Effects of fungicides on long-term cropping and fruit quality of apple

The effects on cropping of 24 applications, over a 3-year period, of each of five fungicidal programmes to control powdery mildew ( Podosphaera leucotricha ) were examined on the apple cultivar Cox's Orange Pippin. Trees receiving programmes based on ergosterol biosynthesis inhibitors (EBIs)-fenarimol, a triadimefon/bitertanol mixture and an experimental compound coded PP 347-each applied at 2-week intervals during the growing season had significantly ( c . 40%) less yield than those receiving the standard programme of binapacryl (not an EBI), applied weekly. Yield with a fourth EBI programme-based on penconazole-was also less than with binapacryl, but not significantly so. Both binapacryl and penconazole were used mixed with captan.
The lower yields were due to fewer apples harvested rather than to lower individual fruit weight. Possible reasons underlying these effects are discussed: the anti-gibberellin action of EBI compounds may be involved.