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Vineyard mystery: how do "red leaf" diseases spread?

To fight red leaf diseases in vineyards, UC researchers know what they need to figure out: what’s the vector? How do the diseases move?

Unfortunately the latest research reveals how hard of a problem it is to solve that mystery.

“We’re still not sure how this is moving around,” said UC Cooperative specialist Kent Daane. “We’re still not sure its effect on your crop.”

So what has the latest UC research showed?Diseases spread most easily in September and October.

The diseases are a hot button issue in Sonoma and Napa, but not so much in Central Valley, Daane said.

It’s possible that alfalfa hoppers could be the vector. It is the only insect that’s been studied that has been shown to transmit the diseases.

“If you do find any red leaf vines, contact your farm advisor, contact someone here at Fresno State and get that material tested,” he told growers during a presentation at Fresno State.“ Our biggest worry is… areas in southern Napa, near Carneros…we’ve got so many vineyards surrounded by grasslands, we don’t know what insects are moving in and out,” Daane said.

Daane’s research project shows that wild grape is a reservoir of red blotch type viruses.

A handful of insects, along with alfalfa hopper, have tested positive to carry the viruses.

“Rapid spread of this virus by an insect in commercial vineyards seems unlikely,” said a summary of Daane’s research. “Current movement is dependent on pathogen and three-cornered alfalfa hopper abundance in or near vineyards.”

Growers should keep an eye out for further results as the team continues its research.

Eliot Caroom

Eliot wrote about AgTech, aerial images, and other farming topics for Ceres Imaging. His past work includes local newspaper reporting, oil market news, and covering sustainable investing.

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