Time to re-think weed plan
Resistance to glyphosate a growing problem that needs fresh thinking
THE weather is not good for using herbicide for weed control is it?
The weather is not even good for germinating weed seeds over this summer, so when they do germinate after the next significant fall of rain, there will be thousands of them and they will be a mixture most likely of summer and autumn weeds germinating all over the place.
Also many of them may have a real percentage of herbicide resistant species in amongst them.
In our fallows then without doubt, the main herbicide used is glyphosate, plus you may add other herbicides to give you better control across your weed spectrum.
Nothing wrong with this plan as we have doing it for over 30 years.
Maybe that is a cause for concern the 30 year long period of minimum or zero till practices, we have all engaged.
Just because we only used 1L per ha of Roundup 450 CT in 1985 on elongated milk thistle plants for effective control, as it was fairly expensive at $23/L and then herbicide costs were a real concern.
These days we still have elongated milk thistle in our paddocks and how much glyphosate do we apply these days?
I would hazard a guess we are closer to 2–2.5L per ha for effective control with a much cheaper glyphosate 450 at $4 per litre.
So what would this tell us with respect to milk thistle over the last 30 odd years about getting harder to control?
Something is going on if we were killing milkies in 1985 with 1L per ha and now we are needing to apply 2–2.5L per ha.
Surely that may tell us about this rate creep or maybe we should say rate gallop of our brilliant fallow herbicide in glyphosate.
That word resistance gets bandied about a fair bit these days doesn’t it?
Herbicide resistance is the inherited ability of a plant to survive and produce seed, from a previously normal lethal rate of herbicide.
So if we were using 1L per ha of glyphosate in 1985 and now are using automatically 2L per ha or above, that would suggest to me that we have a rate creep and indicates that we have controlled successfully all the least resistant plants of milk thistle and now we are coming up against the more difficult ones.
Sure, we have all observed the weeds in the paddock that are made sick from a herbicide application and they recover to set and drop seed, however we have always assumed it was poor coverage, bad environmental conditions, a more stressed milkie from mechanical damage of wheels or dust and the list goes on.
Our definition of herbicide resistance is the acquired ability of a weed population to survive a herbicide application that used to control it.
Population is an important word in this definition of my shortened explanation of resistance.
Herbicide tolerance is used around our crop safety aspects and an example would be the old Dicamba broadleaf product registered for over the top spraying of many grass crops.
Dicamba has some good aspects on weed control, however crop safety on some older barley varieties was not one of them and as I recall my father, Alec, many years ago denouncing Dicamba to all and sundry that it “wrecked” one of our sown barley varieties’ yield by about 70%.
Then you have the other side of weed control, where I have been recommending for many years, glyphosate plus a companion product for buckwheat control.
Glyphosate on its own has never been good on buckwheat or wireweed and only claims suppression on labels.
So where does all this wordage leave us.
It leaves us wondering how long am I going to be able to use a vital product like glyphosate and other herbicide actives in my weed control handbook, unless I
change my ways.
It may not be next week or even next year for the glyphosate product to run out of usefulness in your paddocks.
However it is coming, unless you diversify your weed control methods.
So you and your agri adviser need to run some “what if” plans, and feel free to call your neighbours in as well.
If you get enough takers feel free to give me a call also.
GROWING ISSUE: Prickly lettuce is an increasing problem.