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Pierce's disease monitoring continues with new tool

University of California Cooperative Extension advisors are testing a new tool to help farmers keep Pierce’s disease of grapes at bay. The quick-test device can be used in the field and promises accurate, same-day analysis of vines suspected of being infected with Pierce’s disease.

"If this diagnostic tool proves to be effective, we can identify a vine with PD symptoms in the morning, and pull it out that afternoon with confidence that it was diseased," said Jennifer Hashim, the viticulture farm advisor in Kern County who is leading the county’s PD monitoring program.

Currently, scientists and farmers take samples of vines showing PD symptoms and ship them to labs for analysis. The No. 1 drawback is the time it takes to send out samples and wait for lab results – anywhere from three days to two weeks, depending on the work load at the lab.

The results generated by the new device will be compared to the old standard in the coming months as the 2004 Kern County PD monitoring program gets under way beginning at the end of August and continuing through mid-November. Hashim and her staff will re-examine more than 200 vineyards that were surveyed in 2002 and 2003 to track the spread of Pierce’s disease. The 200 vineyards – covering about 4,000 acres – represent roughly 5 percent of the total bearing grape acreage in Kern County.

"I’m interested to see what happens this year," Hashim said.

The incidence of Pierce’s disease was high in 2001 and 2002, but decreased sharply in 2003. Hashim said she is hopeful 2004 results will show a continued downward trend.

"The 2004 growing season was marked by a low level of glassy-winged sharpshooters and growers have been very vigilant about pulling out vines that come back positive for PD," she said.

Pierce’s disease of grapes is caused by the bacterium Xylella fastidiosa. The bacteria are spread by insects that feed on infected plants – including weeds, native plants and agricultural crops – and then feed on grapevines. They also can be spread from vine to vine by glassy-winged sharpshooters (GWSS). Pierce’s disease has occasionally killed vines as long as grapes have been cultivated in Kern County; however, introduction of GWSS eight years ago caused a spike in Pierce’s disease infections.

A task force formed in 2001 and coordinated by UC Cooperative Extension farm advisor emeritus Don Luvisi has been instrumental in reducing glassy-winged sharpshooter numbers and limiting the spread of Pierce’s disease.

The task force meets from 10 a.m. to 12 noon Sept. 15 at the Kern County Agricultural Commissioner’s office, 1001 S. Mt. Vernon Avenue in Bakersfield. The meeting includes updates from areawide task force coordinators for Tulare and Kern counties, a statewide update from California Department of Food and Agriculture, a U.S. Department of Agriculture report, a biocontrol update and information on bulk grape and citrus movement in Kern and Tulare counties.

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