Grapevine Leafroll-Associated Virus (GRLaV)

While leafroll affects a grapevine's quality and yield at harvest, the long term effect of GLRaVs can destroy vineyards and is a serious issue in viticulture. Leafroll affects red and white wine grape varieties, but it can be difficult to detect until the virus is established in the vines and in the vineyard. By the time the virus is detected, the vines may not be able to produce the quality of grapes needed for wine production. Visual cues are easier to detect in red wine grapes in both the spring and fall, with the fruit of red wine grapes remaining green longer and having a faded or less vibrant color at harvest, along with fewer berries overall. When the virus has become fully established in the vine, the vine suffers and appears to have less vigor, and the leaves of the vine will curl, which is how the common name of leafroll came to be used to describe GLRaVs.

GLRaVs are complex, spread rapidly often before vineyard managers even know the vines are infected, and are almost impossible to detect; different vine species react differently to the GLRaVs. While some strains will cause symptoms, not all do. By the time the virus is detected, the vine may be seriously damaged and the vineyard will have to take corrective measures get the virus out of the vineyard and replant the vines. The mealybug-spread GRLaV-3 is a particularly nasty strain of the virus which infected vines in New Zealand and reduced crop yields by 60%.

Once the virus is established in the phloem tissue, it disrupts normal function and the vine will not be able to distribute nutrients properly, which results in the tissues of the vine becoming stunted; leafrool interferes with the development of sugar and metabolic composition of the fruit.