A guide to estimating wind speed
Use this guide to estimate wind speed to help you plan to safely spray agricultural chemicals.
Calm wind
Wind speed – 0 km
Visible signs – Smoke rises vertically; spreads out under inversion layer. Flags hang limp.
Spray drift risk – High. Unpredictable vapour and mist drift.
Light air
Wind speed – 1-5 km
Visible signs – Smoke drifts slowly. Flags just begin to move.
Spray drift risk – Moderate–low. Inversion conditions could still be present.
Slight breeze
Wind speed – 6-11 km
Visible signs – Wind felt on face; leaves rustle; flags stir from flagpole.
Spray drift risk – Low
Gentle breeze/wind
Wind speed –12-19 km
Visible signs Leaves and small twigs in constant motion; wind extends a light flag.
Spray drift risk – Moderate–high. Need to carefully monitor conditions.
Moderate wind
Wind speed – 20-29 km
Visible signs – Wind raises dust and loose paper; grasses lay over and small branches are moved; flags flap.
Spray drift risk – High. Droplet drift and vapour drift are almost certain.
Fresh wind
Wind speed – 30-39 km
Visible signs – Small trees in leaf begin to sway; crested wavelets form on inland waters, flags ripple.
Spray drift risk – Very High. Unsuitable for spraying.
Strong wind
Wind speed – 40+ km
Visible signs – Large branches move; whistling heard in wires, flags beat.
Spray drift risk – Extreme. Unsuitable for spraying.
Notes
This guide to estimating wind speed is not intended as a substitute for electronic hand held weather meters, which are available from spray equipment suppliers. Wind speed should be measured at spray application height. Some product labels specify a wind speed range for spraying. Check the product label prior to spraying.
Reduce risk from spray drift:
- Ensure wind direction is safe.
- Ensure wind speed is safe.
- Allow adequate downwind buffer zone.
- Lower boom height
- Reduce travel speed.
- Increase droplet size by:
- Increasing nozzle size;
- Changing nozzles;
- Reducing pump pressure.
More resources
- Buffer zones and vegetative barriers — Buffer zones and vegetative barriers are valuable tools that can be used to reduce the potential for spray drift when applying agricultural chemicals.
- Living in harmony pesticides and bees — Information on managing risks associated with agricultural spraying near apiary sites.
- Recognising surface temperature inversions — It is unsafe to spray when conditions favour surface temperature inversions, due to the potential for spray drift. Learn how to identify weather conditions associated with surface temperature inversions.
- Spray drift restraints and mandatory buffer zones — This page explains some of the operating principles in relation to spray drift risk such as how to correctly apply mandatory buffer zone labels.
- Volatile vapour drift risk — Learn about the risks associated with volatile vapour production by ester formulations of phenoxy herbicides.