Potato virus S (PVS) concentrations in plants grown from infected tubers were detected using enzyme-linked immunosorbent assay (ELISA) as early as two weeks after planting in the greenhouse, or three weeks after planting in the field. Maximum absorbance values from foliar samples were obtained eleven weeks after planting. Under laboratory conditions,Myzus persicae andAphis nasturtii transmitted PVS to 5.9%–14.3% of the plants tested, butMacrosiphum euphorbiae, Aulocarthum solani, andRhopalosiphum padi did not transmit. In similar trials, potato virus Y (PVY) was transmitted byM. persicae to 70 and 80%, respectively, of Red Pontiac and Jemseg test plants. Under field conditions, PVS was detected in 4% of leaf samples from Red Pontiac potato plants housed in screened cages with a virus source plant andM. persicae, compared to 0% of those from similar plants housed in screened cages with a virus source plant but without aphids. Subsequent testing of plants grown from the largest tubers produced under cages with and without aphids revealed infection rates of 73% and 0%, respectively, indicating that assays of current season leaf samples had substantially underestimated virus infection.