Drift during center-pivot chemigation of chlorpyrifos with and without crop oil

Drift was measured during centor-pivot irrigation application of chlorpyrifos with and without crop oil. Insecticide quantities applied without crop oil were higher at 20 m than at other distances and declined as the distance from the pivot increased. Chlorpyrifos applied with crop oil drifted farther than when chemigated without crop oil, and the locations with the highest residue levels were in line with the airflow. Human exposures were estimated for the residue levels and drift patterns detected, indicating great potential for human exposure downwind from a chemigation operation.