Documentation of grapevine leafroll-associated viruses in wine grape varieties and native grape species in Virginia, and examination of the movement of grapevine leafroll disease to develop management strategies

Grapevine leafroll-associated virus-2 (GLRaV-2), GLRaV-3, and grapevine fleck virus (GFkV) are widespread in grapes around the world. These viruses can cause significant crop loss and affect wine quality by reducing sugar accumulation and compromising skin color. Mealybugs are vectors of grapevine leafroll-associated viruses (GLRaVs). A statewide survey of commercial and wild grapevines in Virginia was conducted during 2009 through 2011. Also, vector management options were tested in two field studies. GLRaV-2, GLRaV-3, and GFkV were detected in 8%, 25%, and 1%, respectively, of over 1,200 vine samples (41 wine grape varieties) from 77 locations, and 64% of vineyards were positive for at least one of the tested viruses. All 100 wild grapevines tested were free of these three viruses, indicating that they are not alternative hosts. The majority of infected vines from commercial vineyards were planted prior to the 1990's; however, some new plantings were also found to be positive, indicating movement of the viruses among vineyards and also potential infection prior to planting. The high frequency of virus-infected vines emphasizes the importance of clean plant materials, as well as management of vector insects. The insecticide trials resulted in promising vector control with dinotefuran and spirotetramat; however, acetamiprid and pryrethroid resulted in an increase in mealybug population. This study is the first to examine multiple grape viruses in VA. It will aid in developing better strategies aimed at controlling mealybugs to restrict the movement of viral diseases.