What’s the point of harvest weed seed control?
Reducing the seed bank, right!
Yes.
And.
Stopping the spread of weed patches.
This second point is often overlooked, and it may even be just as significant as the seedbank that we have all been focused on for so long.
Don’t get me wrong, I’m still a big advocate for low seedbank farming, but maybe its not the only reason to use harvest weed seed control.
I’ve just read an old research paper by Canadian Steve Shirtliffe. He researched wild oat seed spread in the late 90’s comparing a harvester fitted with a chaff cart to one without a chaff cart.
He found a big reduction in wild oat seed spread where the chaff cart was fitted.
For the combine with a chaff cart, there were fewer than 10 wild oat seeds/m2 spread at 45m from a weedy patch.
Without the chaff cart, there were more than 10 wild oat seeds/m2 spread up to 145m from the weedy patch.
Before you get your knickers in a knot about wild oats shedding their seed, you need to understand that for this research, they windrowed the wheat crop early at 35% moisture, and there was a lot of wild oat seeds retained on the seed head at this point.
We also need to understand that the wild oat seeds were mostly found in the chaff fraction at harvest, making the chaff cart very effective at minimising seed spread. Fortunately, this is also the case for many of our weeds that we are targeting in Australia.
It makes perfect sense, doesn’t it? A harvester travelling through a weed patch is going to spread the weed seeds. I don’t think that will surprise anyone.
What does it mean for our weeds?
If we think about it, we know that herbicide resistance starts in an individual plant with a random mutation, the plant sets seed, and a weed patch begins.
If we then harvest through this weed patch, we can spread it over a big area in just a couple of years.
We do it all of the time with glyphosate resistant ryegrass on our fencelines and firebreaks by putting the header comb close to the fence and dragging the resistant plants into the paddock.
And if we are using harvest weed seed control, and the weed seeds are in the chaff fraction, we can significantly reduce this spread.
Then what can we do?
I think using HWSC can buy us some time to work out what to do with these patches of resistant weeds.
If we have spread the weeds all over the paddock, and then discovered the resistance, we are buggered.
But if we can keep the resistant weeds to their patches for a couple of years, we can work out a strategy to hammer these patches and adjust our management on the whole paddock before we have a blowout.
And it’s not just resistant weeds that are in patches. There all sorts of reasons for weed patches – soil type, spray misses, trees, rock heaps etc.
Shedding weeds
The other significant factor is weeds that shed their seed, such as wild oats, or, heaven forbid, ryegrass that has evolved to shed its seed before harvest.
If these weeds are left alone for long enough, they will shed their seed before harvest and remain as a patch of weeds.
But what commonly happens is they are halfway through shedding their seeds, then a harvester barrels through them and spreads them from arsehole to breakfast.
Then we have early shedding weeds spread nicely all over the place.
Noice one Gary!
Patch management
As I’ve previously written, we are on the cusp of having plenty of technology that is going to help us add extra management to patches of weeds. Cameras, drones, AI, satelites etc. etc.
Lets keep the weeds in patches, then we can deal with them there with some smart tech in the future.
The Terminator Agronomist
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P.s. Ask the terminator a question by return email, and get a blunt answer next month.
P.p.s. Please note this advice is general in nature and not based on your specific circumstances.