Persistence and Dissipation of Imidacloprid and Bifenthrin on Rapeseed Leaves

Dissipation behaviour of imidacloprid and bifenthrin applied underfield condition on Brassica campestris, rapeseed crops was studied in tender shoots and seeds. The initial deposits of imidacloprid at 20, 40, 60 g a.i ha⁻¹, bifenthrin at 60, 80,100g a.i ha⁻¹and deltamethrin at 15g a.i ha⁻¹ were 0.830,1.126,1.280,0.446, 0.666, 1.448 and 1.478. respectively. Imidacloprid residues reached below its detectable level after 5^th and 10^th day of its application at lower and higher rates. The half life values were 1.44, 1.96, 1.67, 1.17, 1.36, 1.43 and 1.51 days for imidacloprid at 20, 40, 60 g a.i ha⁻¹, bifenthrin at 60, 80, 100 g a.i ha⁻¹ and deltamethrin at 15 g a.i ha⁻¹, respectively. Based on the observations, a waiting period of at least four days after imidacloprid application at recommended dose (20 g a.i ha⁻¹) is suggested and considered safe from point of health hazards due to toxic effect of residues in leaves.