| Summary: | A quantitative technique has been developed to assay cotton soils for populations of Thielaviopsis basicola, a soil occurring fungus that causes the seedling disease of cotton known as Black Root Rot. The procedure utilizes a soil dilution technique with a carrot extract agar containing etridiazol, Mystatin, streptomycin sulfate, chlortetracycline, calcium carbonate and PCNB. Populations of the fungus have been monitored from April to December, 1986 in a heavily infested Pima S-6 field in cooperation with Bob Cockrill, a Coolidge grower. When field soils containing approximately 600 propagules of the fungus per gram of air dry soil were planted to Pima S-6 in the laboratory, 75-100% and 50-75% cortical decay occurred at 20 and 28 C, respectively. This seedling damage was related to subsequent reduced seedling vigor.
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