Sensitivity of Bipolaris maydis to iprodione and pyraclostrobin and their control efficacy against southern corn leaf blight in Fujian province

To determine the sensitivity of Bipolaris maydis to dicarboximide (DC) and quinone outside inhibitor (QoI) fungicides, and evaluate their control efficacy against southern corn leaf blight (SCLB), a total of 73 B. maydis isolates collected from seven regions in Fujian province of China were tested for their sensitivity to iprodione and pyraclostrobin (representative fungicides of DC and QoI families) using mycelial growth method. The results indicated that the tested isolates were very sensitive to iprodione and pyraclostrobin, and the EC50 value of these isolates to iprodione and pyraclostrobin were in the range of 0.168-2.990 and 0.017-6.583 μg/mL, with the mean value of (1.003±0.533) and (1.437±1.490) μg/mL, respectively. The frequency curves of iprodione and pyraclostrobin were continuous and unimodal, and followed the normal distribution. Hence, the mean EC50value of (1.003±0.533) and (1.437±1.490) μg/mL can be recognized as baseline sensitivities of B. maydis to iprodione and pyraclostrobin, respectively. Results of field trials showed that two sprays of 50% iprodione SC at 750 g a.i./hm2 and 25% pyraclostrobin EC at 150 g a.i./hm2 exhibited high efficacy for the control of SCLB, with the control efficacies ranging of 61.51%-70.69% and 69.54%-78.98%, respectively. These efficacies were as good as twice spray of 25% propiconazole EC at 150 g a.i./hm2, and significantly higher than the efficacies of reference fungicides 75% chlorothalonil WP at 1 875 g a.i./hm2 and 80% mancozeb WP at 2 000 g a.i./hm2. This study will guide the reasonable selection of fungicides for effective management of SCLB, and the resistance risk assessment and monitoring of B. maydis in the future.