In order to define the sensitivity sensitivity of Magnaporthe oryzae to prochloraz and tricyclazole and the synergistic effect of two agents,the 103 isolates of M.oryzae were isolated and collected from Guizhou,Hubei,Henan and Hunan Provinces,sensitivity of M.oryzae isolates to prochloraz was determined by mycelial growth rate method,rice seedling method was used to determine the sensitivity of M.oryzae to tricyclazole and the synergistic effect of prochloraz and tricyclazole.The results showed that the EC₅₀ of prochloraz,tricyclazole against M.oryzae were 0.004 2—0.056,0.35—9.67 μg/mL,respectively,and the sensitivity frequency distribution of strain was close to normal distribution.Thus,the average EC₅₀ values 0.027,5.24 μg/mL could be used as basline-sensitivity of M.oryzae to prochloraz,tricyclazole in the southern region of China,respectively.The results of synergistic combination showed that the ratio of obviously effective components of prochloraz to tricyclazole was 4∶20,the co toxicity coefficient(CTC) was 177.10 and EC₅₀ value was 1.10 μg/mL.After 21 d after treatment the field efficacy of this combination(4∶20) of 180 g/ha was 86.41% against rice blast.Thus,the prochloraz and tricyclazole(4∶20)can be applied to control rice blast in field production,and the recommended dosage should be 180 g/ha.