UCCE helps farmers tackle powdery mildew

In desperation, Allan and Mineca Griggs turned over a chunk of their Shasta County vineyard to University of California researchers to find a solution to their severe powdery mildew, according to a story in the Redding Record-Searchlight.

“There are not too many people willing to sacrifice a crop in their vineyard to do a trial. No one wants to jeopardize their income,” Griggs told reporter Laura Christman. “But I wanted to know an answer.”

The Griggs farm, situated at the 2,400-foot elevation and surrounded by forests, is an ideal environment for powdery mildew, but the farm is by no means alone in its struggle with the fungus. Powdery mildew is the No. 1 disease of grapes in California, according to UC Davis plant pathologist Doug Gubler, who has been studying powdery mildew for 27 years.

Gubler headed up a trial on the Griggs' farm comparing four organic treatments for powdery mildew: Kumulus (micronized sulfur), Serenade (bacterial product), JMS Stylet (horticultural oil) and Regalia (knotweed extract). Some vines were left untreated as a control. Micronized sulfur worked the best, Christman reported.

The viticulture farm advisor in Shasta County, Dan Marcum, applied the treatments to the vineyard.

“There might be better ways to make the other products do better,” Marcum said. “There’s more research to be done.”

Downy mildew and powdery mildew on a grape leaf.

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