In order to screen the effective agents to control the tobacco Corynespora leaf spot, in this study, the mycelial growth rate method was employed to determine the toxicity of ten fungicides(98% of Dimethachlon, 95% of fluazinam, 98% of difenoconazole, 97% of propiconazol, 95% of pyraclostrobin, 96% of Ametoctradin, 96% of iprodione, 98% of azoxystrobin, 95% of kresoximmethyl, and 98% of prochloraz) on the mycelial growth of three Corynespora cassiicola strains, namely DWZ, WZ-16, and WZ-45. Meanwhile, the field control effect of 10 kinds of fungicides(200 g/L of Pydiflumetofen·Difenoconazole SC, 40% of Dimethachlon WP, 3% of Zhongshengmycin WP, 20% of Thiodiazole copper SC, 50% of fluazinam WP, 50% of chloroisobromine-cyanuric-acid WP, 57.60% of Cu(OH)2 WDG, 25% of prochloraz EC, Bacillus amyloliquefaciens LB21 AS, and Bacillus velezensis MH24 AS) on tobacco Corynespora leaf spot was measured. The results showed that 10 fungicides showed different bacteriostatic activity against mycelium growth of 3 strains of tobacco Corynespora leaf spot pathogenic fungi. The bacteriostatic activity in the descending order was prochloraz(0.23 mg/L), fluazinam(0.23 mg/L), difenoconazole(0.4 mg/L), pyraclostrobin(1.05 mg/L), propiconazol(1.06 mg/L), iprodione(1.08 mg/L), dimethachlon(3.76 mg/L), azoxystrobin(5.22 mg/L), kresoxim-methyl(18.03 mg/L), and Ametoctradin(200.25 mg/L). The results of the field trials showed that there were differences in the control effect of the 10 agents. The field control effect of 200 g/L of Pydiflumetofen·Difenoconazole SC was the best, it was 79.51% after 12 days of application. Followed by 20% of Thiodiazole copper SC and 50% of fluazinam WP, their relative control effect was 69.75% and 68.47%, respectively. In conclusion, it was recommended to use 200 g/L of Pydiflumetofen·Difenoconazole SC at the recommended dose of 600 mL/ha for field control of tobacco Corynespora leaf spot.
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