Evaluation of Benomyl and Propiconazole for Controlling Sheath Blight of Rice Caused by Rhizoctonia solani

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Abstract
Twenty-one isolates of Rhizoctonia solani were sensitive to benomyl (mean EC50 0.5 .mu.g a.i./ml) and propiconazole (mean EC50 5.2 .times. 10-2 .mu.g a.i./ml) in vitro. Radial growth rates for all isolates on unamended PDA averaged 0.96 mm/hr. In field trials, propiconazole applied twice or propiconazole followed by benomyl significantly reduced disease severity and increased yields in three of six studied during 1984-1985 on the semidwarf rice cultivar Lemont. Yield response was related to incidence of sheath blight at the panicle differentiation growth stage. Benomyl applied twice did not significantly reduce disease or increase yields. An economic return from propiconazole/propiconzole or propiconazole/benomyl could be anticipated when more than 5% diseased tillers were observed at the panicle differentiation growth stage.