Maximising Spray Results in Stubbles

Nozzle Setup: Aiming to get a double overlap occurring with your spray nozzle output.

Should be set up at a 50 cm spacing with a 10 degree fan angle

When stubble is introduced into the system the stubble provides a false floor. This leads to the spray jet overlap occurring within the stubbles canopy. This minimises the degree of contact the chemical has with the weeds. In order for the spray overlap to occur prior to hitting the stubble the height of the stubble must be accounted for when setting your boom height.

Spray Direction: When spraying headlands make sure that you try and travel in the same direction as the stubble. If you spray across the stubble more of the chemical may end up stuck to the stubble instead of penetrating the stubbles canopy and making contact with the weeds below.

boom height

Wes from Nufarm

There are a range of methods that you can apply in order to increase stubble canopy penetration. The first being to increase the droplets size, by having a larger droplet the droplets trajectory is much steeper than the lighter droplets. Within the inter row all droplet sizes have been seen to penetrate although for the weeds that grow within the row a much larger droplet size is needed in order to obtain significant enough herbicide contact.

Pre-emergent: For pre-emergents most growers are using air induction nozzles in order to minimise the velocity of the droplet being released. The air that is inducted within the droplet acts as a cushion during contact that minimises the chance that the droplet will splatter and miss the target. The larger droplets that aren’t air inducted have a much higher velocity and are prone to splashing off the target upon impact.

Wes from Nufarm talking on our field day tour

Water Volume: Where there is very little stubble rates 40-50 litres of water may be used although in a heavy stubble paddock the rate will need to be increased to 60-70 litres of water in order to achieve the same result.

Speed: By slowing down while spraying you have a higher chance of getting the droplet on a more vertical trajectory to the target species. Under a heavy stubble load it is ideal to reduce your speed to 16-18 km per hour.

Weed stresses: In conditions where there is a very dry sub soil with summer storms over the top weed stressing may occur. The weeds use the available moisture to get a good germination and then begin to stress quickly as they use up the moisture within the profile. The key here is to get on top of the weeds as soon as possible before they become too stressed. For summer spraying make sure that you’re using that larger droplet size in order to maximise in longevity on the surface of the weed. Summer grass weeds will tend to stress before broad leaf weeds do.