Green peach aphid,Myzus persicae(Selzer), populations were monitored and examined for pathogens at Moscow and Troy, ID, in 1991 and near Yakima, WA, in 1991–1992.M. persicaeinfesting a peach orchard, broadleaf weeds within and around the periphery of the orchard, and nearby potato fields near Yakima were observed from March until November. Potatoes and nonsolanaceous plants in home gardens in Moscow and Troy also were monitored forM. persicaeand examined for pathogens during the growing season. In 1991, aphid numbers reached a maximum of 6,070 per 5–15-cm peach twig segments on 29 May but only nine per 15–0.15-m twig segments in 1992. Fungal pathogen activity was barely discemable on tree-borne aphids in the orchard but was observed more frequently from aphids infesting weeds beneath the trees. An epizootic of Entomophthorales occurred on aphids infesting solanaceous (potatoes) and nonsolanaceous hosts in home gardens in Moscow and Troy, (Latah County), Idaho, in 1991.Verticillium lecanii(Zimmerman) Viegas was identified fromM. persicaeon peach leaves;Beauveria bassiana(Bals.) Vuillemin andConidiobolussp. were identified from aphids on potatoes. Aphids collected from weeds growing in and near the peach orchard were infected withEntomophthora chromaphidisCornu,Conidiobolus coronatus(Constantin) Batko,C. obscurus(Petch) Hall&Dunn, andV. lecanii.Aphids on potatoes and nonsolanaceous hosts at Moscow and Troy were infected withPandora neoaphidis(Remaudiere&Hennebert) Humber,E. chromaphidis, andConidiobolusspp. Aphid populations were much lower in 1992 both within the orchard and in potatoes.