Wind, sun, humidity — choosing the time to spray so the product is not wasted

Spray the right product at the right rate but at the wrong time, and you can waste it across the whole field.

Wind

The most important variable. Strong wind makes droplets drift off target, which wastes money and may affect neighbouring fields, especially fields growing different crops or organic fields.

Completely still air is not always the best condition either. In very still air combined with cool air near the ground, small droplets may hang in the air and then move a long way in an unpredictable direction. A light, steady wind with a known direction is usually easier to manage.

Sun and temperature

Very hot weather makes droplets evaporate before reaching the leaves, especially small droplets, and crops under heat stress are more likely to suffer leaf burn from the product. Early morning and evening are therefore the times commonly used.

Relative humidity

Low humidity speeds up droplet evaporation. High humidity helps droplets last longer, but if the leaves are already very wet, the product may run off the leaves instead of staying on them.

Rain

Rain after spraying is the most obvious risk. Each product needs a different amount of time before it is rainfast; this information is on the label. Always check the weather forecast before deciding, and if you are not sure, postponing is usually cheaper than spraying again.

Dew

Heavy dew on leaves affects how well the product sticks. In some cases it helps it spread, in others it makes it run off, depending on the product. Check the specific advice for that product.

Ways of working that reduce risk

Check the forecast in advance and plan over a window of days, not a single day. Have a backup plan for which field to move to if the wind is strong, and decide on site based on actual conditions, not only on the schedule you set.

Our website shows weather information for your recorded fields to help you decide, but the final decision should rest with the person standing in the field. Important note This article explains general principles. It is not a recommendation for any specific chemical. Suitable mixing rates and timing differ by substance, crop, growth stage and field conditions. Always treat the product label as the authority, and ask our staff or an agricultural specialist before deciding.