Studies on Dissipation Pattern and Bioefficacy of Combination Product, Spirotetramat 120 SC +Imidacloprid 120 SC against Onion Thrips, Thrips tabaci Lindeman during Rabi Season

Abstract

Studies on bioefficacy of seven insecticides were evaluated by adopting good agriculture practices against onion thrips. First application was done as incidence of thrips was observed at 35 days after transplanting and subsequent applications were given at an interval of 10 days. Population of thrips was recorded on five randomly selected plants in each plot. While, for dissipation studies three applications of insecticide given at an interval of seven days starting at 45 days before harvesting @ 75 g a.i./ha (recommended dose) and 150 g a.i./ha (Double the recommended dose). QuChERs method used for residue analysis and quantification of samples by using High Performance Liquid Chromatography. Out of seven insecticides fipronil 30 a.i./ha proved to be most effective insecticide, also the combination of spirotetramat + imidacloprid was effective against onion thrips. In case of residue study the initial residues of spirotetramat (0.51 and 0.97 mg/kg) and imidacloprid (0.69 and 1.43 mg/kg) reached below quantification limit on 5th and 7th day at recommended and double the recommended doses, respectively. Half-life values for spirotetramat were 1.63 and 2.01 days while, for imidacloprid 1.63 and 1.56 days at recommended and double the recommended doses, respectively. Whereas, soil collected at harvest, did not record any residues of spirotetramat, spirotetramat-enol and imidacloprid at both the doses. Evaluating the assessment of insecticides, fipronil @ 30 g a.i./ha was proved to be highly effective by consistently suppressing the thrips population (3.26 thrips/plant & 86.62 % reduction over control). Considering LOQ of 0.05 mg/kg for spirotetramat and imidacloprid pre harvest interval (PHI) of seven days can be recommended for consumer safety.