Once tolerated like a pesky younger brother, grape leafroll virus has grown up and become more than just a nuisance — but help is on the way.
After more than a year of correspondence and appeals, the Lodi Winegrape Commission has announced that the California State Farm Service Agency has approved leafroll virus as an eligible natural disaster that is covered under the Tree Assistance Program.
Leafroll is transmitted by the several species of mealybugs present in California orchards and vineyards, and, says Stephanie Bolton, Sustainable Winegrowing Director for the Commission: “Unfortunately it’s too late to eradicate the mealybug that has spread across the Lodi region and other parts of the state like wildfire.”
Compounding the problem, she says, “It only takes one vine mealybug 15 minutes to vector leafroll virus to a healthy grapevine and in Lodi, we have six or seven generations of mealybugs each growing season.”
She’s done the math and that means with every mating pair of mealybugs, the possible result is 22,781,250,000,000 more mealybugs, meaning a significant spread of viruses. In many cases, considerable damage is done before the virus is discovered, often one to two years after it has been introduced into a vineyard.
Leafroll virus inhibits photosynthesis that leads to decreased ripening of grape berries, lower yields, poor quality, and a decline in longevity of the vineyard. Mealybugs also vector another virus group of concern, vitiviruses.
“We’ve seen large patches of vines succumb to mystery or sudden vine collapse and we have evidence to believe that mealybugs are involved here too,” she says. “A combination of virus-sensitive rootstock, leafroll virus, and a vitivirus may result in the sudden death of acres of grapevines.”
TAP’s financial assistance
Enter the USDA’s Farm Service Agency Tree Assistance Program or TAP for short. Using funds from the Farm Bill, TAP provides financial assistance to eligible growers experiencing a natural disaster, like relief from grapevine red blotch virus approved in 2015.
“It’s been difficult to convince the average farmer to spend money on leafroll management strategies — like vine mealybug biocontrol, ant control, virus testing, or the removal of virus-infected vines and we continue to learn the most economically-efficient and accurate means of implementing these mitigation strategies,” Bolton says.
“Removing virus-infected grapevines is the number one most efficient thing a grower can do to reduce the impact and spread of leafroll virus and the recent approval of TAP funding will be a real game-changer in the fight to reduce the virus impact and protect the winegrape industry.
“TAP financial assistance may represent the support needed for concerned growers to remove the virus inoculum harbored in their vineyards and replant with California Department of Food and Agriculture-certified material.”
According to San Joaquin County FSA program technician Joanne Gomez, growers may apply for up to a thousand acres a year and recoup 65% of certain removal and replanting costs.
Gomez points to the TAP Fact Sheet qualifications: “Growers must own the vines that have suffered a qualifying loss in excess of 15% mortality for the stand and replace them within 12 months from the date the TAP recommendation is approved.”
A loss claim from leafroll (or red blotch virus) must be verified through testing performed at a commercial laboratory (with a minimum of 10 symptomatic vines tested from each claimed infected block).
For more news on pests, disease management and other issues affecting vineyards, subscribe to the bi-monthly newsletter The Grape Line.
Source: Lee Allen, Western Farm Press
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