Bioactivitiy of Fungicides to Metalaxyl Resistant Isolate of Phytophthora infestans

The bioactivity of several fungicides to metalaxyl resistant isolate TZ25 of Phytophthora infestans was studied. The results showed that azoxystrobin, fluazinam, infinito (6.25% fluopicolide + 62.5% propamocath) and propineb gave strong fungistatic actions against TZ25. Their EC50 values to mycelial growth of TZ25 were 0.0225, 0.1560, 0.9085 and 4.3665 mg/L, respectively, and to sporangia germination were 0.0301, 0.1378, 0.4143 and 2.0445 mg/L, respectively. There was no cross resistance between metalaxyl and azoxystrobin, fluazinam, or infinito. The results of pot culture experiments indicated that azoxystrobin, fluazinam and infinito were effective for the control of tomato late blight caused by TZ25, and their control effects were 86.76, 82.15 and 85.20%, respectively.