CaptureCalifornia winegrape growers with losses due to grapevine red blotch-associated virus (GRBaV), the causative agent of red blotch disease, may be eligible for financial assistance for vine replacement from the U.S. Department of Agriculture’s (USDA) Tree Assistance Program (TAP). The 2014 Farm Bill made TAP a permanent disaster program to provide financial assistance for qualifying growers to replant or rehabilitate eligible trees, bushes and vines damaged by natural disasters. TAP is administered by the USDA Farm Service Agency (FSA).

Marianne Morton, FSA county executive director for Napa, Solano and Yolo counties said the program will be in place at least until 2018, when the next Farm Bill is scheduled for renewal by Congress. Morton emphasized that FSA will accept an application from anyone, and said, “We will look at every application on a case by case basis.”


This article was originally published by the California Association of Winegrape Growers (CAWG) in The Crush newsletter (July, 2015). Click HERE to view the original newsletter.


Red blotch symptoms found in a Lodi vineyard.[/caption]When an application is received, FSA will send someone to inspect the vineyard for visual disease symptoms on the vines. Visual indicators may include reddening of the underside secondary/tertiary leaf veins and red blotches on leaves in red varieties. In white varieties, indicators may include very pale yellow blotches and irregular chlorosis on leaves.

However, a claim of loss due to GRBaV must be verified by the presence of the virus based on commercial laboratory testing through polymerase chain reaction (PCR) analysis. Program eligibility documents provided by FSA state that a minimum of 10 symptomatic vines must be tested from each block claimed to be infected. This sampling, coupled with visual indicators identifiable to the FSA representative, will be used to determine the extent of damage. The FSA representative must visually inspect the vineyard prior to vine removal.


“If you think you’re having a problem with red blotch, give your FSA office a call.” – Tom Slater, USDA FSA



Red blotch symptoms identified in a Lodi vineyard.

Morton listed the following program assistance parameters:

  • 500 acres is the maximum annual amount on which a producer may receive assistance.
  • The first 15 percent of loss is not covered.
  • Maximum payment rates: $4/vine replacement, $2/vine planting, $500/acre site preparation.

The grower is required to replace eligible vines within 12 months from the date the application is approved. Following vine replant, an FSA inspector will again visit the vineyard to verify that eligible vines were replaced. Morton noted that FSA has received applications and has approved some payments already.

CAWG member Tom Slater of Slater Farms in Clarksburg, Yolo County, is very familiar with FSA and its assistance programs, having served several years on the FSA County Committee for Yolo. “I’ve been fortunate not to have red blotch, but I know it’s a concern of many growers around California,” he said. “If you think you’re having a problem with red blotch, give your FSA office a call and see how they may be able to help you.”

FSA representatives said growers are not required to have federally subsidized crop insurance to be eligible for the program, however, they are required to complete and file USDA Form AD-1026 to verify conservation compliance requirements in order to receive TAP funds. There are 30 local FSA offices in California. Growers should contact their local office for information and application forms.

Red Blotch Research Update – Still No Vector Identified

Although grape growers and researchers have suspected an insect vector may be involved in spreading GRBaV in vineyards, both lab and field tests with numerous insects by different teams of researchers over the past three years have failed to provide evidence of an insect transmission of the virus in California. Researchers have conducted tests with different species of leafhoppers, mealybugs and sharpshooters, and more recently began testing whiteflies and treehoppers.

UC Berkeley entomologist Dr. Kent Daane has looked for possible GRBaV vectors since 2013, with funding from the American Vineyard Foundation. Daane’s research shows that some leafhoppers can sometimes acquire the virus by feeding on infected vines, but there is still no evidence to date that these leafhoppers can transmit the virus to another vine. In a presentation at UC Davis earlier this year, Daane said, “We’re trying to cover the gamut of common insects found in vineyards, and the insects that are not as common, and we’re looking at all mobile life stages of these species.”


“We’re trying to monitor possible red blotch movement based on newly infected vines in case we may stumble across a rare insect vector that may possibly move this around.” – Kent Daane, UC Berkeley


Adult variegated leafhopper, Erythroneura variabilis. Photo by Jack Kelly Clark, UC IPM.

Adult variegated leafhopper, Erythroneura variabilis.
Photo by Jack Kelly Clark, UC IPM.

Field surveys are being done in vineyards with infected vines. “We’re trying to monitor possible red blotch movement based on newly infected vines in case we may stumble across a rare insect vector that may possibly move this around,” Daane said.

He also explained: “The expression of symptoms of the pathogen in infected vines can vary from year to year. We’ve seen no pattern of movement or vine symptoms based on the use of insecticides, and we see no pattern of movement of red blotch in vineyards like we see with leafroll (that can be transmitted by mealybugs). In my opinion, there’s no evidence yet we should be treating for any of these vectors with insecticides solely because of red blotch.”

Entomologist Dr. Brian Bahder, a postdoctoral researcher working with Dr. Mysore Sudarshana of the USDA Agricultural Research Service at UC Davis, and UCD entomologist Dr. Frank Zalom, said their research to date has shown the same results as Daane’s. Speaking at the UCD Oakville Vineyard viticulture field day in Napa Valley on June 3, Bahder said, “We’re putting up sticky traps near infected vineyards, and testing caught insects for the GRBaV.” The traps have caught less common species of leafhoppers and mealybugs, along with treehoppers, whiteflies and aphids. The virus has been found in a small number of these insects. “We haven’t established a red blotch vector, but we’re now focusing on uncommon insects we find,” Bahder said.

UC Cooperative Extension Sonoma County viticulture advisor Rhonda Smith evaluated harvest yields and fruit quality parameters in 2013 and 2014 for vines testing positive for GRBaV in comparison with vines in the same vineyards that tested negative for GRBaV. This research was conducted in Napa and Sonoma Counties in four vineyards and includes data from 20 to 30 vines each of Cabernet Sauvignon, Merlot, Chardonnay and Zinfandel. Yield was reduced in 2014 in Chardonnay vines that were infected with GRBaV compared to uninfected vines. Yields were not significantly different in the other varieties.

A significant quality difference was in Brix levels, with reduced Brix at harvest for GRBaV infected vines of Cabernet Sauvignon (ranging from 4-20 percent), Merlot (6-16 percent) and Chardonnay (from 0-6 percent). The Zinfandel vines showed no significant differences. Smith said: “The accumulation of Brix was slower and less in red blotch positive vines. For Cabernet and Chardonnay, we experimented with dropping fruit before harvest to see if it would affect ripening, but it had no significant difference in improving ripening in the red blotch 2 positive vines.”