Grapevine leafroll disease, caused by a complex known as grapevine leafroll-associated viruses, is a worldwide threat to vineyard health and sustainability. Mealybugs are the main agents (vectors) responsible for virus movement between vines in the field. This project continues to study the relationship between mealybug populations and the incidence of leafroll disease in vineyards. The ultimate goal is to develop and deploy best management practices for leafroll disease and vineyard mealybugs as vectors of leafroll viruses. The project not only focuses on development of these practices, but also works with grape growers to use these tools in a disease management program. For example, we have successfully developed the use of male GMB traps as a monitoring and decision-making tool and provided significant formal and informal educational efforts on the use of these traps. Traps are more sensitive detection tools that can supplement labor-intensive ground surveys. We provided training sessions on trap deployment and male mealybug identification to ensure that the traps are being used correctly, at the appropriate time of year, and that the trap data are useful to growers. Grape growers are increasingly adopting the use of GMB traps as a management tool. We have also worked with growers to explore and implement other effective and timely management practices, such as insecticide sprays and vine removal.
Our preliminary analysis has shown that prior infection rates of leafroll disease and mealybug populations in the current year will affect the number of vines that develop leafroll disease symptoms in the following year. This has implications for vine removal programs: in a given year, there may be a percentage of vines that contain virus particles but are not showing disease symptoms. This and other complementary projects worldwide are developing best management practices for leafroll disease management that include monitoring and management of vector populations, identification and removal of diseased vines or vineyards, planting of material free of known grapevine pathogens, and regional approaches to management. In future studies we propose to continue to develop new practices, fine-tune current practices to determine when, where and how they can be used most effectively, develop a regional approach to management, and strengthen our educational efforts.