Spray boom technology - improving coverage and managing drift

Author: | Date: 09 Aug 2017

Take home messages

  • When spraying, be aware of the environmental conditions around you at all times.
  • Read and adhere to the label. There are mandatory instructions on the label for some products.
  • Know when to spray and when not to- is there an inversion?
  • Keep your spray in your paddock.


For a number of years spray drift has been a problem but in the last 12 months it has been particularly bad and has caused a lot of off target damage especially in the wine grape growing areas of SA. Most of this herbicide damage has not been caused by direct drift but by inversion drift. Locally the damage was recorded from one end of the Clare Valley to the other and it needs to stop.

Some of our more commonly used herbicides are under threat; they are coming under more restrictions or at worst are under threat of being removed from the market for a period of time, or altogether - a practice that is now happening overseas. Not only are the Clare Valley viticultural areas being affected, but also neighbouring properties and communities, a point that is often over looked.


It’s important that you make sure you know the capability of your boom sprayer. What is the pump capacity, can you increase water rate if you need to, especially in the summer months when evaporation is higher, or do you just have to slow down?

What does the label say about droplet size? More and more labels are asking for course to very course droplets when spraying so it is important that you check your nozzle chart. Most likely you will need some form of air induction nozzle to comply with the label requirements.

Check the weather at the application site. You should measure temperature, humidity (Delta T) and wind speed. Unfortunately, many growers and advisers think that when there is no wind it is a good time to spray but in reality it is one of the worst times, as you have no idea where the spray will go or end up.

Check whether there is an inversion –do know how to recognise one? In general, there is an inversion most nights, normally occurring one and a half hours before sunset and continuing until one and a half hours after sunrise. In general, inversions don’t occur  if it is overcast, wind blowing over 11kph, or when it is raining. As stated on most crop protection product labels, spraying is not permitted when an inversion exists.

Boom height

When operating a boom with 50cm nozzle spacing, boom height with 110 degree nozzles should be 50cm above the target area. If your boom is higher than 50cm there is a greater reliance on gravity compared with hydraulic pressure to get spray to the target area, which in turn increases the chance of drift.


Although many spray units are capable of travelling at speeds in excess of 18kph it is recommended that spraying is not undertaken above this speed, unless  the boom can be kept stable at a height of 50cm above the target.


Growers need to adhere to crop protection product label requirements for application conditions and learn to recognise when inversion occur to determine when not to spray and when it’s safe to spray.

Agriculture is our industry and we want to keep it without further regulation. It’s up to us to all work together and to get it right so that further regulations are not required.


The GRDC has a number of resources available to assist growers including:


The author would like to acknowledge Bill Gordon and Graeme Tepper for the use of some of their data and slides and also thank GRDC and ORM for the opportunity to speak to you today.

Contact details

Peter Cousins
PO Box 31
Crystal Brook
0408 210 893