Fungicidal control of Rhizoctonia solani in relation to soil texture, organic matter and clay minerals

In pot tests, MEMC, quintozene, captafol, carboxin, thiabendazole, carbendazim, benomyl and thiophanate-methyl used as seed treatments gave much better control of cowpea seedling rot in light-textured sandy and loamy sand soils than in heavy-textured loam and silt loam soils inoculated with Rhizoctonia solani. Disease control by chloroneb was not altered by soil texture. Amendment of sandy soil with montmorillonite reduced disease control with all fungicides, except chloroneb and carboxin; similar amendments with kaolinite decreased efficacy of MEMC and captafol. Green manuring with cluster bean reduced disease control by MEMC, captafol, benomyl and thiophanate-methyl; sunnhemp reduced efficacy of MEMC. Most fungicides gave poor disease control when farm yard manure or biogas sludge was added to soil, the sludge having the more marked effect. All the fungicides tested, except carboxin, were inactivated to different extents by humic acid extracted from farm yard manure.