Dissipation behaviour of spinosad in polyhouse grown tomato under mid-hill conditions of Himachal Pradesh, India.

An established analytical method was further standardized for the estimation of spinosad residue in tomato grown under naturally ventilated polyhouse situated in mid-hills of Himachal Pradesh, India. Spinosad was sprayed on hybrid tomato cv. Avtar at the recommended and double the recommended dosages at 15 and 30 g a.i. ha(-1), respectively, to control the lepidopterous pests and the residue were analysed from tomato fruits at different intervals after second spray. The samples were extracted with acetonitrile-water mixture (8:2), partitioned into dichloromethane, methanol and anhydrous sodium hydroxide. The extracts were concentrated under vacuum and cleaned up with silica solid phase extraction cartridge. Further, the samples were analysed in high-performance liquid chromatography equipped with UV/visible detector at λ = 250 nm and C18 reversed-phase column. Consistent recoveries ranging from 80.6 ± 1.1 to 91.4 ± 1.2 % were observed when samples were spiked at fortification range of 0.01 to 0.20 mg kg(-1). The limit of quantification of the method was worked out to be 0.02 mg kg(-1). The half-life values of spinosad were determined to be 1.20 and 1.60 days at recommended and double the recommended dosage, respectively. The safety interval for spinosad sprayed tomato fruit was determined to be 1.92 and 3.88 days at application rate of 15 and 30 g a.i. ha(-1), respectively.