• Plant viruses can harm and even kill trees.Jupiterimages/Comstock/Getty Images
  
  Plant viruses can disfigure or kill a plant. They can be transferred through seeds, vegetative propagation, living organisms such as insects or bacteria and through mechanical means. When crops are infected with viruses, it can result in the loss of an entire season's worth of crops or plants.
  
  

Grapevine Fanleaf Virus

• Grapevine fanleaf virus is also known as Grapevine Gabler virus. It occurs throughout the world and is a grapvine pathogen that can be transmitted through plant sap, and is capable of spreading over medium and long distances. Symptoms of Grapevine Fanleaf virus include malformed leaves, discolored foliage (including yellowing), ringspots and a reduction in the size of grape bunches.
  
  

Citrus Psorosis Virus

• Citrus psorosis virus is found in mature citrus trees, typically aged at least 10 years. It is characterized by internal wood staining in the limbs and trunk, as well as bark scaling. There may also be reduced fruit yield and fewer leaves. This disease can occur in citrus-producing regions throughout the world.
  
  

Lettuce Mosaic Virus

• Lettuce mosaic virus can be seed-born in lettuce and also can be transmitted via sap and aphids. The disease is found worldwide. Symptoms typically including vein mosaic in older plants and vein clearing in younger plants. Non-host plants include tomato, cucumber, carrot, cabbage and sunflowers.
  
  

Tomato Bushy Stunt Virus

• A soil-borne virus, tomato bushy stunt virus can cause decreased production in tomato crops, as well as
  
  necrosis, line patterns, blotching and rings on the tomato fruit, which can make them difficult or impossible to sell. The yield loss in tomato plants afflicted with the virus can be as high as 80 percent. Other symptoms include leaf yellowing, stunted growth and fruit settling. Eggplants can also be afflicted by tomato bushy stunt virus.