Some factors affecting the control of Rhizoctonia solani by systemic and non‐systemic fungicides

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Abstract
SUMMARY: In laboratory tests, Rhizoctonia solani grew best on agar at 30 oC and pH 5‐5. Mycelial growth was strongly inhibited by benomyl, chloroneb and quintozene, less so by thiophanate‐methyl. The optimum temperature for inhibition was 25 oC for quintozene; the other three fungicides gave greatest inhibition at the lowest temperature tested (20 oC). Benomyl and thiophanate‐methyl were most inhibitory at pH 7–8, chloroneb and quintozene at pH 5–6.In pot trials using mung bean, long melon, egg‐plant, common pea and sugar beet, R. solani caused maximum disease at 20 oC and in wet and alkaline soils. As seed treatments, benomyl and thiophanate‐methyl gave optimum control at 20 oC and pH 7‐6; chloroneb and quintozene were most effective at 30 oC and pH 5‐4. All four fungicides gave maximum control on plants growing in wet sandy loam.Comparisons of host effects showed that, on all the four hosts tested, thiophanate‐methyl wettable powder at 0.25% (0.175% a.i.) gave 90% control, chloroneb w.p. at 0.3% (0.195% a‐i‐) gave 80% control on mung bean and sugar beet, benomyl w.p. at 0.3% (0.15% a.i.) was satisfactory on mung bean, egg‐plant and sugar beet but not on long melon, quintozene w.p. at 0.3 % (0.225 % a‐i‐) gave effective control on sugar beet only.The senior author is grateful to the Council of Scientific and Industrial Research, New Delhi, India, for the award of a Research Fellowship for undertaking these studies. Thanks are due to Dr S. D. Gupta and Mr S. L. Verma for determining the soil characteristics.