Spray drift happens when wind carries fine herbicide droplets away from the intended target, and the safe application window is generally between 3-15 km/h — below that, temperature inversions can trap droplets near the ground; above it, drift risk to neighboring plants rises sharply.
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Why "No Wind" Isn't Actually Ideal Either
It sounds counterintuitive, but completely still air, especially in early morning or evening, can indicate a temperature inversion — a layer of cool air trapped near the ground under warmer air above. Fine spray droplets can hang suspended in this layer rather than settling, then move unpredictably once the inversion breaks, sometimes drifting significant distances.
The Practical Wind Speed Guide
Wind Speed Condition Recommendation
Below 3 km/h Risk of temperature inversion Use caution; check for inversion signs before spraying
3-15 km/h Generally the safest working range Good conditions for standard application
Above 15 km/h High drift risk Postpone application
Pro tip: A simple field check for wind direction and rough speed: watch smoke, dust, or how leaves move on nearby trees. If leaves are rustling steadily and small branches are moving, you're likely already above the safe spraying range, regardless of what a forecast app says for your general area.
Other Factors That Worsen Drift Beyond Wind Alone
Nozzle type and droplet size: finer droplets drift further than coarser ones at the same wind speed
Spray height: spraying from unnecessarily high above the target increases the distance droplets can travel before landing
Boom or nozzle pressure: excessive pressure produces finer droplets more prone to drift
What to Do If You Suspect Drift Occurred
Check neighboring plants for symptoms over the following days — unexpected leaf curling, discoloration, or stunted growth on plants you didn't intend to treat can indicate drift exposure. Document what you observe and when, since this helps identify whether drift genuinely occurred and from which application.
Watch out: Drift risk isn't just about your neighbor's garden — it's a real concern near your own desired plants, especially when using a non-selective product like our Ammonium Glyphosate 15% near a vegetable bed or ornamental border. Use a shielded sprayer or spot-treatment approach when working close to plants you want to keep.
Frequently Asked Questions
What is the safest wind speed for spraying herbicide?
Generally 3-15 km/h is considered the safest working range, avoiding both the drift risk of higher winds and the temperature inversion risk of completely still conditions.
Can herbicide drift damage plants I didn't spray?
Yes, wind-carried droplets can land on and affect neighboring desired plants, sometimes showing symptoms like leaf curling or discoloration in the days following application.
Why is completely calm weather sometimes risky for spraying?
Very still conditions, especially near dawn or dusk, can indicate a temperature inversion that traps fine spray droplets near the ground rather than letting them settle normally.
Browse our full herbicide range, all formulated for reliable results within standard application windows.
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