One in six paddocks has glyphosate resistant ryegrass in Australia

5 November 2023 by
Seed Terminator, Kelly Ingram

That’s the recent message from the national herbicide resistance survey.

I reckon glyphosate is probably the biggest herbicide resistance issue facing Australian farmers at the moment.


We have recently scored a heap of new pre-emergent herbicides to give us options when we see resistance to the older ones. Pre-em resistance is still a big issue, and new pre-ems are a little expensive, but now it’s not the biggest issue.

There are just three main knockdown herbicides (four if we include Amitrole, but I don’t think that will ever be a viable option). Glyphosate, Paraquat and Glufosinate.

Glufosinate (e.g. Basta) needs warm weather and high humidity to work well, and it’s pretty soft on ryegrass. We may get it to work with a mixing partner, but it’s no glyphosate.

Paraquat is a great herbicide, but there’s a storm brewing. It has already been banned in about 15 countries (mostly in Europe) due to its acute toxicity, and there are reports of a link to Parkinson’s disease. I’m not a fan of being alarmist and creating fear, but we have to be aware that there is a risk that we may one day lose this herbicide.

But I do believe that glyphosate will still be a very useful herbicide for a long time to come because there are other ways that we can beat ryegrass.

We’ve heard about this glyphosate resistance risk for decades now, it probably took longer to develop than we thought it would, but it’s fair to say it’s here now, and it will get worse.

The national resistance survey is funded by GRDC and involves some great researchers from universities around the country who now all work together to deliver the survey. They jump the fence in about 1500 paddocks around Australia every 5 years, then spend a couple of years testing the weeds. The last fence jumping took place before harvest in 2020, and we’re starting to see the results now.

They sample whatever weeds they find, and you’ll never guess which weed was most prevalent!

Yep, they found ryegrass in about 90% of the paddocks.

Here’s a table that shows the percentage of ryegrass populations where glyphosate resistance was found, and we’re talking about more than 20% of survivors here.


% of paddocks with glyphosate resistance











Well done Tassy, I wasn’t expecting that!

The reason for the concern is that there was a big jump in resistance from the last time the survey was done, and now we are two more seasons down the track from when these samples were taken.

Ok, enough of the fear tactics. What can we do about it?

There is good news. The main weed with glyphosate resistance is ryegrass, and we can beat ryegrass by beating the seed bank.

There are plenty of growers around the country who have had glyphosate resistance problems for 15 years or more and have declared war on the seedbank and won. It’s not easy, life is much easier when all of the herbicides work, but it’s doable.

But, if we lose paraquat, it’s going to get a lot harder, so get stuck into it now while you can, while you have both glyphosate and paraquat as great knockdown options. If we were to lose paraquat, you want to find yourself in the position of having a really low ryegrass seedbank on the day you pick up your last shuttle.

The other good news is that the other weeds find it harder to develop glyphosate resistance than ryegrass, so with good management, glyphosate will still be a useful herbicide for plenty of weeds for years to come.

To find out how to beat the seedbank check out the Big 6 from the good people at Weedsmart. You will notice that harvest weed seed control is number 6 – not because it’s the sixth most important thing to do, but because it comes last in the season.

For my money, I can’t see us farming successfully with high levels of glyphosate resistance without using harvest weed seed control. The fact that we’ve had more money spent on ryegrass than all of the other weeds put together, yet we still find ryegrass in 90% of paddocks shows us that we haven’t been doing enough in the past. 10% of paddocks had no ryegrass. It’s possible.

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Please note this advice is general in nature and not based on your specific circumstances.

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