Wind speed is one of three main factors influencing spray drift - the other two are boom height and nozzle design. Guidance on wind speed is given in the Defra Code of Practice for using plant protection products and relates to wind speed at boom height.
| Wind speed at boom height | Guide for using a standard crop sprayer |
||
|---|---|---|---|
| m/s | km/h | miles/h | |
| < 0.6 | < 2 | < 1.2 | Use only medium or coarse spray quality |
| 0.6 - 0.9 | 2 - 3.2 | 1.2 - 2 | Acceptable spraying conditions |
| 0.9 - 1.8 | 3.2 - 6.5 | 2 - 4 | Ideal spraying conditions |
| 1.8 - 2.7 | 6.5 - 9.6 | 4 - 6 | Increased risk of spray drift. Avoid spraying herbicides and take special care with other pesticides |
| > 2.7 | > 9.6 | > 6 | Do not spray |
However, boom height can vary and wind speed at boom height will also depend on the crop height. Met office windspeed data is usually measured at 10 m. Or you might use your own weather station which is positioned at a different height - perhaps 2 - 3 m.
How do you know what the approximate wind speed at boom height would be? Use the calculator below to help decide if conditions are appropriate.
Remember: