Control of Grapevine Leafroll Disease Spread at a Commercial Wine Estate in South Africa: A Case Study

Abstract

Grapevine leafroll disease (LR) is a serious disease of grapevine worldwide. Grapevine leafroll-associated virus 3 (GLRaV-3) is the most prevalent virus associated with this disease in South Africa and, despite a successful virus-elimination strategy within a certification scheme, spreads rapidly in local commercial vineyards. Since 2002 an integrated control strategy was used at a commercial wine estate to control LR and serve as a case study for the local and international wine industries to show that control in a commercial setting is possible. The strategy included planting of certified material tested free of detectable viruses, use of herbicide and subsequent removal of infected vine material, fallow periods during which time volunteer hosts were removed, and use of systemic and contact insecticides, sanitation, and horticultural practices to minimize spread of viruliferous mealybugs. Leafroll was reduced from a 100% infection in 2002 on 41.26 ha (111,431 vines) planted mainly from 1989 to 1992, to only 58 LR infected vines detected in 2012 on 77.84 ha (209,626 vines), an incidence of 0.027%. This reduction was achieved by replacing the fully infected vineyards and roguing 3105 infected vines within young and replaced new vineyards. The control strategies were successful in curtailing the spread of LR disease and have resulted in the removal of the disease from the majority of individual vineyards. Leafroll currently occurs at sufficiently low levels in the remaining vineyards that local eradication may be possible in these, in contrast to the general situation in the South African industry where the majority of producers do not apply LR control strategies and leafroll is widespread.