Getting on top of weeds
BACK onto weeds this week and looking at fence lines and even council roadsides, where the easiest course of vegetation control is to use a heavy spot spray rate of knockdown herbicide, with one part of glyphosate to 100 parts of water being common.
That equates to roughly 10L/ha.
It is cheap, not the worst option in drift or sensitive plant situations, relatively safe to the operator and fairly effective at keeping unwanted vegetation under control for situations of electric fences, paddock boundaries, roadside signage and culvert edges.
Except when herbicide resistance comes along and the hard-to-kill species just grow right through these previously successful herbicide applications.
We often observe a plethora of weeds in the cultivation paddocks when the planter fails to drop crop seed and we have a bare spot of maybe 2sq m or 2ha, that has no useful crop growing on it.
Despite some of our best efforts in using selective herbicides as the sole weed control agent, that very reduced crop density still gets more weeds than you can poke a stick at.
So my point is that crop or desirable plant competition is a great way to reduce our weed count.
So are our roadsides and property fence lines trying to be too clean?
The bare earth principle. What I am suggesting, or should I say challenging everybody with, is to achieve some non-herbicide weed control by encouraging desirable plants to grow as competitors for weeds.
For example, many years ago I saw some straggly buffel grass, over a period of many months, out-perform and therefore outgrow some galvanised burr clumps.
Now buffel is a strong competitor, however so is galvanised burr in overgrazed situations.
The patch of about 1000sq m went from a galvanised burr patch to a standout patch of buffel grass. All the buffel needed was some encouragement and that was done by a simple method of removing all livestock and local roos by a temporary fence erection.
My current thought project is to find ways to leave established pioneer or commercial rhodes grass growing and prevent feathertop rhodes from proliferating along fences and roadsides. Too often I have observed that the pioneer rhodes is killed by heavy glyphosate spraying and the feathertop rhodes then becomes rampant.
It struck me that we all need to figure out our own ways to introduce some desirable plant competition to those pesky weed sites.
My recent trip to CQ certainly saw plenty of parthenium weed out-competing both buffel and leucaena plants, after Cyclone Debbie’s powerful rain event.
Apart from not overgrazing in drought, an unrealistic call, what else could you do for parthenium control in buffel-only pastures?
Well in this case I would use some very economical and selective herbicide in metsulfuron methyl that would clean up the parthenium and leave the established buffel well enough alone.
This herbicide, originally called Ally, would kill or severely suppress any legume plants present at time of spraying by the way.
This Group B mode of action product could be mixed with many other selective options depending on weed spectrum identified and pasture species present.
So it needs some thought for a herbicide package here.
So here I am talking non-herbicide methods at the top and resorting to a liberal rate of metsulfuron methyl at the bottom of the article.
I am merely pointing out that we may need a combination of ideas for the weed control we want.
We need to implement both cultural and chemical controls without losing our precious top soil down the creek.
This would therefore prolong the useful life of our current herbicide packages.
I have not heard of any weed species that can totally resist other desirable plants’ competitive nature, however I certainly know many plant species that can resist herbicides we are currently overusing.
Herbicide resistance is a common phrase these days and it does not have to be a life sentence. We just need to challenge ourselves to obtain weed control by other means.
SPARSE COMPETITION: Agronomist Paul McIntosh checks weed numbers in a patchy grain sorghum crop last summer.