Grapevine Leafroll Viruses
Grapevine Leafroll-Associated Viruses (GLRaVs)
The host range of the GLRaVs includes V. vinifera, American Vitis spp. and hybrids.
Leafroll is probably the most widespread virus disease of grapevines. Leafroll symptoms are associated with at least nine different viruses that are referred to as Grapevine Leafroll-Associated Viruses (GLRaVs). The distinct viruses are referred to as GLRaV-1 through GLRaV-9. Laboratory ELISA tests are only commercially available for six GLRaVs. GLRaV-1 and GLRaV-3 are the most commonly found viruses in the group.
Grapevines infected with leafroll often show downward curling of the leaves and leaf thickening. The leaves of red fruited varieties may turn red in late summer while the veins may remain green. White fruited varieties may not show reddish color and only show downward leafroll. Infected plants are more susceptible to environmental stress. The fruit may have poor color development, a 25 to 50 percent- reduction in sugar content, and delayed maturity. Yield is reduced due to inhibition of cluster formation and development.
The virus is spread primarily by movement of infected propagation material. Some insects (mealybugs and soft scales) have been shown to transmit the disease under experimental conditions, but it is not known if this method of transmission is important in Oklahoma. Transmission by mealybugs is very slow under field conditions.
Growers should plant certified, disease-free plants. Pruning tools should be disinfected with a bleach solution (1 part household bleach, 9 parts water) between cuts. Infected plants should be removed and discarded.