Residue dynamics of tebuconazole and quinalphos in immature onion bulb with leaves, mature onion bulb and soil.

Residue persistence of tebuconazole and quinalphos in immature onion bulb with leaves (spring onion), mature onion bulb and soil was studied following their spray applications 3 times. The applications were untreated control; tebuconazole @ 187.5 and 375 g a.i. ha(-1); quinalphos @ 300 and 600 g a.i. ha(-1). Initial residue deposits of tebuconazole in immature onion bulb with leaves from the two treatments were 0.628 and 1.228 mg kg(-1). The residues of tebuconazole dissipated with the half-life of 5 and 7.7 days. The safe pre-harvest intervals (PHI) for consumption of immature onion bulb with leaves were 16 and 35 days, respectively. Initial residue deposits of quinalphos in immature onion bulb with leaves from the two treatments were 0.864 and 2.283 mg kg(-1). Loss of quinalphos residues from immature onion bulb with leaves was very fast. The residues dissipated with the half-life of 1.7 and 2.6 days and the required PHI was 5 and 11 days, respectively. At harvest mature onion bulbs were free from residues of both tebuconazole and quinalphos.