One of the great promises of modern agriculture was that herbicides would make weed control simple.
But what happens when the weeds start fighting back?
The Weeds That Won’t Die
Across New Zealand, a quiet but concerning shift is happening in our paddocks. Grass weeds like annual ryegrass, barnyard grass, and summer grass are showing signs of herbicide resistance—adapting to survive chemical treatments that once kept them at bay.
It’s not just speculation. In a 2020 FAR/AgResearch survey, nearly half of arable farms in Canterbury were found to have weed populations resistant to common herbicides, particularly ALS and ACCase inhibitors. More recently, testing in North Island maize fields revealed worrying resistance in Chenopodium album and Digitaria sanguinalis—weeds farmers know well, now becoming harder to kill.
Not Just a Farmer’s Problem
At first glance, this might sound like a niche issue—something for agronomists and cropping contractors to worry about. But herbicide resistance isn’t confined to paddocks or pea crops. When chemicals stop working, the response is often more chemicals—stronger, more frequent, and often more toxic sprays.
And that has ripple effects.
Spray drift doesn’t respect fences. Neither do residues in food or soil. As farmers resort to chemical layering—multiple modes of action, more applications per season—the environmental and human health consequences grow. Glyphosate is often just one part of that cocktail.
Resistance in a Glyphosate World
Glyphosate resistance is already well documented overseas. In Australia and the United States, entire regions have been forced to rethink their cropping systems due to glyphosate-resistant ryegrass and pigweed.
New Zealand, for now, is lagging behind—but not by much.
While few glyphosate-resistant weed populations have been formally confirmed here, signs are emerging. Anecdotal reports from contractors suggest that some populations of summer grass, goosegrass, and wireweed are no longer responding to treatment. And with glyphosate’s dominance in both conventional and conservation tillage systems, the selection pressure is immense.
Are We Spraying Our Way Into a Corner?
The logic is seductive: if one chemical stops working, switch to another. But this chemical arms race is both costly and unsustainable.
Some Canterbury grain farmers are already spending tens of thousands each season trying to keep resistance at bay—investing in more sophisticated spray schedules, rotating chemistries, and adopting expensive pre-emergent options.
But the cycle keeps turning. And sooner or later, the weeds win.
Breaking the Cycle: What’s the Alternative?
Weed scientists and sustainable farming advocates agree: we won’t spray our way out of resistance.
Instead, the solution lies in rethinking our approach entirely:
- Diversity in cropping: Breaking up weed life cycles with rotation, cover crops, and timing.
- Mechanical control: Cultivation, inter-row hoeing, stale seedbeds, and mowing.
- Reduced reliance on herbicides: Using chemicals as a tool, not a crutch.
- Biological and cultural control: Leveraging competition, ground cover, and alternative grazing methods to suppress regrowth.
Ironically, some of the most promising tactics are also the oldest.
A Wake-Up Call for Glyphosate Policy
As New Zealand considers raising allowable glyphosate residue limits in food, perhaps we’re missing the bigger picture. Glyphosate isn’t just a health concern—it’s part of a broken system that relies on chemicals to do the work that nature, rotation, and stewardship once handled.
If glyphosate stops working—or worse, starts failing without anyone noticing—we’re left with few options and fewer excuses.
If We’re Paying Attention…
Herbicide resistance isn’t just a technical issue—it’s a warning. Weeds are adapting faster than our chemical playbook. The question isn’t whether resistance will arrive on our doorstep. It’s whether we’ll be ready when it does.
Maybe it’s time we asked:
What if the real solution isn’t stronger sprays—but smarter systems?
Resources & References
Resistance doesn’t happen overnight—but when it does, it can’t be undone. These resources show how widespread and urgent this issue really is.
AgResearch – Herbicide resistance greater than expected; growing concern
A 2021 AgResearch report found over half of surveyed arable farms and vineyards showed resistance to common herbicides — raising alarms about future weed control
FAR – Herbicide resistance in Canterbury
In a 2019–2020 survey, glyphosate-, Group A- and Group B-resistant ryegrass was confirmed on 13 of 48 cropping farms in the Selwyn District
Weed Science Society of America – Global Glyphosate Resistance
Database of confirmed glyphosate-resistant weed species worldwide.
Herbicide Resistance Action Committee (HRAC)
International collaboration tracking herbicide resistance trends and solutions.
Biological Control of Weeds in New Zealand [PDF]
An overview of NZ’s successful gorse and broom control programs using biocontrol.
Farming Life: Getting to Grips with Herbicide-Resistant Grass Weeds (UK)
Original article that inspired this NZ-focused piece.
The future of weed control may not lie in stronger chemicals—but in learning from the past and investing in more resilient systems.
Image Source & Attribution
We’re grateful to the talented photographers and designers whose work enhances our content. The feature image on this page is by AndrewLozovyi.
