Nozzle design, droplet size and travel speed can interact to affect the direction that droplets travel after they exit the nozzle. The resulting direction of travel is referred to as the ‘droplet trajectory’.

Higher forward-spraying speeds have a greater impact on the trajectory of large droplets, which tend to hold their direction of travel more readily than smaller droplets. Increased travel speeds increase the horizontal movement of the droplets in the direction of travel. This can increase the deposition of larger droplets onto the leading face of vertical targets, but also onto ‘false’ targets (such as standing stubble) and may leave a 'shadow' behind the vertical target where coverage is reduced.

The angle at which a droplet strikes its target surface can affect retention. Generally, the sharper the angle of impact relative to the surface, the less likely a droplet is to be retained on the target, particularly as the droplet size increases.

Notes

• As with any claim that is made about things that will improve efficacy, look at the evidence provided and consider the source of the data. For example, a herbicide manufacturer that recommends a particular type of nozzle for a specific product will normally have good efficacy data to support that recommendation.

• Generally, nozzles will provide better efficacy at slower spraying speeds or with increased application volumes. Decide how relevant the application parameters used in a trial are, compared to how they will operate in your commercial practice. Especially when it comes to speed and application volume.

Angled nozzles and twin nozzles

Many angled nozzles and nozzles with twin patterns (‘twin nozzles’) have become available in recent years. Forward-facing patterns can be useful for increasing deposition onto vertical targets. Rear-facing patterns can help to overcome the effects of shadowing that may occur with some targets when using large droplets, provided the travel speed does not exceed the speed of the droplets leaving the nozzle. However, DO NOT use rear-facing nozzle patterns with smaller droplets and fast travel speeds (i.e. above about 15-18 km/hr) as this will greatly increase spray drift.