Concentrations and dissipation of difenoconazole and fluxapyroxad residues in apples and soil, determined by ultrahigh-performance liquid chromatography electrospray ionization tandem mass spectrometry

Abstract

A new combined difenoconazole and fluxapyroxad fungicide formulation, as an 11.7 % suspension concentrate (SC), has been introduced as part of a resistance management strategy. The dissipation of difenoconazole and fluxapyroxad applied to apples and the residues remaining in the apples were determined. The 11.7 % SC was sprayed onto apple trees and soil in Beijing, Shandong, and Anhui provinces, China, at an application rate of 118 g a.i. ha⁻¹, then the dissipation of difenoconazole and fluxapyroxad was monitored. The residual difenoconazole and fluxapyroxad concentrations were determined by ultrahigh-performance liquid chromatography tandem mass spectrometry. The difenoconazole half-lives in apples and soil were 6.2–9.5 and 21.0–27.7 days, respectively. The fluxapyroxad half-lives in apples and soil were 9.4–12.6 and 10.3–36.5 days, respectively. Difenoconazole and fluxapyroxad residues in apples and soil after the 11.7 % SC had been sprayed twice and three times, with 10 days between applications, at 78 and 118 g a.i. ha⁻¹ were measured. Representative apple and soil samples were collected after the last treatment, at preharvest intervals of 14, 21, and 28 days. The difenoconazole residue concentrations in apples and soil were 0.002–0.052 and 0.002–0.298 mg kg⁻¹, respectively. The fluxapyroxad residue concentrations in apples and soil were 0.002–0.093 and 0.008–1.219 mg kg⁻¹, respectively. The difenoconazole and fluxapyroxad residue concentrations in apples were lower than the maximum residue limits (0.5 and 0.8 mg kg⁻¹, respectively). An application rate of 78 g a.i. ha⁻¹ is therefore recommended to ensure that treated apples can be considered safe for humans to consume.