Patterns in the numbers of air-borne conidia of apple powdery mildew, Podosphaera leucotricha (Ell. and Ev.) Salm., and their relevance to control measures

摘要

Abstract Air-borne conidia of apple powdery mildew, trapped for two seasons, showed a marked seasonal periodicity. Spore concentration rose rapidly in spring (October) to reach a peak in early summer (November) then declined until the end of February. No evidence was found for a weekly periodicity of spore release. Fungicidal spray experiments in a third season demonstrated the importance of close-interval spray application during spring (October—November), the period during which apple trees show active extension growth. Such spraying was important both in reducing current season build-up of infection and in preventing the formation of overwintering sources of primary infection in buds.