Understanding Herbicides Through Controlled Trials

Dr Peter Boutsalis talks about herbicide trials happening at the University of Adelaide.

Since 2005 the GRDC has been funding us to do these trials and we’ve sort of moved right across the South Australian and Victorian cropping zone. We’ve got a lot of ideas we want to test, and we do test them in pots firstly just to get an indication where we need to go in the field.

A lot of our work is always done with a standard potting soil, which is good for just testing differences between a variety between resistance, but for real life information it’s not so we’ve actually gone and go regularly and obtained soil from the paddock – different paddocks with different soil types.

We can use these soil types in pots to get a really good indication as to how herbicides are behaving in the system, so we can use traditional pots with different types of soil and vary our crop seed according to whatever depth we’re looking at. Also we can impose different rainfall we can decide when it rains.

Herbicides and Stubble

We’ve definitely noticed that some herbicides are very much affected by the stubble, such as trifluralin. We know that if trifluralin contacts stubble, it can bind very strongly and therefore you don’t get very good weed control. We use herbicides such as Secura. There are indications are that it washes off stubble and therefore this herbicide even if you’ve got a thick stubble load, it will wash off quite well if you’ve got good rainfall soon after spraying.

One of the important pieces of equipment that we have is a laboratory sprayer where we can control the nozzles, the water volume, the speed to some extent, so really create better conditions. different herbicides and different rates and different heights according to what’s required. Here in this trial we’ve got up to 50 odd different herbicides, individual herbicides and herbicide combinations to try and get indications of which ones may be really effective in the field.

We’ve sown a wheat variety and also a t-resistant rye grass and two different brome species. So from over on the far area here we see we have none sprayed and the back row has lots of raw grass and other weeds. These are single herbicides that we use. Then as we move more and more we snake along ride up to where I am, we start using two herbicide combinations and even moving towards here we start by using three herbicide combinations.

Trialling Combinations of Active Herbicide Ingredients

So what you can see is that as you increase the different amounts of active ingredient or the combination of active ingredients We are starting to get better and better control but, you know, we can bring the paddock right here, control all the variables so we can start separating out so the most important variables for each of the the herbicides.

We can control all of the environmental factors here so we can start to get an indications of how these herbicides work.