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Influence of Selected Protectant Fungicides and Host Resistance on Simple and Complex Potato Late Blight Forecasts. V. J. Spadafora, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address: Department of Plant Pathology, Pennsylvania State University, University Park 16802; J. A. Bruhn(2), and W. E. Fry(3). (2)(3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853, (2)Present address: Chemicals Department, E. I. du Pont Co., Newark, DE 19711. Phytopathology 74:519-523. Accepted for publication 19 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-519.

Models of the initial deposition, weathering, and efficacy of triphenyltin hydroxide and captafol were developed and used in simulation studies designed to construct simple and complex potato late blight forecasts. The complex forecast recommended fungicide applications according to weather conditions, cultivar resistance, and fungicide type. In the simple forecast, sprays were recommended at fixed intervals according to cultivar resistance and fungicide type. In field experiments, spraying according to either method held final disease to levels of <5%. Fewer sprays were recommended for the moderately resistant cultivars than for the more susceptible cultivars.