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Southern Corn Leaf Blight Development Relative to Temperature, Moisture, and Fungicide Applications. N. C. Schenck, Plant Pathologist, University of Florida, Gainesville 32611; T. J. Stelter, Field Development, Rohm and Haas Co., Philadelphia, Pennsylvania 19105. Phytopathology 64:619-624. Accepted for publication 1 November 1973. DOI: 10.1094/Phyto-64-619.

Southern corn leaf blight (SCLB) became severe on field corn at Gainesville and Lakeland, Florida, when minimum temp were 20 C or above and relative humidity (RH) was 100% for 6 h or more on several consecutive nights. These parameters for severe SCLB development in the field agree with results of others and indicate warm, moist weather favors SCLB epidemics. SCLB severity and rate of development were greater on Texas male-sterile than on normal cytoplasm hybrids, indicating that race T of the pathogen was predominant. SCLB became moderately severe on nonsprayed plants 12-14 days earlier than on plants sprayed weekly beginning at or before tasseling. Mancozeb at 1.7 kg/ha effectively controlled SCLB when applied by airplane in 28.0 or 23.4 liters of water/ha or when applied with ground equipment in 935 liters of water/ha. Yields from plants with effective disease control were consistently better than nonsprayed plants, but yields were not statistically correlated with disease incidence.

Additional keywords: Helminthosporium maydis, Zea mays.