Inversion and drift: Risk factors

June 20, 2018 – Issue 12

Risk factors for wind-blown herbicide drift: Fine spray droplets and higher winds can cause sprays to drift to off-target areas. Drift tends to affect only those plants immediately downwind, but it can move several feet into shelterbelts and neighbouring fields. Drift prevention tips.

Drift into a bush

Spray drift from a canola field can be deadly to neighbouring crops.

Risk factors for inversion-caused herbicide drift: Low wind and clear skies can cause inversions, where air is cooler and heavier at ground level. (How to identify an inversion scenario) Clouds of spray hang in the air and, over the course of an evening, can slowly move over the landscape causing damage to susceptible plants along the way. Inversion spray clouds are potentially worse than drift because they can travel many kilometres. Coarse spray droplets do not tend to hang up in an inversion, but fine droplets will, and even a coarse nozzle will produce some fine droplets. Herbicides that form vapour (gaseous forms of the chemical) will also move in an inversion and these vapour clouds can be especially damaging. Dicamba will form vapour clouds. Sprayers 101 on vapour drift and inversions

The cloud behind the sprayer is a sign of inversion, and higher drift risk. Source: Tom Wolf

Further reading:

@Spray_Guy tweet on relationship between boom height and drift
Canola Watch quiz – spraying
Canola Watch podcast on inversions
NDSU Extension Service factsheet: Air Temperature Inversions

Canola Watch