile radius of the
General Beale Road Pilot Project. The focus was on Red Globe, a table grape variety considered to be particularly susceptible to Pierce's disease. An additional 11 vineyards ranging in size from three to 40 acres were surveyed and 500 more samples were collected. Of those, all but one vineyard was confirmed to have vines with Pierce's disease. A total of 264 vines tested positive.
"Pierce's disease is more widespread in the project area than we originally thought," Hashim said. "We don't know how many more diseased vines are present in non-surveyed vineyards within and outside the pilot project area."
In the coming year, Hashim will survey selected vineyards to estimate the incidence of Pierce's disease in glassy-winged sharpshooter-infested regions, an area that encompasses 35,000 acres of grapes in eastern and southern Kern County.
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