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Suppression of Rhizoctonia Damping-Off by Composted Hardwood Bark Medium. C. T. Stephens, Former Research Associate, Department of Plant Pathology, The Ohio State University, Columbus 43210.. L. J. Herr, H. A. J. Hoitink, and A. F. Schmitthenner, Professors, Department of Plant Pathology, The Ohio State University, Columbus 43210 and Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 65:796-797. Accepted for publication 2 March 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-796.

A postemergence inoculation method was used to evaluate the ability of a composted hardwood bark medium to suppress Rhizoctonia damping-off of seedlings in bedding plant flats. Celosia argentea 'Red Fox' seedlings were planted in two peat mixes and one composted bark mix and were inoculated at seedling emergence with one of two cultures of Rhizoctonia solani anastomosis group 4. After 6 days, significantly less damping-off had occurred in the composted bark mix than in the peat mixes. The highly virulent and moderately virulent isolates of R. solani caused 2.5 and 3 times more damping-off, respectively, in the peat mixes than in the composted bark mix in one test, and 4.0 and 9.5 times more damping-off in a subsequent test. The frequency of isolation of R. solani from symptomless seedlings taken from beyond the last damped-off seedling in a row decreased rapidly with increased distance in all soil mixes.