The days of crop topping with glyphosate are numbered.
We have a lot of glyphosate resistance. Lots and lots.
Resistance testing services are finding that about half of the populations tested are resistant to glyphosate.
Half!
50%!
Every second sample!!
These results are higher than the random surveys because they are from samples where farmers and agros are testing where a problem is suspected.
But, regardless of the random vs. targeted survey argument, it’s pretty clear that glyphosate resistance is a runaway train.
We use a lot of glyphosate for crop topping in feed barley and canola, in an attempt to stop ryegrass from setting seed, and you’d be crazy not to if you were faced with ryegrass that is flowering to early dough stage in a mature barley crop.
But pretty soon, this practice is going to be about as effective as spraying the crop with water.
How do you know if it’s working?
Given that the crop and weeds are in the process of dying from terminal drought (haying off) when we are spraying, it can be pretty tricky to see if your crop topping spray of glyphosate has worked?
I’m going to suggest that looking at the crop and the weeds isn’t going to tell us much.
I also wouldn’t recommend trying to do your own germination test. Ryegrass seed is dormant for six months or so straight off the plant. Researchers have tricky ways of breaking dormancy in the lab, but I don’t think you’ll be able to do that at home. You’ve got enough to do anyway.
Sending your seed off for resistance testing is another option.
But
The testing services are going to germinate your ryegrass seed then spray the plants.
If your seeds germinate, this will be the resistant ones. The susceptible ones will not germinate because the crop topping worked on them.
So yes, resistance testing will show you that there is a problem, but you won’t know what percentage of your population is resistant because only the resistant ones will germinate.
Does that make sense?
By all means resistance test your paddocks that you crop topped with glyphosate, but expect your results to be binary. You’ll either get high levels of resistance to glyphosate, or you’ll get a message back to say sorry, we couldn’t germinate your ryegrass seed.
Having said all of that, I would definitely resistance test paddocks that you have crop topped with glyphosate. If you have a big problem, you want to know about it. You could try asking your resistance testing service for your germination results as well. Fill in this form to enter your details for Seed Terminators Sponsored Resistance Program with Plant Science Consulting.
Then what?
Righto, where are we?
You’ve crop topped your barley or canola with glyphosate, you’ve sent a sample off for resistance testing, and it has come back with 100% survivors to glyphosate.
We now know that you have a knockdown problem in front of the next crop.
At the moment you can pivot to a double paraquat knockdown in combination with some pre-em herbicides and other mixing partners.
This will work in the short term, but about now you’re hearing a voice inside your head saying, “this ain’t gonna last."
We also have a halving of the paraquat rate (as a single shot) to look forward to in the future if the APVMA go through with what is proposed.
And at this stage, as far as I know, there are no other viable knockdown herbicides coming.
Yes there’s glufosinate, but I don’t think it’s going to cut the mustard in Australian conditions, on Australian weeds (pun intended!).
Mechanical
We may need to bring in some mechanical weed kill.
One day, we may need to pull out the full cut sweeps again.
Perish the thought!
But before we get there, we should look at mechanical crop topping.
Windrowing (swathing) followed by harvest weed seed control.
Great option in barley.
But you do need to remember that you will be laying your income on the ground, and you want to be confident of picking it up again, so make sure you consult some experts in this area to give you the best chance of actually harvesting your crop!
The ryegrass will stay in the seed head in the swath, and with good harvester set up, you can deliver it nicely into your awaiting Seed Terminator – or other such implement.
I haven’t tested this against crop topping with glyphosate, but based on what I know, I’m going to say the swath and smash will beat crop topping every day of the week.
Canola is a different story. We often swath above the ryegrass, so it isn’t as effective. And we can’t go spraying paraquat under the swath, it’s off label and likely to cause residue issues.
You’ll have to leave canola with me to come up with some other answers.
Cost
Windrowing costs about $35/ha, plus $15/ha to own and run a Seed Terminator (or thereabouts), so let’s call it $50/ha
Let’s say you have a 3-tonne barley crop at $270/t farm gate price. You run over 3% of it in the crop topping operation, costing $24/ha. The chemical cost is about $12/ha, and the spray operation is around $10/ha. That all adds up to about $46/ha.
The mechanical option costs a little more, and is perhaps logistically more challenging, but it’s a non-chemical option, it works, and if this keeps your rotation going it will be money well spent.
I hope it doesn’t come to this, but given how much we have relied on crop topping feed barley in the past, and the trajectory of glyphosate resistance, I fear that we may need to look at mechanical options like this.
Another additional logistical challenge thanks to herbicide resistance!
At least we have an option.
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.
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