Effects of fungicides on apple crown rot caused by Phytophthora cactorum

The mycelial growth of Phytophthora cactorum on corn meal agar was completely inhibited by metalaxyl or mancozeb at 50 or 100 μg ml−1, but not by fosetyl‐aluminium at the same concentrations. Soil drenches with metalaxyl, followed by metalaxyl+mancozeb, around the base of naturally infected trees under orchard conditions, prevented the growth of P. cactorum in the infected bark of the tree. Soil drenchs with metalaxyl, followed by metalaxyl+mancozeb, also prevented the infection of apple trees with P. cactorum under orchard conditions. The trunk circumference and spur length were not significantly affected by any of the fungicide treatments in all the trials over 2 years, except in one of the four orchards used in the study. Soil drench with metalaxyl alone, or followed by metalaxyl+mancozeb, may provide an effective control method for crown rot of apple trees.