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How far does herbicide drift when it’s sprayed from the air?

Category: Herbicide Operations

All jurisdictions in Canada specify the acceptable weather conditions in which aerial applications can be completed. Applicators are well trained to consider factors such as wind speed and direction, spray release height, temperature and humidity that can influence the potential for off-target drift. Modeling studies demonstrate that under common use scenarios drift is unlikely to exceed 2% of the application rate at distances greater than 25 m downwind

Aerial distribution systems for herbicide applications are designed and calibrated to produce large droplets. Large droplets deposit either directly beneath or immediately adjacent to the aircraft path.

For example Thompson et. al. (2012) used a modelling exercise to plot deposit from aircraft as commonly equipped for applications in three Provinces (Alberta, New Brunswick, and Ontario). The model predicted very minor fractional amounts of downwind deposit in all scenarios with deposit beyond 25m, never exceeding 2% of the application rate.

Applicators are trained to be constantly aware of environmental factors (wind, temperature, etc.) that influence drift and to observe label and regulatory requirements designed to minimize off-target drift.

Thompson D, Leach J, Noel M, Odsen S, Mihajlovich M. Aerial forest herbicide application: Comparative assessment of risk mitigation strategies in Canada. The Forestry Chronicle. 2012; 88(2):176-84.