EFFECTS OF SEASONAL FUNGICIDE SPRAYS ON PERITHECIUM FORMATION AND ASCOSPORE PRODUCTION IN VENTURIA INAEQUALIS

Seasonal sprays of the systemic fungicides benomyl, thiophanate-methyl, Bay Dam 18654 and Bavistin applied for the control of apple scab, Venturia inaequalis (Cke.) Wint., either completely or almost completely suppressed the production of ascospores in apple (Malus pumila Mill.) leaves overwintered in the orchard. In vitro production of perithecia on leaves sterilized with propylene oxide was also inhibited by these sprays, although some treatments suppressed ascospore discharge in overwintered leaves that failed to inhibit perithecium formation on the sterile leaves. Ascospore production was also reduced in leaves from spur clusters that had been sprayed with Dikar and metiram. In terminal shoot leaves from Dikar-sprayed trees, ascospore production was higher in leaves collected from near the tip than in leaves collected from near the base of the terminal growth.