Australian Herbicide Resistance Initiative (AHRI) insight #149 - 2,4-D antagonises glyphosate, especially in glyphosate resistant weeds
Australia
November 2020
Written by Peter Newman
Back in the day we used to open a drum of herbicide in the corner of the paddock and the weeds started dying. Some weeds were so susceptible that we could just put a drum of herbicide on the back of the ute and drive around the farm and the weeds would turn up their toes because they knew what was coming!
OK, this is a mild exaggeration, but generally speaking the weeds were so susceptible that we could get away with a sub-optimal spray job, and the weeds would die.
Now that we have resistant weeds, we really need to hold our tongue right when we’re spraying to give us any chance of success.
We have known for some time that when mixing 2,4-D with glyphosate there can be some antagonism and grass control can be compromised. However, the antagonism is often relatively minor and can often be overcome by selecting the right formulation with perhaps a minor rate adjustment.
Some recent research by a former AHRI researcher Jingbo Li and others shows that glyphosate resistance changes this. They studied two populations of barnyard grass with relatively low-level glyphosate resistance and found that when 2,4-D Amine or Ester was added to the tank with glyphosate, barnyard grass control was greatly reduced. They went on to discover that this is due to an effect on uptake and translocation.
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