Oryza sativa; Deperissement; Rhizoctonia; Controle de maladies; Fongicide; Sri lanka
ShB [sheath blight] caused by Rhizoctonia solani Kuhn (Thanatephorus cucumeris) is a serious disease in the wet rice-growing areas of Sri Lanka. No suitable chemicals for its control have been recommended. Since a variety resistant to ShB has yet to be found, the effectiveness of some fungicides was tested in vitro and in vivo. Ten concentrations, 10-100 ppm were tested against R. solani in PDA medium using the filter paper disc technique. The medium in the plates was divided into four equal parts and filter paper discs dipped in fungicide solutions were placed in each quarter. A single sclerotium of R. solani was placed in the center of the plate. The inhibition zone around each disc for each concentration was measured as the fungus grew. Benomyl, triphenyltin hydroxide, and pencycuron were used for field tests for two seasons in a randomized complete block design with three replications. Plot size was 6 x 3 m. Rice variety BW 288-1-3 was broadcast. Recommended fertilizers were applied. Standard plant protection measures were taken. The inoculum, 7-d-old R. solani cultured on rice grain was spread evenly on the water surface at panicle initiation. Fungicides were sprayed 24 h and 2 wk after inoculation at 0.5 kg ai/ha for benomyl and triphenyltin hydroxide and 0.25 kg ai/ha for pencycuron. Of fungicides tested in PDA medium, inhibitory zones were shown only with triphenyltin hydroxide at 10 ppm and pencycuron at 30 ppm. In both seasons, the lowest disease incidence was with pencycuron applied 24 h after inoculation
ShB [sheath blight] caused by Rhizoctonia solani Kuhn (Thanatephorus cucumeris) is a serious disease in the wet rice-growing areas of Sri Lanka. No suitable chemicals for its control have been recommended. Since a variety resistant to ShB has yet to be found, the effectiveness of some fungicides was tested in vitro and in vivo. Ten concentrations, 10-100 ppm were tested against R. solani in PDA medium using the filter paper disc technique. The medium in the plates was divided into four equal parts and filter paper discs dipped in fungicide solutions were placed in each quarter. A single sclerotium of R. solani was placed in the center of the plate. The inhibition zone around each disc for each concentration was measured as the fungus grew. Benomyl, triphenyltin hydroxide, and pencycuron were used for field tests for two seasons in a randomized complete block design with three replications. Plot size was 6 x 3 m. Rice variety BW 288-1-3 was broadcast. Recommended fertilizers were applied. Standard plant protection measures were taken. The inoculum, 7-d-old R. solani cultured on rice grain was spread evenly on the water surface at panicle initiation. Fungicides were sprayed 24 h and 2 wk after inoculation at 0.5 kg ai/ha for benomyl and triphenyltin hydroxide and 0.25 kg ai/ha for pencycuron. Of fungicides tested in PDA medium, inhibitory zones were shown only with triphenyltin hydroxide at 10 ppm and pencycuron at 30 ppm. In both seasons, the lowest disease incidence was with pencycuron applied 24 h after inoculation
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