Influence of potato cultivars on the effectiveness of fungicide control of early blight

Three potato cultivars differing in degree of susceptibility to early blight were grown under crop management practices typical for Pennsylvania in 1987 and 1988. There were three experimental treatments: no fungicides, mancozeb with weekly applications initiated at 7 or 8 weeks after planting (early treatment), and weekly applications initiated at first symptoms of disease (late treatment). The no-fungicide control treatment had significantly higher AUDPC values than either treatment with fungicides and the no-fungicide treatment had significantly lower yield in 1987 but not in 1988. Tubers from the no-fungicide control had lower specific gravity. Norchip, the cultivar most susceptible to early blight examined in this study, responded the most in yield increases by the increased fungicide applications.