Objective  The sensitivity of Phomopsis asparagi to difenoconazole, and the disease control efficacies of 3 fungicide products in the field were studied.

  Method  Pathogen samples of the stem blight disease on asparagus were collected from Fujian, Henan, Hunan, Shanxi, and Shandong provinces and isolated to determine their mycelial growth on a medium laden with difenoconazole. The disease control efficacies of 3 fungicide products, i.e., (a) 10% difenoconazole WG, (b) 35% fluopyram+tebuconazole SC, and (c) 325 g·L^-1 difenoconazole+azoxystrobin SC, were assessed in the field.

  Result  The EC₅₀ of the 132 isolates to difenoconazole ranged between 0.010 8 μg·L^-1 and 2.654 8 μg·mL^-1 averaging (0.693 4±0.044 1)μg·mL^-1. The data did not exhibit a normal distribution pattern. A significant difference in difenoconazole sensitivity was found between the isolates from Fujian and Shandong or Hunan (P < 0.05). Even the pathogen samples from a same province varied in their sensitivity toward the fungicide. The field test demonstrated that when (a) was applied at 135.00 g·hm^-2 the disease severity was reduced by 75.60% in 2017 and 75.91% in 2018; when (b) was employed at 118.13+118.13 g·hm^-2 the severity was lessened by 82.08% in 2017 and 82.32% in 2018; and, when (c) was used at 84.38+135.00 g·hm^-2 the severity was decreased by 82.74% in 2017 and 83.23% in 2018. It indicated that the latter two applications were significantly more effective than the first one for the disease control (P < 0.05).

  Conclusion  The non-normal distribution of the sensitivities to difenoconazole of the pathogen isolates from various localities suggested the existence of resistant subpopulations of P. asparagi in the field. Being safe to Asparagus officinalis, the application of either 35% fluopyram+tebuconazole SC or 325 g·L^-1difenoconazole+azoxystrobin SC was recommended for the control of stem blight disease on asparagus.