MANY years ago, I really did believe that those of us in the northern area with summer and winter cropping rotations would be impervious to developing herbicide resistance.
Fast forward to present day Queensland and we are looking seriously at weeds like Barnyard grass, Fleabane, Feather Top Rhodes and Urachloa developing this fast spreading glyphosate resistance factor.
In other words you can spray these plants with glyphosate and many will not die and will set viable seed.
So the double knock usage of herbicides was utilised, which describes the technique of using two different modes of action products to control or eliminate our problem weeds in fairly quick succession.
So we initially used glyphosate and a few days later, we then applied Paraquat with some pretty fair results across a range of plants, which protected our zero or minimum tillage operations. For a variety of reasons we needed to protect our zero or min till techniques and they still apply today, however by far the biggest is still our stubble retention with resultant rainfall infiltration and soil moisture storage capabilities.
Well the unlikely has happened in Western Australia, where a vineyard using random method of herbicide selection over many years with both glyphosate and Paraquat has now developed a population of plants that is resistance to both products. Yes, the same plants now have resistance to both these two widely differing herbicides.
I never even considered the aptly bannered Dangerous Poison product of Paraquat being a herbicide that could develop resistance, due to its peculiar mode of action.
So the latest news I have heard is that experts in WA do not know the specific mechanism that causes the link between glyphosate and Paraquat resistance.
Speculation is revolving around the reduced translocation of each product, but the connection between these two mechanisms is independent. So under ideal selection conditions for multiple resistance, this ryegrass population now has this major resistance issue.
We cannot just toss double knock out the window due to the many benefits it provides, however we are provided with a timely warning that if we get careless with our rotational crops and herbicides, we will be looking down the barrel of being unable to grow certain crops due to weed pressure.
No matter what products and strategies you use, there is an absolute critical need to have no survivors left in your paddock for them to set seed.