Biological activity of different fungicide controlling tobacco black shank

Effects of fungicides dimethomorph,azoxystrobin,kresoxim-methyl,metalaxyl and mancozeb on mycelial growth,sporulation,zoospores release and germination of sporangia as well as of cystospores of Phytophthora parasitica were studied.Results showed that dimethomorph and metalaxyl inhibited mycelial growth more effectively than other fungicides tested in order of mancozeb,azoxystrobin,kresoxim-methyl.Sporangia production was reduced by dimethomorph and metalaxyl more than by azoxystrobin,kresoxim-methyl or mancozeb.Zoospore release from sporangia was most sensitive to azoxystrobin and kresoxim-methyl,less sensitive to mancozeb and insensitive to dimethomorph and metalaxyl.Direct germination of sporangia of P.parasitica was inhibited by azoxystrobin and kresoxim-methyl,followed by dimethomorph and mancozeb,whilst was insensitive to metalaxyl.Germination of encysted zoospores of P.parasitica was most sensitive to azoxystrobin and kresoxim-methyl,followed by dimethomorph.Mancozeb was moderately active,while metalaxyl showed no effects.