Sensitivity baseline to pydiflumetofen in Passalora fulva and control efficacy of pydiflumetofen against tomato leaf mold

Pydiflumetofen is a novel succinate dehydrogenase inhibitor (SDHI), which shows excellent inhibitory activity to many plant pathogens, such as Fusarium graminearum and Sclerotinia sclerotiorum. In this study, the sensitivity to pydiflumetofen of Passalora fulva strains collected from 8 cities in Shandong Province were tested by using mycelial growth rate method. In addition, the control efficacy of pydiflumetofen to tomato leaf mold were also investigated in field. The results showed that pydiflumetofen had strong inhibitory activity on three developmental stages of P. fulva, and the inhibitory activities on spore gemination and germ tube elongation were higher than that on mycelial growth. Inhibition rate of pydiflumetofen to spore gemination and germ tube elongation of P. fulva was over 50% at 0.10 μg/mL. The EC₅₀ values frequency distribution of 103 P. fulva isolates to pydiflumetofen on mycelial growth was a unimodal curve and could be regarded as the baseline sensitivity. The EC₅₀ values ranged from 0.04 to 1.74 μg/mL, with a mean of (0.67 ± 0.41) μg/mL. In field trials of two years, after the last application at the dose of 200 g a.i./hm², the control efficacy of pydiflumetofen was above 80%, which was significantly higher than that of thiophanate-methyl (540 g a.i./hm²) and fluopyram (150 g a.i./hm²). This study provides data support for monitoring the resistance of tomato leaf mold to pydiflumetofen and for efficient controlling tomato leaf mold.