Grapevine Leafroll Disease (GLRD) is a devastating viral infection that can affect grapevines in all regions.
Recently, researchers at Cornell University, including Miguel Gómez and Katie Ricketts, conducted an economic analysis in the Napa, Sonoma, and northern San Joaquin Valley grape-growing regions to determine the economic losses caused by leafroll disease, as well as the best control strategies to minimize losses.
Survey data was collected from vineyard managers throughout California’s grape-growing regions with a focus on GLRD’s impact, specifically on Cabernet Sauvignon. The researchers looked at cost-minimizing management strategies under various disease levels, as well as price penalties, timing of disease onset relative to vineyard age, yield losses and control costs.
Controlling The Disease
“We found that vineyard managers adopt varied strategies for managing GLRD,” Gómez says.
Some of those strategies include roguing individual symptomatic vines and replacing them with certified vines derived from clean, virus-tested stocks, applying insecticides targeting mealybug vector populations, and fully replanting vineyards when disease symptoms develop. Some growers, however, choose not to control GLRD at all.
“However, we know very little about cost-minimizing control strategies,” Gómez says. “Our research addresses this industry need.”
According to Gómez and Ricketts, GLRD might not be a cause for immediate vine removal for some growers, because infected vines can still produce some fruit.
“Some growers believe that a producing vine — even when diseased — can be preferable to pulling the plant,” Gómez says.
For grapes intended for high-value markets, keeping an infected block could reduce quality, depending on the severity of the disease.
“But perhaps more importantly, GLRD infection may reduce a grower’s power to negotiate future contracts or for contract renewal, which can mean a large and immediate economic impact,” Gómez notes.
Over the lifetime of a typical vineyard, losses from GLRD can range from $29,902 to $226, 405 per hectare, the research found. Growers will want to take different courses of action depending on the severity of the disease. For example, Gómez and his colleagues found that roguing symptomatic vines and replanting them with certified ones, combined with applying insecticides to reduce mealybugs, can minimize losses if GLRD prevalence is low (between 5% and 10%). However, when disease prevalence is at 25% or higher, in most cases, a full vineyard replacement is the best option.
“Our findings underscore the importance of investing in GLRD management strategies, including the purchase of certified planting material as an upfront investment for reducing the spread and impact of GLRD,” Gómez says. “Growers should consider the extra cost of buying tested material as an insurance for protection against future losses due to GRLD, and growers should support efforts to implement statewide and region-wide clean plant certification systems to avoid spreading the disease across vineyards.”