Dynamic Degradation of Four Herbicides in Soil and Phytotoxicity to Chili and Tobacco.

Herbicide carryover from wheat production can injure sensitive rotational cash crops, but compound-specific replanting guidance under matched soil and climatic conditions is limited. We combined an optimized QuEChERS method with ultra-high performance liquid chromatography to quantify soil residues of mesosulfuron-methyl, pyroxsulam, diflufenican, and pyroxasulfone and evaluate the phytotoxicity of these herbicides to rotational chili and tobacco. The recoveries of the four herbicides at 0.1-1 mg/kg spiking levels ranged from 74.42 to 117.33%, which fell within the acceptable recovery range for residue analysis, with RSDs less than 6.69%. The results of field experiments demonstrated that the half-lives of pyroxsulam, mesosulfuron-methyl, pyroxasulfone, and diflufenican were 9.4, 22.7, 113.6, and 203.8 days, respectively. The bioassays indicated that GR50 of these herbicides on chili were 0.084, 0.116, 0.041, and 3.986 mg/kg, respectively. Similarly, the GR50 of these herbicides on tobacco were 0.035, 0.128, 0.014, and 4.146 mg/kg, respectively. The safe intervals for the cultivation of chili and tobacco should exceed 3 months following the application of pyroxsulam and mesosulfuron-methyl. However, owing to the prolonged residual periods of pyroxasulfone and diflufenican in the soil, it is necessary to establish a safe planting interval for chili and tobacco that exceeds 24 months. This study provides a theoretical foundation for determining safe replanting practices for chili and tobacco as rotational crops following wheat field application of the four tested herbicides.