AbstractThe host range of theEntomosporiumfungus was proved to be limited to the Rosaceae, especially to the sub‐familyPomoideae, through comprehensive inoculation experiments. No pathogenic strains occurred among the isolates from different hosts. The fungus overwinters on diseased leaves on trees or on the ground and on lesions on young twigs. Conidia on them serve as the source of primary infection in spring. Formation of the perfect state was not observed in Japa