Pierce’s Disease On The Rise
February 18, 2016 Pierce’s disease hit hard in California’s Sonoma and Napa counties this past year.
According to Rhonda Smith, University of California Cooperative Extension viticulture farm advisor, even sites that are typical “hot spots” for the disease lost hundreds of vines more than they have in past years.
“In some of those vineyards, the disease also appeared in areas which it had never previously occurred,” Smith says. “In addition, some growers who had vineyard blocks that normally experience little to no Pierce’s disease lost a significant number of vines in 2015.”
The losses were so significant that many growers who wanted to replace dead vines weren’t able to due to nurseries being unable to meet vine demand.
Although the exact cause of the uptick in Pierce’s disease is unknown, there are a number of hypotheses, which will be investigated over the next three years, Smith says.
One theory is that the population of blue-green sharpshooters, one of the pests that carry the Xylella fastidiosa pathogen that causes Pierce’s disease, has increased.
Warm winters might be fueling the problem. Smith says vectors can’t normally acquire X. fastidiosa in early spring, but warmer winter weather could be lengthening the window of time when insects can acquire the pathogen from vines. In addition, higher temperatures may be preventing vines from recovering from infections that occur later in the summer. “We may continue to see elevated incidence of Pierce’s disease in North Coast vineyards if warm winter temperatures persist,” she says.
Minimize The Risk Of Infection
To reduce the number of infected vines, Smith suggests reducing the number of sharpshooters entering the vineyard from neighboring vegetation in early spring. “In Pierce’s disease hot spots, avoid planting susceptible cultivars such as Pinot Noir and Chardonnay,” she adds. “Once vines have severe Pierce’s disease symptoms for more than one year, they are chronically infected and will not recover. Those vines should be removed.”
Check out the UC IPM Grape Pest Management Guidelines for more information on Pierce’s disease and sharpshooter management.
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