Grapevine leafroll is probably the most widespread virus disease of grapevines worldwide. There are currently nine different viruses associated with leafroll, but grapevine leafroll-associated viruses 1 and 3 are most commonly found.
In the national grapevine survey conducted in 1994-1995, GLRaV-1 was present in 1.0% of samples tested, whereas GLRaV-3 was present in 10.5% of samples tested nationally. Since then, grapevine leafroll-associated viruses 2, 4 and 5 have been detected in imported grapevines.
Leafroll virus has impacts on both vine health and grape quality. Growth and yield may be reduced by 10-70%.
Typical leaf symptoms include reddening of the leaves between major veins in red varieties and yellowing of the leaves between major veins in white varieties. Leaves become thick, brittle and roll downwards.
The virus reduces yield by inhibiting cluster formation and development. Infected vines have an increased sensitivity to environmental stress. Impacts on quality include delayed maturity of grapes, a 25-50% reduction in sugar content and poorly coloured fruit.
Long distance spread occurs primarily by movement of propagation material from infected plants.
Several mealybug and soft scale insect species have been shown to transmit leafroll associated viruses under experimental conditions.
Rapid leafroll spread has been reported in European vineyards having significant insect vector populations. In California, increasing natural spread within vineyards has been observed. The common grape mealybug (Pseudococcus maritimus), which occurs in the Okanagan, is a vector of GLRaV-3.
