Bioactivities of five fungicides against Rhizoctonia solani, the causal agent of tobacco sore shin

Tobacco sore shin caused by Rhizoctonia solani is one of the most destructive diseases in the seedbed suffered by tobacco in China. This study evaluated the activities of the fungicides azoxystrobin, boscalid, fluazinam, propiconazole, and pyrimethanil against mycelial growth, sclerotia formation and germination of R. solani, and also their protective and curative efficacies against tobacco sore shin. The mycelial growth of R. solani was more sensitive to fluazinam and azoxystrobin than to propiconazole and boscalid, and least sensitive to pyrimethanil. Azoxystrobin showed stronger inhibition of sclerotia production than propiconazole, fluazinam, pyrimethanil, and boscalid. None of the five fungicides inhibited the sclerotia germination of R. solani. In terms of the protective activity of detached tobacco leaves, azoxystrobin and boscalid at 12.5 and 50 mg/L were superior to fluazinam, propiconazole, and pyrimethanil in reducing sore shin. For curative activity, azoxystrobin at 50 and 200 mg/L was superior to the other four fungicides in reducing disease. Therefore, among the five fungicides, azoxystrobin is most suitable for the control of tobacco sore shin.