Toxicity Test of Ten Fungicides to Phytophthora infestans in Laboratory

The toxicity of 10 fungicides against Phytophthora infestans was detected by the method of mycelium growth inhibition.The results showed that 50% dimethomorph WP had the best control effect with EC50 and EC90 as 1.81 μg/ml and 10.63 μg/ml respectively,and the regression equation was Y=4.57272+1.66462X.The followed fungicides were 250 g/L azoxystrobin SC and 75% chlorothalonil WP with the EC50 as 2.70 μg/ml and 2.54 μg/ml,and the EC90 as 1.08×107 μg/ml and 10 708.95 μg/ml respectively.But with the increase of dosage,the control effects of the two fungicides did not increase significantly,and their EC90 value were higher.The control effects of 58% metalaxyl·mancozeb WP and 70% metiram WDP were relatively higher with the EC50 value as 6.09 μg/ml and 8.75 μg/ml,and the EC90 as 69.98 μg/ml and 60.19 μg/ml respectively.Their regression equations were Y=4.05225+1.20831X and Y=3.55894+1.52997X respectively.25% carbendazim WP also could inhibit Phytophthora infestans.Although the extended area of hypha was great,the hypha grew weak and thin.