Persistence of α-Cypermethrin in Cabbage and Monocrotophos in three Soils of West Bengal

In a field trial to evaluate the persistence of a-cypermethrin, cabbage crop was sprayed with 30.45 and 60g a.i. ha⁻¹ resulting in corresponding initial deposits of 0.349, 0.565 and 0.736 ppm in cabbage head and 0.110,0.170 and 0.228 ppm in the cropped soil respectively. Residues readily dissipated and went beyond detection on 20 d after application in cabbage head and 10 d in cropped soil samples irrespective of the treatment dose. Calculated half-lives and safe waiting periods of the insecticide in cabbage head ranged from 1.956–2.105 and 3.594–5.269 d respectively. Persistence of monocrotophos was also studied in red laterite (Bolpur), saline alkali (Bokkhali) and neutral to slightly alkaline (Mondouri) soils both under non-flooded and flooded conditions maintained in the laboratory. Soil samples were fortified with a single dose of 1600 ppm and the highest rate of dissipation was found in Bokkhali soil followed by Mondouri and Bolpur soils. Calculated half-lives for monocrotophos were lower in flooded soils (5.90–8.36 d) with the lowest in flooded Bokkhali soil (5.90 d).