Bioactivities of boscalid, etc. eight fungicides against the pathogen of tobacco leaf spot

Bioactivities of eight fungicides (boscalid, difenoconazole, propiconazole, flusilazole, carbendazim, prochloraz, dimethachlon, mancozeb) to the pathogen of a tobacco leaf spot, Didymella segeticola, were determined using bioassay method at the mycelial growth stage. In vivo protective and curative effects of these fungicides against D. segeticolla on detached tabbaco leaves were also analyzed. The results showed that eight fungicides exhibited different inhibitory activities against mycelial growth of the pathogen, and also showed some protective and curative efficacies against the leaf spot. The most effecient one against mycelial growth of the pathogen was boscalid, with an EC₅₀ value of (0.0470 ± 0.0120) mg/L; followed by difenoconazole (0.0790 ± 0.0050) mg/L, prochloraz (0.29 ± 0.08) mg/L, propiconazole (0.69 ± 0.12) mg/L, dimethachlon (1.08 ± 0.33) mg/L, carbendazim (1.22 ± 0.29) mg/L, flusilazole (1.38 ± 0.07) mg/L; and most least effecient one was mancozeb with an EC₅₀ value of (22.80 ± 10.51) mg/L. Flusilazole, difenoconazole, propiconazole, boscalid and dimethachlon all had better protective activity for the control of this disease with >82% efficacy at 25 mg/L dosage treatment than 100 mg/L mancozeb showed 70.51% efficacy. Both boscalid and flusilazole showed better curative activities, with efficacies of >80% at 25 mg/L dosage treatment, followed by prochloraz, difenoconazole, carbendazim and dimethachlon; mancozeb showed relatively poor activity with 63.31% efficacy at 100 mg/L dosage treatment. The results provide scientific basis and reference for the screening of fungicides to control tobacco leaf spot.