Spray Drift from Agricultural Pesticide Applications

Abstract

Pesticide application on the Canadian prairies is primarily by tractor drawn groundrig, with some 5–10% carried out by aircraft. Both types of application have been investigated through field trials to determine the amount of sprayed material leaving the target area at the time of application and the amount of volatilized active ingredient drifting off in the subsequent hour or two following spraying. Variations in this initial off-target drift have been related to meteorological conditions (primarily windspeed), to chemical formulations of the pesticide (generally 2,4-D formulations), and to sprayer parameters such as nozzle type, orientation, and hydraulic pressure. Target deposit masses, off-target deposition, and droplet size distributions of the swath deposits and drift fractions were also measured. Finally, the decrease in drifting droplet mass with increasing downwind travel was investigated under various meteorological conditions. Results to date indicate that some 30–40 % of initially deposited butyl ester of 2,4-D evaporates and drifts downwind as vapor in the 2 hr following spraying; the corresponding figure for the octyl ester is 10–15%. Off-target droplet drift at the time of spraying varies between 1 and 8% for ground-rig application, depending on nozzle type and wind-speed, and is some 20–35% with aircraft spraying.