Toxicity and Control Efficacy of Azoxystrobin against Potato Early Blight Alternaria solani

Sixty-three strains of Alternaria solani, a causal agent of potato early blight, were isolated from leaves of potato plants growing in major regions of potato production in northern southwest China with tissue isolation method. The sensitivity of thirty isolates among them to azoxystrobin was detected by conidial germination method. The results showed that all of them were highly sensitive to azoxystrobin, mean EC50 values of A. solani strains from Ankang in Shaanxi, Enshi in Hubei, Xichang in Sichuan to azoxystrobin were 0.024 4, 0.025 6 and 0.037 6 mg/L respectively, and the average EC50 value of all these strains was 0.029 0mg/L. In the field trial, the control efficacy of azoxystrobin 25% SC applied at the rate of 450 g/hm2 against potato early blight was 84.71% and compared with that of tebuconazole 43% SC applied at the rate of 300g/hm2, the difference was not significant; however, its control efficacy was significantly higher than those of the fungicides carbendazim 50% WP applied at the rate of 1500 g /hm2 and mancozeb 80% WP applied at the rate of 3000 g /hm2. Moreover, its application increased the yield markedly. So azoxystrobin could be used as a preferred pharmaceutical for controlling potato early blight in the region.