December 6, 2024
Written by: Peter Newman
If you get better at endurance running, chances are you’ll get a bit worse at sprinting. Roberto Busi has won marathons, but I’m pretty sure I’ve got him covered over 50m.
And if you get good at lying on the couch, you’ll probably get worse at any form of running!
AHRI researchers Danica Goggin and Roberto Busi have now found that if you get prosulfocarb (e.g Boxer Gold/Arcade) resistance, your trifluralin resistance might go away.
And did you know that prosulfocarb isn’t even a herbicide? Well, that’s kind of true! It becomes a herbicide inside the plant after it is converted into prosulfocarb sulfoxide by an enzyme. This is what is known as a pro herbicide.
This AHRI Insight looks at cross resistance between some of our main pre-emergent herbicides, understanding the mechanisms, which helps us give advice on how to mix and rotate between these products.
There’s also a lesson about which herbicides are more active in the roots v shoots, and how this affects application.
A few years back I was looking at some trial pots at the UWA glasshouses area with Roberto Busi and Steve Powles. Roberto showed us where he started with some nasty, resistant ryegrass, and using recurrent selection, he ‘bred’ prosulfocarb (e.g. Boxer Gold) and pyroxasulfone (e.g Sakura) resistance.
The super interesting thing was that as the prosulfocarb resistance increased, the trifluralin resistance disappeared.
At first, we thought that this was just genetic drift that comes along in glasshouse studies from time to time. But further research confirmed that this was actually negative cross-resistance at play.
Negative cross resistance is where, as you get resistance to one herbicide, you see increased susceptibility to another herbicide. And it’s very rare. Another good example is bromoxynil and Atrazine – but that’s another story.
Roberto also found cross resistance between Boxer Gold and Sakura. That is, as he selected for resistance with just one of these herbicides, he saw resistance evolve to the other, even though it had never seen this herbicide.
This prompted Danica Goggin and Gregory Cawthray to team up with Roberto to try and work out what was going on. Here’s a summary.
Roots or Shoots?
Prosulfocarb is more active in the shoots (coleoptiles). Agronomists have been onto this for a long time, and often target using this herbicide after rain but before emergence for this reason. It also explains why prosulfocarb has some post-emergent activity.
Thanks to this recent research, we now know this is because the roots aren’t very good at activating prosulfocarb, while shoots are super-efficient at turning prosulfocarb into its herbicidally active sulfoxide form.
Trifluralin is pretty good at inhibiting both root and shoot growth, but the shoots are better at breaking down the herbicide. If there’s metabolic resistance to trifluralin, it’s mostly happening in the shoots.
Negative cross-resistance
We know that this is real, but we don’t really know how it’s working.
We also know that it works in one direction, but not sure about the other direction. That is, if you start with trifluralin resistant ryegrass, and recurrently select it with prosulfocarb, the trifluralin resistance can disappear. But we don’t know if you start with prosulfocarb resistance, can we make it go away?
We also know that this phenomenon only works for metabolic trifluralin resistance. If the trifluralin resistance is due to a target site, this won’t work.
And, we know that in most populations, we are likely to have both target site and metabolic resistance.
Cross-resistance between Sakura and Boxer Gold
We know that in the glasshouse, we can select for resistance to either one of these herbicides, and we end up with resistance to the other one. This is cross resistance.
We also know that the main mechanism of Sakura (pyroxasulfone) resistance is due to GST’s.
And, due to this research, we now also know that the cross resistance between Boxer Gold and Sakura is not due to GST’s.
Confusing hey!
What does this all mean? It means there could be another Sakura resistance mechanism that we haven’t worked out yet. We have a few hints that P450’s could be involved, but more research is needed.
Two main messages
There are two main messages that come out of this research.
- Avoid rotating between Sakura (pyroxasulfone) and Boxer Gold/Arcade (prosulfocarb) type products. We know that there is cross resistance between these two herbicides, so while they are different chemicals, the plant may see them as the same chemical in terms of resistance.
- Keep mixing and rotating between trifluralin and Boxer Gold/Arcade (prosulfocarb).
Trifluralin is the obvious mixing partner for many pre-emergent herbicides. If we can give it a rest in some years, then yes, we should do that. But, on the other hand, there’s a lot of good reasons to keep it in the mix from both efficacy and resistance points of view. If trifluralin is still working, keep it in the mix.
Conclusion
This is where all of this detailed work on herbicide resistance mechanisms pays off. These researchers write papers that are nearly impossible for mere mortals like me to read, because the science is so complex. But at the end of the day, they can distil it down to some very simple messages that will help farmers the world over.
Mix and rotate!
Paper
Posted in: AHRI Insight, Herbicide resistance mechanisms