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Rhizoctonia Disease of Potato: Effect on Yield and Control by Seed Tuber Treatment. A. R. Weinhold, Professor, Department of Plant Pathology, University of California, Berkeley 94720. T. Bowman, Staff Research Associate, Department of Plant Pathology, University of California, Berkeley 94720; and D. H. Hall, Extension Specialist, University of California, Davis 95616. Plant Dis. 66:815-818. Accepted for publication 3 December 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-815.

Based on an individual plant sampling procedure, Rhizoctonia stem and stolon canker influenced the production of both marketable and cull tubers of Solanum tuberosum. As disease severity increased, there was a decrease in the percentage, by weight, of marketable tubers and a corresponding increase in the percentage of cull tubers. The disease was effectively controlled in commercial fields in Kern County, CA, by dipping seed tubers in a 2% solution of formaldehyde. The increase in percentage of marketable tubers that resulted from controlling stem and stolon canker by seed tuber treatment was consistent with predictions based on individual plant sampling data. The seed tuber treatment also resulted in a marked improvement in the appearance of progeny tubers. Disease control by seed tuber treatment and soil assay data provided evidence that the pathogen was not present in these soils and that lesions on plants from nontreated tubers developed from tuberborne inoculum. The pathogen was present in the soil in the Tulelake area, and seed tuber treatment did not control Rhizoctonia stem and stolon canker.