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Pinot Gris Virus Discovered in More Napa Vineyards

January 2017
by Ted Rieger

Davis, Calif.—Grapevine Pinot Gris virus (GPGV) has been detected in vineyards in 14 locations in Napa County, but not in other California vineyard locations to date, based on initial findings from a statewide survey started in 2016 and funded through an American Vineyard Foundation research grant.

These findings and an update on GPGV were presented by Dr. Maher Al Rwahnih, diagnostic and research lab director at Foundation Plant Services (FPS) at the University of California, Davis, during a day-long extension class, “Current Issues in Vineyard Health,” held Nov. 29 in Davis.

Disease symptoms associated with GPGV were first observed in vineyards in Italy’s Trentino Alto Adige region in 2003. Symptoms include chlorotic leaf mottling, leaf stunting and deformation, delayed vine growth, stunted canes and reductions in yields. There have been reported impacts on grape quality and plant growth in European vineyards as well.

GPGV has been reported in red and white wine and table grape varieties in a growing list of countries including Canada and the United States.

In 2015, Davis-based commercial testing lab Agri-Analysis reported that seven vines from four separate vineyards tested positive for GPGV in Napa Valley. This is believed to be the first reported detection of GPGV in commercial vineyards in the United States.

To date, infected vines have only been found in Napa County. The AVF survey detected GPGV in samples of Cabernet Sauvignon, Chardonnay, Sauvignon Blanc, Malbec, Merlot, Petit Verdot, Pinot Noir, Zinfandel, Viognier, Sauvignon Musque and the rootstock 1616C.

In one newly planted Napa vineyard, 100% of the vine samples tested were infected with GPGV. Al Rwahnih said this vineyard was planted with rootstock in 2014 and field budded in 2015. This strongly suggests that the vine material already had the virus when it was placed in the field.

Since much is still unknown about this virus, its detection does not necessarily mean the disease will affect vine health. In many cases, GPGV is found in vines with multiple virus infections.

Another finding from the 2016 survey was that the virus level (titer) in infected vines was highest in the early season (May and June) and decreased during the growing season.

Based on recent research in Italy, the grape erineum mite, a type of eriophyid mite found in vineyards worldwide, was shown to be a vector that can transmit GPGV to healthy grapevines in greenhouse experiments.

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