Optimisation of spraying technique has many benefits
You have to choose the right spraying technique to get the best biological effect of the treatment and to minimise losses of pesticides to the environment.
When the farmer treats his crops with pesticides it is to protect the crops from weeds, pests and diseases. The sprays are of no use if they do not hit the target and may even be harmful if they end up elsewhere. Therefore it is important that the farmer chooses the right spraying technique.
Identification of the best spraying techniques is something that senior researcher Peter Kryger Jensen from the Department of Agroecology at Aarhus University will be covering in his presentation at the 2015 Plant Congress to be held in Herning in January.
- When pesticides are sprayed on crops losses occur in the form of drift. This is the proportion of the liquid that moves outside the area intended for spraying. Spray drift can occur in two ways – either as deposition drift or as airborne drift, explains Peter Kryger Jensen.
Deposition drift occurs when large droplets of spray are deposited on the ground downwind from the sprayed area. This type of drift can cause damage to neighbouring areas and is the reason why there are regulations in place in crop spraying for a distance buffer to other crops.
The second kind of drift is airborne drift. This consists of very small droplets and because they are so small they drift with the movement of air and are often not deposited on the ground.
The dividing line between the two types of drift is fuzzy since it depends on how far from the sprayed area the airborne drift is measured.
- The two types of drift are supposed to be closely correlated. This means that measures that reduce deposition drift will also reduce airborne drift, says Peter Kryger Jensen.
Spraying under favourable weather conditions with moderate temperatures and a high relative humidity are two useful initiatives. Drift can also be reduced by driving at moderate speeds of up to 6 km/hour, setting a correct boom height of max 40 cm, and using a coarse atomizer in the form of, for example, compact air injection nozzles.
- Experiments in recent years have shown that it is possible to use a coarser atomizer for several crop protection tasks than previously recommended. In principle, the coarsest setting that ensures the best effect of the applied pesticide should be used, recommends Peter Kryger Jensen.