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Biological Control of Rhizoctonia Stem Canker and Black Scurf of Potato. J. E. Beagle-Ristaino, Department of Botany, University of Maryland, College Park 20742, Present address of senior author: Department of Plant Pathology, University of California, Davis 95616; G. C. Papavizas, Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, ARS, Beltsville, MD 20705. Phytopathology 75:560-564. Accepted for publication 3 December 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-560.

The efficacy of several fungal antagonists for control of Rhizoctonia solani on potato was evaluated in greenhouse and field tests. Fermentor biomass (FB) preparations of Trichoderma viride (T-1-R9) and Gliocladium virens (G1-21) applied as dusts to seed potatoes infested with sclerotia of R. solani before planting, reduced disease incidence in the field by 50 and 55%, respectively. Viability of sclerotia from seed pieces retrieved from the field was reduced 54- 89% by specific antagonists. In the greenhouse, up to 88% reduction in germination of sclerotia was obtained by treating sclerotia-infested tubers with FB of T-1-R9 before planting. FB preparations of T. viride (T-1-R9), T. harzianum (WT-6), T. hamatum (Tri-4), and G. virens (G1-21) added to the soil in a mixture of pulverized pyrophyllite (anhydrous aluminum silicate), significantly reduced numbers of propagules of R. solani. After 4 wk, populations of R. solani were eliminated in soils infested with FB of Tri-4. Population levels of the antagonists increased 1,000-fold within 4 wk. Sclerotia of R. solani retrieved from antagonist-amended soils were heavily colonized by the antagonists. The viability of colonized sclerotia was reduced 13- 100%. Results suggest that both soilborne and tuberborne propagules of R. solani can be effectively reduced by biological means.