Residues and Dissipation Dynamics of Four Herbicides in Alfalfa

SU Wangcang; NIU Yujia; LONG Yan; YAN Zhaoling; XUE Fei; SUN Lanlan; XU Hongle; WU Renhai

doi:10.15933/j.cnki.1004-3268.2025.09.013

Abstract：To clarify the residue behavior of imazapic,imazethapyr,carfentrazone-ethyl,and terbacil in alfalfa(Medicago sativa L.),a quantitative analytical method was established using LC-MS/MS.Field trials were conducted during the spring and summer of 2023 to characterize the degradation kinetics and final residues of these four herbicides in alfalfa.Results demonstrated that the method achieved limits of detection(LODs)ranging from 0.01 to 0.1 mg/kg for imazapic,imazethapyr,carfentrazone-ethyl,and terbacil in alfalfa.The average recovery rate fell within 83.8%—113.2%,with relative standard deviations(RSDs)all below 4.81%.These parameters confirmed the method's accuracy,precision,and suitability for pesticide residue analysis.The degradation of imazapic,imazethapyr,carfentrazone-ethyl,and terbacil in alfalfa followed first-order kinetics,with half-lives of 1.37-1.62,2.57-2.86,2.09-3.18,and 8.66-9.36 d,respectively.At harvest,residues were detected only in summer trials treated with imazethapyr at 150 g/ha(1.5×recommended high dosage),and terbacil at 432 g/ha(1.5×recommended high dosage).However,the detected residue levels for both compounds were below the corresponding United States Maximum Residue Limits(US MRLs).These findings indicate that imazapic,imazethapyr,carfentrazone-ethyl,and terbacil are readily degradable herbicides in alfalfa.Their application at normal rates is considered safe with respect to the residue levels at harvest.