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Effect of Soil Temperature and Soil Amendments on Thielaviopsis Root Rot of Sesame. Peter B. Adams, Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; Phytopathology 61:93-97. Accepted for publication 21 August 1970. DOI: 10.1094/Phyto-61-93.

Soil amended with alfalfa hay, corn stover, and cabbage tissue substantially reduced red root of sesame caused by Thielaviopsis basicola in greenhouse experiments. In the field, alfalfa hay and corn stover provided no significant control. In a crop rotation study, no significant control was obtained when sesame followed oat, corn, or cabbage. In the greenhouse at a temp at 15 C, alfalfa hay provided no control, whereas at 20 and 25 C, alfalfa hay provided substantial control. At 30 and 35 C, red root was controlled by temperature alone. When the soil temperature was cycled 10 hours at 25 C and 14 hours at 30 C, disease severity was significantly less than that at constant 25 C, and similar to that at constant 30 C. Maximum germination of chlamydospores of T. basicola in soil was obtained at 25 C, with percentage of germination declining rapidly to zero at 35 C. Use of clear plastic mulch in the field to raise the soil temperature provided significant control of red root 7 weeks after planting, but not 12 weeks after planting.