Virus Diseases of American Pasture and Forage Crops

The incidence of virus diseases in forage and pasture crops, primarily grasses and legumes, although studied relatively little compared to other crops, has been shown to be high, especially in the legumes. This chapter attempts to summarize what is known of the viruses and virus diseases of pasture and forage crops in the USA. The crops have been divided into legumes and grasses, and the virus diseases of each are discussed relative to geographic regions of the country. Attention to the legume crops, with emphasis on alfalfa and true clovers, reflects the relative research effort in the USA on this plant family. Permanent pastures cover about 33.4 million ha of crop land in the eastern USA, where an additional 8.1 million ha is planted to annual pastures. The highest incidence of the virus in the western region of the USA occurs in the Pacific Northwest.