Residue evaluation of imidacloprid, spirotetramat, and spirotetramat-enol in/on grapes (Vitis vinifera L.) and soil

Abstract

A combination of imidacloprid and spirotetramat effectively controls sucking pests on grapevines. Residues of these insecticides on grapes were evaluated after treatment with spirotetramat 12 % + imidacloprid 12 % (240 SC) three times at 90 and 180 g a.i. ha⁻¹. The samples were extracted and purified by QuEChERS method and analyzed by high-performance liquid chromatography with a photodiode array detector (imidacloprid) and gas chromatography mass spectrometry (spirotetramat and its metabolite spirotetramat-enol). Satisfactory results were obtained with ranges of 80.6–98.6 % for the recovery, 3.1–10 % for the relative standard deviation range, and 9.8–15.6 % for the uncertainty. The limits of detection and quantification were 0.015 μg mL⁻¹ and 0.05 mg kg⁻¹, respectively. Initial residue concentrations of imidacloprid after the 90 and 180 g a.i. ha⁻¹ treatments were 0.912 (half-life 11 days) and 1.681 mg kg⁻¹ (half-life 12.4 days), respectively. For spirotetramat + spirotetramat-enol, the residue concentrations were 1.337 (half-life 5.6 days) and 2.0 mg kg⁻¹ (half-life 7.6 days) for the 90 and 180 g a.i. ha⁻¹ treatments, respectively. Spirotetramat degraded faster than spirotetramat-enol. After treatment at 90 g a.i. ha⁻¹, the initial residues of both insecticides were within European Union maximum residue limits and a 1-day pre-harvest interval (PHI) was adequate for safe consumption of grapes. After treatment at 180 g a.i. ha⁻¹, the required PHI was 7 day. Therefore, a PHI of 7 day should be used after treatment with imidacloprid and spirotetramat.