Weeds just waiting for rain
Dry weather means no weeds... for now
WITH the current run of dry weather we really do not have too many weed issues.
We are not even receiving those annoying 5-6mm falls of rain that do very little for soil moisture levels and invariably just bring up a few grass and broadleaf weeds.
So why would I be talking about weeds this week?
It is surprising how quickly the whole situation can turn around in the rainfall department and therefore weed germination and emergence.
Many of us have observed this before with an extended dry time, when along comes some significant rain and you then get eight months of weeds emerging over the next couple of weeks.
So your impeccably clean fallow blocks can get very dirty, very quickly.
In the last 15 years or so gone by, we would grab some glyphosate herbicide and load up the spray rig with 2L or more per ha of this brilliant knockdown product to regain control of our paddocks.
No need for any other mixing product as it was cheaper to use more and more glyphosate per hectare and I was as guilty as anyone of overusing in these cheap glyphosate herbicide years.
Originally in the early 1980s with the price of $23 per litre equivalent for Roundup CT, we had to mix compatible herbicides to keep the cost per hectare down, especially for broadleaf weeds, which unwittingly gave us different modes of action in the tank.
The price per litre for gly dropped down to around $15 per litre in the mid 1990s and still we mixed and matched herbicides to bring down the cost to the farmer. Not that we really worried too much about modes of action, it was more the cost per hectare we were all concerned with.
So then the glyphosate-only bandwagon had really kicked in by the early 2000s and that
❝Remember we need to stop seed set at all costs.”
— Paul McIntosh
is when we really started to select for herbicide resistance.
You have all seen research figures of herbicide resistance levels climb steeply after five or 10 application events or shots.
That has always intrigued me for validity, as one thing experience can do was to make you more cynical on herbicide resistance occurring at all.
How wrong I was.
So where does the phrase “rotating buys you time, mixing buys you shots” come from and how does it apply to us?
Is this how we have held off resistance weed increases, until this decade in some species, because we were mixing compatible herbicides together at full rates?
Overseas research and here in Australia also has
stated and graphed out that having 2.5 modes of action in each and every application on weed cohorts per year, can make you 83 times less likely to develop glyphosate resistance.
So mixing effective herbicide partners as we have done and are continuing to do is very important.
By effective, I mean it is a waste of time if your paddock has a very high level of resistance and you continue to apply this tank mix , which may leave only one product doing the work.
More next week on rotation and mixing of our herbicides.
Remember we need to stop seed set at all costs to take back our paddocks from worsening weed issues.
Weed resistance levels in a paddock should not control our future economic cropping decisions.