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Quantification of General Resistance of Potato Cultivars and Fungicide Effects for Integrated Control of Potato Late Blight. W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Phytopathology 68:1650-1655. Accepted for publication 8 May 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1650.

Areas under the disease progress curves were more reliable than the apparent infection rates or final disease ratings for the quantification of effects of fungicide and general resistance on infection by Phytophthora infestans in potatoes. General resistance and fungicide application each reduced disease increase and the effects of each were additive. This relationship between general resistance and fungicide was similar whether fungicide dosage was adjusted by altering the concentration of weekly applications or by varying the intervals between applications. Among eleven commercial cultivars and one breeding line, the difference in general resistance between the most resistant and most susceptible clones was estimated to be equivalent to weekly applications of about 0.7 kg mancozeb (a.i.)/ha. Growers should be able to complement general resistance in potato cultivars by adjusting fungicide either by altering the dose per scheduled application or by altering the interval between applications.

Additional keywords: disease management, epidemiology.