Objective Sensitivity of Magnaporthe oryzae to pyraclostrobin was determined with control efficacy of the fungicide on rice plants tested at the coastal farming areas in Liaoning Province.

Method In vitro pyraclostrobin sensitivity of 113 single spore-derived strains of M. oryzae isolated from the diseased LTH rice in 2025 was determined. Toxicity of the commercially available Pyraclostrobin EC at the application rate of 250 g·L⁻¹ on 15 single spore-derived strains of infected Yanfeng 47 rice were tested in laboratory using the mycelium growth rate method. Subsequently, efficacy of the fungicide product at varied application doses was examined in the field.

Result The EC₅₀ of M. oryzae to pyraclostrobin in various concentrations ranged from 0.03×10⁻³ μɡ·mL⁻¹ to 34.45×10⁻³ μɡ·mL⁻¹. Since the data were in a single peak, normal distribution, the mean of 4.29×10⁻³ μɡ·mL⁻¹ was taken as the baseline to classify 98.23% of the strains in fungicide-sensitive and 1.77% in low-resistant categories. The virulence of Pyraclostrobin EC applied at 250 g·L⁻¹ on the pathogens was shown with EC₅₀ at 1.01×10⁻³-89.33×10⁻³ μɡ·mL⁻¹ (averaging 25.52×10⁻³ μɡ·mL⁻¹) and EC₉₀ at 1.18-115.87 μɡ·mL⁻¹ (averaging 21.39 μɡ·mL⁻¹). In the field, the efficacy of 250g·L⁻¹ Pyraclostrobin EC and 75% Triadimefon WP in controlling the leaf blast were 89.77% and 91.66%, respectively, and in treating the panicle neck blast 93.82% and 91.48%, respectively.

Conclusion Application of Pyraclostrobin EC at 250g·L⁻¹ could effectively control both leaf and panicle neck blast on rice plants without apparent drug-resistance. It seemed adequate for the use on rice farming in the area.