COMPARATIVE EFFECTIVENESS OF SOME ORGANIC AMENDMENTS AND FUNGICIDES IN REDUCING ACTIVITY AND SURVIVAL OF RHIZOCTONIA SOLANI IN SOIL

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Abstract
Cellulose powder, oat straw, and soybean hay enriched with NH4NO3 to produce C/N ratios of 60, 30, and 10, respectively, were just as effective as the fungicide PCNB and more effective than the fungicides H 3944 and CP 30249 in reducing the saprophytic activity of Rhizoctonia solani in artificially infested non-sterilized soils 4 weeks after incorporation. One week after incorporation only oat straw and the three fungicides at 50 and 100 p.p.mf. of the active ingredient reduced R. solani activity appreciably. The effectiveness of CP 30249 and PCNB in reducing the saprophytic activity of 5 R. solani clones in soil depended on the fungicide and inoculum concentrations and on the different sensitivities of the clones. Oat straw with C/N ratios of 30 and 80 was more effective in reducing the survival of R. solani in precolonized substrate segments than oat straw with C/N ratio 10 and PCNB at 25 and 50 p.p.m. High decolonizing ability of oat straw with low N content was associated with increased numbers of actinomycetes and bacteria in soil. The sensitivity of R. solani to amendment decomposition and fungicidal action was greater before the fungus saprophytically colonized the substrate than after it became established within the substrate.

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