Over 80 graft-transmissible agents (viruses, virus-like agents and phytoplasmas) are known to occur in grapes. Three of the more important viruses in the United States, listed here, can greatly reduce yield and negatively affect fruit and wine quality, by reducing sugar content, affecting fruit color and increasing fruit juice acidity. The extent of the effects is dependent on many factors, including cultivar, rootstock, environment, and cultural practices.
|Grapevine leafroll associated viruses (GLRaVs) are members of the family Closteroviridae; most of them are vectored by mealybugs and soft scales.|
|Grapevine fanleaf virus (GFLV) is a member of the family Secoviridae and is vectored by the dagger nematode Xiphinema index.|
|Grapevine red blotch virus (GRBV) is a member of the family Geminiviridae and transmitted by the three-cornered alfalfa hopper, Spissistilus festinus (Hemiptera: Membracidae) in experimental conditions.|