Incidence of diseases on fruit of nine apple genotypes as influenced by six fungicide treatments

Nine apple genotypes (three commercially important cultivars, three disease-resistant cultivars, and three disease-resistant selections) were sprayed with fungicides during the early- and/or late-season for two fruiting seasons to evaluate the occurrence of disease symptoms on the fruit. Apple scab, cedar-apple rust, quince rust, and powdery mildew symptoms were rare on all genotypes regardless of fungicide treatment. In general, fungicide applications from second cover spray through late Aug. controlled summer diseases more effectively than early-season treatments. Although there was some year-to-year variation, rot incidence was consistently lowest for NY 74828-12 and highest for 'York,' 'Golden Delicious,' and 'Liberty.' Flyspeck incidence was lowest on 'Redfree,' moderate on 'Freedom' and NY 74828-12, and greatest on 'Liberty' and NY 73334-35. 'Redfree' and NY 74828-12 consistently had the least sooty blotch. These results indicate that apple genotypes vary in their susceptibility to summer diseases, and that it may be possible to breed genotypes with improved summer disease resistance.