Comparative persistence of flubendiamide residues in gherkin and soil under different environmental conditions

Abstract

Flubendiamide is used for control of gherkin fruit borer which is a major insect pest. Its application may result in residue levels in gherkin above the safe limits at harvest. Environmental conditions may have effect on the residue persistence of flubendiamide on gherkin. Studies were conducted to evaluate the residue persistence of flubendiamide on gherkin at 2 locations (Bangalore and Dharwad) after spray applications at 60 and 120 g a.i./ha. QuEChERS method in conjunction with HPLC was used for analysis of flubendiamide. The method was validated by studying parameters such as recovery, limit of detection (LOD), limit of quantification (LOQ), linearity, accuracy, precision and measurement uncertainty (MU). Recovery of flubendiamide and des-iodoflubendiamide from gherkin and soil was in a range of 96.3-100.4% with relative standard deviation (RSD) within 3.2-7.8% and MU, 10.0-15.3%. The LOQ of both compounds was 0.01 mg/kg. Initial residues of flubendiamide were 2.246 and 3.382 mg/kg at Bangalore; 2.003 and 2.982 mg/kg at Dharwad from treatments at 60 and 120 g a.i./ha, respectively. Flubendiamide degraded with the half-life of about 2 days at both locations. The pre-harvest intervals (PHIs) were 7 and 9.7 days at Bangalore; 6.3 and 8.1 days at Dharwad. The metabolite, des-iodoflubendiamide was not detected in gherkin. Field soil was free from residues on the 15th day at both locations. Flubendiamide application should be given at early stage of the crop growth to allow residues to dissipate to the safe levels and environmental conditions may not have significant effect on its residue persistence.