Abstract: To investigate the effects of Phytophthora nicotianae to flumorph and delay the development of its flumorph resistance, the sensitivity of P. nicotianae to flumorph was determined by a colony growth rate method. In addition, the effects of Phytophthora nicotianae on a combinatory fungicide (flumorph + metalaxyl) were evaluated by the Wadley method. The combination ratio of the fungicide with a high antibacterial activity was selected and the synergistic effects of the flumorph and metalaxyl combination and Bacillus amyloliquefaciens ZY-9-13 were evaluated by the Abbott model. The results showed that the EC₅₀ values of 71 strains of P. nicotianae to flumorph ranged from 0.428 5 to 0.760 8 μg/mL with a mean of 0.588 4 μg/mL. The sensitivity distribution was unimodal, and there was no resistant isolate in the 71 strains. The additive effect of the combinatory fungicide at a volume ratio of 1:10 was the most effective (EC₅₀=0.398 7 μg/mL). The growth of B. amyloliquefaciens was not affected by the fungicide. The combined application of the fungicide at different concentrations and ZY-9-13 (10¹⁰ cfu/mL) had better inhibitory effects comparing with a single application of each fungicide, and there existed a synergistic effect between them.