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Distribution, Residue Dynamics, and Insecticidal Efficacy of Trunk-Injected Emamectin Benzoate in Pecan Trees

Zhi Liang,Xi Zhou,Yinlong Li,Min Zhou,Xutao Yang,Shengnan Zhang,Jacob D. Wickham,Qing-He Zhang,Longwa Zhang

Carya illinoinensis(Wangenh.) K. Koch (Pecan), a deciduous tree native to North America, faces significant challenges from pests. This study investigated the insecticidal efficacy and food safety of using the broad-spectrum insecticide emamectin benzoate via trunk injection for potential pecan pest management. Injections were given at dosages of 0.4, 0.8, 1.6, and 2.4 mL/cm of tree diameter at breast height (DBH), and leaf samples were collected at 10, 30, 60, and 100 days post-injection, while fruit samples were obtained during the swelling, ripening, and harvest stages. We established an analytical method for the determination and quantification of emamectin benzoate content in pecans using ultra-performance liquid chromatography–mass spectrometry (UPLC-MS). Leaf emamectin benzoate content was significantly higher compared to nuts (p≤ 0.036). The content in leaves following the four dosage treatments decreased over time and at 100 days was 0.1943/0.2799 mg/kg (upper crown/lower crown), 0.1910/0.3957 mg/kg, 0.3663/0.6235 mg/kg, and 1.3988/1.9123 mg/kg, respectively. The pesticide residues of 0.4 mL/cm and 0.8 mL/cm treatment groups in kernels at harvest time were 0.0016 mg/kg and 0.0039 mg/kg, respectively, below the latest European Union Regulation (0.005 mg/kg). All four dosage treatments (0.4, 0.8, 1.6, and 2.4 mL/cm of tree diameter at DBH) in the leaf feeding test caused significant mortalities of the fourth instarHyphantria cunea(Drury) larvae. The mortality rates at 10 days post-injection were 64.7%, 73.3%, 79.3%, and 84.7%, respectively, while at 60 days post-injection, the rates were 26.0%, 47.3%, 53.7%, and 81.7%, respectively. In summary, this study successfully established a sensitive analytical method for the detection and quantification of trunk-injected emamectin benzoate residues in pecans and demonstrates its safety and effectiveness as a chemical control option against foliar pecan pest insects.