We compared importance of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphormae (Thomas), apterae and alatae in secondary spread of potato leafroll virus (PLRV) and the control achieved with foliar sprays alone to that of conventional practice using a soil systemic. Density gradients of apterae were produced by application of insecticidal sprays. Spread of PLRV from centrally located infector units was monitored in foliage serologically. PLRV infection ranged from 23.7 to 74% in 1985 and 12.3 to 77.2% in 1986. PLRV infection was significantly correlated with cumulative green peach aphid and with potato aphid apterae-days both years. Green peach aphid was more abundant than potato aphid and alatae were few both years. At all distances (1-5 m) from infector units, infection across rows was 38.7-60.6% of that within rows. Steep gradients of PLRV infection with distance from infector units indicated short-distance movement of vectors and suggested that apterae were of prime importance in PLRV spread. Check plots without a PLRV source and not augmented with green peach apllid (1986 only) had a final PLRV incidence of 1.5%, indicating only minor invasion of these plots by viruliferous alatae. Weekly application of methamidophos sprays reduced PLRV incidence to that in plotstreated with aldicarb at planting and weekly methamidophos sprays. It should be feasible to develop a seed potato pest management program for Minnesota based on foliar sprays alone.