SCREENING OF FUNGICIDES FOR CONTROLLING PHYTOPHTHORA ROOT ROT OF SOYBEAN

Effect of 8 systemic fungicides on growth of Phytophthora sojae was investigated in vitro. Among the tested chemicals, seven of them effectively inhibit the groth of P.sojae except propamocarb hydrochloride. The EC 50 values for inhibition of mycelial growth by metalaxyl, dimethomorph mancozeb, metalaxyl mancozeb, oxadixyl mancozeb, cymoxanil mancozeb, curzate-M8 were 0.4870 μg/mL, 1.4261 μg/mL, 1.7697- μg/mL, 11.0996 μg/mL, 10.2114 μg/mL and 8.0294 μg/mL respectively. Metalaxyl had the lowest EC 50 value and exhibited highest inhibitory action to P. sojae. In vivo, metalaxyl and metalaxyl mancozeb completely inhibit the infection of P. sojae to susceptible soybean cultivar, and the efficacy lasted for a longer; In addition dimethomorph mancozeb, oxadixyl mancozeb and propamocarb hydrochloride had better controlling efficacy, however, they had short time of action. The sensitivity of 15 isolates of P. sojae from different locations to metalaxyl mancozeb was tested, no tolerant isolate was found. At present, the resistant to Phytophthora soybean cultivars are not available, applying metalaxyl mancozeb to control this disease may be an alternative and effective way.