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DMI Fungicides on Apples: Survival of the Apple Scab Pathogen in Sprayed Leaves, Late-Season Scab, and Sustainability of DMI Use in IPM Programs 1997

Project Leaders: David M. Gadoury, Robert C. Seem, and Wayne F. Wilcox


1. Determine the impact of use patterns of a DMI fungicide upon survival of infections and delayed symptom expression.

2. Determine the potential impact of such survivorship upon selection for resistance to DMI fungicides.


The DMI fungicide fenarimol significantly reduced the establishment of the apple scab pathogen on sprayed trees. However, despite the shortening of the interval between applications from 14 to 7 days, lesions formed abundantly on trees first sprayed 96 hours after inoculation. As in 1996, the first wave of lesions that appeared represented only a portion of the total, and lesions continued to develop for several weeks from a single infection period. Whether or not this is due to resistance to fenarimol will be known once sensitivity assays are completed in 1998.