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Integrated Control of Potato Late Blight--Effects of Polygenic Resistance and Techniques of Timing Fungicide Applications. W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Phytopathology 67:415-420. Accepted for publication 14 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-415.

The efficiency of fungicide (as determined by degree of control per unit fungicide) used for control of potato late blight caused by Phytophthora infestans was enhanced when applied according to a “forecasting” technique. Fungicides usually were more effective if applied according to “Blitecast” than if applied after each 1.27 cm (0.5 in) of rain. The effect of polygenic resistance was maintained regardless of the method of fungicide timing. Therefore, the most efficient use of fungicide was to apply a reduced level of fungicide to a cultivar with polygenic resistance according to the “Blitecast” prediction. Analysis of apparent infection rates rather than final disease ratings reduced the error due to interexperiment interference.

Additional keywords: Solanum tuberosum, horizontal resistance.