Persistence and Dissipation Pattern of Dimethoate 30 EC in / on Foxtail Amaranthus and Spinach


                                A survey was conducted to know the insecticide usage pattern in leafy vegetables and found that dimethoate was the most frequently used insecticide. A field trail was conducted to know the dissipation pattern of dimethoate in foxtail amaranthus and spinach during October - November, 2017. Dimethoate 30 EC was sprayed twice as foliar treatment at 10 days interval @ 200 and 400 g a.i ha-1. The samples were collected from 0, 1, 3, 5, 7, 10, 15 and 20 days after treatment (DAT), extracted by modified QuEChERS method and analyzed by LCMS. The mean initial deposit (1 h after spraying) of dimethoate at 200 and 400 g a.i ha-1 were 7.25 μg g-1 and 19.51 μg g-1 for foxtail amaranthus and 18.37 μg g-1 and 29.46 μg g-1 for spinach, respectively. The residues reached below detectable level of 0.05 μg g-1 at 10 days after treatment in foxtail amaranthus and 15 and 20 DAT in spinach for both doses. Half-life of dimethoate residues were 0.85 and 0.86 days in foxtail amaranthus; 2.22 and 1.12 days in spinach at 200 and 400 g a.i ha-1, respectively.

Key words : Foxtail amaranthus, Spinach, Dimethoate, QuEChERS, LCMS.