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The grapevine red blotch virus causes red veins and blotches in grape leaves, causing fruit to be smaller and ripen more slowly with muted sugars and colors, which has an effect on wine quality.

Researchers grapple with grape vine diseases

UC develops new varieties resistant to Pierce’s disease, but red blotch, other pests and viruses a concern.

University of California, Davis viticulturist Dr. Andrew Walker and his research team announced success in developing five new grape varieties proven resistant to Pierce’s disease — two blancs and three noirs.

Walker told AgNet West Radio Network: “We went through thousands of seedlings over 15 years of crossings and ten of those years of grow-outs and tasting evaluations to be convinced they were useful (because taste was a critical factor in determining the viability of the new varieties).”

The grape breeding research was supported by $30 million in funding from the Pierce’s Disease and Glassy-Winged Sharpshooter Board.

California wine grape growers will vote this spring on extending the PD/GWSS Assessment effort for another five years (until March 2026). Those assessment funds go to efforts to find solutions to PD, GWSS, and additional designated pests and diseases of wine grapes.

The last grower referendum resulted in over 80% authorizing continuation of the wine grape assessment. Ballots to eligible growers (those who paid the assessment on grapes crushed during the 2019 harvest) will be ready in March or April. At least 40% of eligible growers must cast ballots for the referendum to be valid.

It’s a normal part of working conditions, but various pests and viruses remain of concern in 2020, like grapevine red blotch disease, a major threat to the $162 billion domestic grape industry.

Red blotch disease

A $3 million USDA-NIFA-funded collaborative effort to study the disease is led by cooperative extension specialist Anita Oberholster of the UC, Davis Viticulture and Enology Department with other researchers at UC, Berkeley and Oregon State University.

“The disease, caused by grapevine red blotch virus (GRBV), is an urgent problem and this research project to study its ecobiology, impact, and management in California and Oregon vineyards is needed to bridge knowledge gaps and generate strategies to manage the problem and its effects on wine quality,” she said.

“We will work to reduce the rapid spread of the disease in key wine production areas and determine the impact on all facets of the wine grape industry from growers and nurseries to wineries and regulatory agencies.”

The virus causes red veins and blotches in grape leaves, causing fruit to be smaller and ripen more slowly with muted sugars and colors, which has an effect on wine quality.

Red Blotch disease was first discovered in the UC, Davis Oakville research station in 2007, finally identified in 2012, and in 2016, the three-cornered alfalfa hopper was listed as a vector — although perhaps not the only one.

The disease has been detected not only on the West Coast, in California and Oregon, but also on the East Coast in New York. The cause of the disease and recommended ways to manage it remain unknown with the only current treatment being to remove the entire vine.

First year goal of the study will focus on developing a survey to determine the prevalence and spread of GRBV in some of the major grape production areas in the two Western states as well as potential viticulture practices to mitigate its impact on infected grapevines.

“Any viticulture practices showing positive impacts on fruit composition will be investigated further with subsequent winemaking in 2020 along with a study of cost-effective GRBV diagnostic tools,” Oberholster noted.

For more news on pests, disease management and other issues affecting vineyards, subscribe to the bi-monthly newsletter The Grape Line.

TAGS: Crop Disease
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