Impact
Two potato mosaic viruses that are important in the San Luis Valley are Potato Virus X (PVX) and Potato Virus Y (PVY). PVX is known as potato latent virus disease, potato mottle or latent mosaic. PVY causes severe or rugose mosaic. PVY is reported to cause losses ranging from 10 to 80 percent, depending on the potato cultivar. The primary effect of both viruses is a reduction in yield and size of daughter tubers. The Colorado seed certification program minimizes the impact of these viruses in the San Luis Valley by conducting an extensive testing program.

Descriptions and Symptoms
PVX
	PVX usually causes few or no symptoms in most cultivars and can be carried in seed stocks unnoticed.
	PVX is readily transmitted mechanically. It is spread by foliar or sprout contact, seed cutters, pick-type planters, cultivators, spray equipment, and possibly by insects with chewing mouthparts.
	Some strains alone, or in combination with PVY, may cause rugose mosaic.
PVY
	PVY is a stylet-borne virus transmitted by at least 30 species of aphids, particularly the green peach aphid and potato aphids. Cereal aphids in high numbers become important vectors of PVY.
	Symptoms of PVY may vary by cultivar. Necrosis and veinal necroses of petioles often cause leaves to drop or cling to the stems. Infected plants have bunchy tops and leafless lower stems or clinging necrotic leaves. In Russet Norkotah, visible symptoms do not become well developed.
	Aphids landing on infected plants acquire PVY within a few seconds of fedding and can transmit the virus immediately, in a non-persistent manner. While aphid transmission is the most important means of spread in the field, all PVY strains also are mechanically transmissible by leaf contact and may be carried in seed tubers.
	Current-season infection late in the growing season may not cause foliar symptoms.
Integrated Management
	Plant high quality, pathogen tested, certified seed.
	Conduct a strict sanitation program including use of detergents.
	Destroy volunteer potatoes which may harbor PVX or PVY.
	Avoid cutting seed that is extensively sprouted.
	Complete cultivation, hilling and other post emergence operations when plants are less than 6 to 8 inches tall.
	Control of aphids is an important component of a management program for viruses. However, this action will not control PVY. Kill vines early to avoid late season aphids flights.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.