Abstract: The effect of three carboxylic acid amides fungicides on different life stages of Phytophthora melonis was investigated.The results indicated that flumorph,dimethomorph and iprovalicarb could effectively inhibit cystospore germination (with EC50 values of 0.54,0.46,0.34 μg/mL,respectively),mycelial growth (with EC50 values of 0.92,0.70,0.67 μg/mL,respectively) and sporangia production (with EC50 values of 0.48,0.31,0.26 μg/mL,respectively) of P.melonis.But they had no effect on the zoospores release,zoospore motility and the formation of cystospore.The mean EC50 values of flumorph,dimethomorph and iprovalicarb to mycelium growth of P.melonis strains isolated from fields were 1.09(±0.24),0.29(±0.04),and 0.32(±0.07) μg/mL,respectively.And the baseline sensitivities of the three fungicides were distributed as unimodal curves.No resistant subpopulation was detected among these strains.