Weather for drone spraying

Spray drones follow the same agronomic rules as ground sprayers — Delta T, humidity, thermal inversion, spray drift and rain all matter in the same way. But a drone adds its own weather limits, related to flight, batteries and satellite positioning.

Rotor downwash

The rotors push air down through the spray, which helps drive droplets into the canopy. The effect depends on the drone, the payload, the flight height and the speed. At higher speed or greater height, the downwash reaches the canopy with less force and the spray is more exposed to crosswind. A crosswind can also bend the downwash so the swath shifts downwind. Follow the manufacturer's recommended height, speed and swath width for the product and crop, and adjust them when the wind picks up.

Flight height and speed

Flying higher than recommended gives droplets more time in the air and more exposure to wind; flying too low over an uneven canopy can cause striping and uneven deposition. Faster flight reduces application time but widens the wake and can reduce canopy penetration. Terrain-following and a correct height above the canopy matter most on slopes and in tall crops.

Maximum wind resistance is not a spraying limit

Manufacturers publish a maximum wind resistance for each drone: the wind in which it can fly and hold its position. That figure is a flight limit, not a spraying limit. A drone that can fly in strong wind will still produce heavy drift in it. For spraying, use the wind speed range the label and good practice allow, which is usually well below the airframe's limit, together with a suitable droplet class.

Wind at altitude

Wind generally increases with height above ground, and gusts can be stronger aloft than at the surface. Forecast wind is usually given at 10 m. Even when the drone sprays a few metres above the crop, climbs, transit flights and returns to the take-off point happen higher up. Check the wind at the heights you will actually fly, and the gusts, before take-off.

Battery temperature

Lithium batteries lose capacity and power in the cold and are stressed by heat, and manufacturers specify an operating temperature range for the drone and its batteries. In hot conditions, batteries fresh from charging or left in the sun may need to cool before use; in the cold, flight time is shorter. Plan the number of batteries and the charging cycle around the day's temperatures.

GNSS, RTK and the Kp index

Spray drones rely on satellite positioning, usually with RTK corrections, to follow straight, evenly spaced passes. Poor satellite geometry or geomagnetic activity can degrade accuracy and cause gaps or overlaps. Check satellite availability and the Kp index before a job — see Kp index, RTK and GNSS.

Rain

Most spray drones are not designed to fly in rain. Rain also washes product off the leaf and makes the application pointless. Stop before rain arrives and allow the product's rainfast period — see rain and spraying.

Regulations

Drone spraying is regulated in most countries, often by both the aviation authority and the agricultural or pesticide authority. See agricultural drone rules by country, and always follow the label for aerial application.

In PulveCast

For drones, PulveCast loads the wind and temperature limits of your drone model automatically and adds the Kp index, visible GNSS satellites and an RTK signal estimate to the agronomic checks; the wind profile by altitude is part of Pro.

More guides

• Delta T for spraying: what it is and why 2 to 8 °C
• Delta T chart: how to read it
• Thermal inversion and spraying
• Spray drift: causes and how to reduce it
• Wind speed for spraying
• The best time of day to spray
• Humidity and dew point for spraying
• Rain and spraying: rainfast periods and forecasts
• Temperature and spraying
• Droplet size and nozzle selection
• Kp index, RTK and GNSS for spray drone operators
• Pre-spray checklist