Dissipation Studies of Bifenthrin and Dimethoate in Tea [Camellia sinensis (L.) O. Kuntze]

Bifenthrin at three different concentrations viz., 40, 60, 80 g a.i./ha with dimethoate at 450 g a.i./ha (standard check) were evaluated against tea mosquito bug, Helopeltis theivora and studied their dissipation pattern in green tea leaves. The initial deposits were estimated as 0.162, 0.263, 0.345 and 1.23 µg g⁻¹ for bifenthrin at 40, 60, 80 g a.i./ha and dimethoate at 450 g a.i./ha respectively. The residues of bifenthrin 40 g (0.025 µg g⁻¹) and 60 g (0.050 µg g⁻¹) could be detectable only up to 3^rd day of spraying while residues of bifenthrin 80 g and dimethoate 450 g a.i./ha persisted up to 7^th and 15^th d of application. The half life of bifenthrin at 40, 60 and 80 g a.i./ha, in tea leaves was 1.17,1.17 and 1.90 d respectively and 3.38 d for dimethoate 450 g a.i./ha. A waiting period of 3 days for bifenthrin and 7 days for dimethoate have been suggested.