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Ecology and Epidemiology

The Influence of Soil Temperature, Soil Moisture, Soil Texture, and Inoculum Density on the Incidence of Sorghum Downy Mildew. W. Schuh, Former graduate student, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843, Present address: Department of Plant Pathology, Oklahoma State University, Stillwater 74078-0285; M. J. Jeger, and R. A. Frederiksen. Associate professor, and professor, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843. Phytopathology 77:125-128. Accepted for publication 24 June 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-125.

The incidence of sorghum downy mildew was influenced by combinations of soil moisture-soil temperature, and soil texture-inoculum density. Statistical significance was determined using logistic regression. No significant interaction (P = 0.05) was observed within the parameters pairs. A soil temperature-soil moisture combination of 25 C and 0.2 bar and a soil texture-inoculum density combination of 80% sand content and 5 g of oospore powder per 100 g of soil gave the highest disease incidence. The results suggest that soils that are saturated after planting have soil temperatures below 20 C, or sand contents below 20% might be classified as disease suppressive.