Glyphosate cannot be lost
US farmers having big trouble with resistance
APOLOGIES for talking about weeds again when it is so very dry in all areas of Queensland.
I believe it will break eventually and as we get closer to summertime, then our summer storms could well be large and rapid.
These storms, with some significant rain in them, will bring up a heap of weeds and in days gone by we would rush out about seven to 10 days after the rain has stopped and apply a robust rate of glyphosate with possibly a companion product, if future crop selection allows it with plant backs.
We all know that glyphosate forms the backbone of our spraying programs in trait crops and fallows, so while losing a group A fop or dim would make it fairly difficult for grass control in broadleaf crops, we could probably live with it. We really cannot afford to lose glyphosate.
That comes from one of my bosses, Professor Steve Powles from AHRI in Perth, and I really do agree with him.
As much as I can conclude, there are maybe six mechanisms of glyphosate resistance in Australia now.
The one mechanism I wish to comment on is gene amplification.
If you are still recovering from my statement of six mechanisms of glyphosate resistance in Australia, you can breathe a little easier knowing they are not all present in Queensland... yet.
Right, the gene amplification resistance story.
Glyphosate controls plants by inhibiting a critical plant growth enzyme called EPSPS.
So for years we have been using label rates of 500ml to 3L/ha of glyphosate and these millions of molecules of our favourite knockdown herbicide penetrate the leaf surface and make their way to the plant growth enzyme called EPSPS to halt further growth and the plant dies.
A good result and explains a lot from over the years of using too low a rate at times and getting a poor result.
Many of us have heard the Yanks are having massive problems with palmer amaranth, which is evolved to glyphosate-resistant status.
After many years of spraying glyphosate in fallow and over cotton, corn, soybean crops etc, this tall amaranthus species in the US has become glyphosate-resistant due to this newish mechanism of gene amplification.
So all the easier-killed plant lines of palmer amaranth have been taken out through the years and now, through lack of diversity in herbicides, the surviving amaranth weeds that are left have a peculiarity of being able to produce massive numbers of EPSPS enzymes that basically soak up the glyphosate.
With the glyphosate molecules soaked up into a molecular sponge, the remaining plant EPSPS enzymes carry on inside the weed to allow its normal metabolic functions to continue through to seed set.
This is not a new, mindbending occurrence, as insects like aphids have done this as well elsewhere and we sure have had some practise controlling various resistant insects through the years.
What is not good is that this type of resistance is heritable, meaning it is maintained and apparent in future seeding generations.
Now, this gene amplification “uniqueness” is present in annual ryegrass.
The years-ago-planted livestock feed solution is now a number one herbicideresistant plant in our southern farming system.
The GA presence isn’t as high as palmer amaranth, however these credible research findings should teach us all that weeds have abilities to resist our human attempts to control them.
HOLDING OUT: Queensland amaranthus is yet to become herbicide-resistant in Australia, unlike its American counterpart, palmer amaranthus.