When you start looking for glyphosate-free weed control, it quickly becomes clear that there’s no one-size-fits-all answer.
Different products work in different ways, and some perform better in New Zealand conditions than others. We’ve already covered a few alternatives — and there are more coming — because shifting away from glyphosate-based weedkillers isn’t about swapping one brand for another. It’s about changing the whole approach.
Slasher Organic Weedkiller is simply one option in that broader mix. It’s widely available, certified for organic use, and has built a bit of a reputation for acting fast. Naturally, people want to know whether it’s worth trying — and how it stacks up against glyphosate-based weedkillers like Roundup, which have dominated the shelves for decades.
A common question we hear is:
“Is Slasher basically the natural version of Roundup?”
It’s understandable why people ask. When a single chemical has shaped how New Zealand gardeners, councils, and land managers think about weeds for nearly half a century, anything new gets measured against it.
But Slasher isn’t a gentler Roundup.
It isn’t trying to be.
And expecting it to behave like glyphosate often leads to frustration.
That’s why it helps to understand what Slasher actually does, how it works, and where the differences lie. Because once you see the two side by side, the comparison becomes far clearer — and the expectations far more realistic.
Before we get into the nuts and bolts of how Slasher compares to Roundup, it’s worth seeing how the makers themselves describe it. Here’s a short overview video that highlights what Slasher is designed to do and where it fits into the weed-control landscape.
You’d expect a promotional video to put its best foot forward — and this one does — but it’s still a useful look at how the product is meant to be used and what results it aims to deliver.
Slasher vs Roundup — What’s the Real Difference?
Most of us grew up thinking weedkillers were all basically the same: spray the plant, wait a bit, and watch it die. Glyphosate-based products like Roundup entrenched that expectation — a kind of “one spray fixes everything” mindset.
Slasher and Roundup, however, sit on opposite sides of the weed control spectrum.
They don’t behave the same in the garden, they don’t interact with soil the same way, and they don’t carry the same risks.
Understanding those differences is the key to knowing when each one works — and when it doesn’t.
How Roundup Works
Roundup is built around glyphosate, a systemic chemical. Once glyphosate is absorbed through the leaves, it travels inside the plant — down the stems, into the roots — shutting down an internal pathway the plant needs to survive. That’s why it can take several days before you see visible results.
The plant dies from the inside out.
How Slasher Works
Slasher takes the opposite approach.
Its active ingredients — pelargonic acid and d-limonene — work on the surface of the plant.
They dissolve the protective waxy layer on the leaves, causing rapid dehydration and collapse. It’s a contact process, not a systemic one, which is why results often appear within hours.
Slasher burns off what it touches.
It doesn’t move through the sap and won’t reach the roots of deep, established plants.
Residue and Soil Impact
Another major difference is what happens after spraying.
Glyphosate residues — and its breakdown product, AMPA — can linger in soil and waterways. That’s part of the ongoing debate among regulators and scientists.
Slasher breaks down far more quickly.
It doesn’t leave the same long-term signature in soil, which is one reason early childhood centres, schools, and councils are taking a closer look at it.
So Which Is “Stronger”?
Neither.
They are built for different jobs.
Roundup takes longer but reaches the roots.
Slasher acts fast but only where it lands.
Two sprays.
Two philosophies.
And two very different expectations.
If Slasher Isn’t Working, Here’s Why
Slasher can be impressive when everything lines up — fast results, visible wilt, and that satisfying “plants collapsing by afternoon” effect. But when it doesn’t perform, most people assume the product itself is the problem.
In fact, many people literally search “Slasher herbicide not working”, because they expect Slasher to behave like glyphosate — and it simply doesn’t.
Because Slasher is a contact herbicide, it only affects the parts of the plant it physically touches. Every leaf needs a good, even coating. If you miss a section — or if the plant has dense growth that the spray can’t reach — those untouched parts will stay green and keep the plant alive. This isn’t a flaw in the product; it’s simply how contact herbicides work.
Moisture is another big factor. In many parts of New Zealand, especially in the upper North Island, the humidity alone can undo a good spray job. Slasher needs dry leaves to work properly, and even early-morning dew can dilute the spray film before it has time to act. If it’s been raining, if the leaves are damp, or if the day never quite dries out, results can be patchy.
Slasher also performs best on smaller or younger weeds. Annuals and fresh shoots respond very well, but larger, woody, or deep-rooted weeds often need a second application. This is where people sometimes get frustrated, expecting a one-spray knockout because that’s what decades of glyphosate marketing trained us to expect. But Slasher isn’t systemic — it won’t travel down into the roots the way glyphosate does — so repeated treatment is simply part of the process for tougher species.
Weather matters, too. Warm, sunny conditions help speed up the dehydration process. On cooler, cloudy days, Slasher still works, just more slowly. If rain arrives soon after spraying, the effect can be reduced or even washed away entirely.
And finally, there’s application rate. Many people under-apply natural weedkillers because they’re trying to be careful. Slasher does best when the leaves are visibly wet. A fine mist won’t cut it; think of it more like giving the plant a thorough surface wash.
All of these factors can make Slasher feel unpredictable if you’re new to it. But once you understand how it works — and why it works the way it does — the results make a lot more sense. And for many New Zealand gardeners, schools, and councils, those trade-offs are worth it for a product that doesn’t leave long-term residues in the soil.
Is Slasher Safe for Humans?
Any time we talk about alternatives to glyphosate, the question of safety naturally comes up. And it’s a fair one. After decades of being told that Roundup was “safe enough to drink,” a lot of people have become understandably cautious about weedkillers in general — natural or otherwise.
A common question we hear is:
“Is Slasher weed killer safe for humans?”
The real answer is a mix of reassurance and realism.
Slasher is often described as a “safer” option, and in many ways it is. Its ingredients — pelargonic acid (a fatty acid found in plants) and d-limonene (a citrus-based oil) — are familiar, naturally occurring compounds. They’re used in everything from food processing to household cleaners. On paper, that sounds reassuring, and to an extent, it is.
But “natural” doesn’t automatically mean harmless. And Slasher is still a weedkiller — its whole purpose is to break down plant tissue quickly and effectively. That means it can also irritate human skin, eyes, and airways if used carelessly. The fact that it’s certified for organic use doesn’t change the basic rule: all herbicides deserve respect.
For everyday use around the home, Slasher is considered low in toxicity when used as directed. It doesn’t have the systemic action or lingering soil footprint that glyphosate-based weedkillers do, and that’s a major reason why schools, councils, and early childhood centres are looking at it more seriously. When residues break down quickly, there’s far less chance of exposure for children, pets, or anyone spending time close to the ground.
But like any product designed to kill plants, it’s not something you’d spray barefoot in shorts and a T-shirt. Gloves matter. Eye protection matters. Spraying on a still day matters. These aren’t “extra precautions”; they’re basic good practice — the same advice we give for any herbicide, whether natural or synthetic.
It’s also worth noting that d-limonene, while naturally derived, can cause skin and respiratory irritation in some people. Sensitive users may want to wear a mask, or at least avoid standing in the drift path.
So is Slasher safe for humans?
Safer than glyphosate-based weedkillers, yes.
Completely risk-free? No.
The key advantage is that Slasher doesn’t bring the same long-term residue or systemic exposure risks that glyphosate does. But it still requires common sense, protective gear, and mindful application — especially around children, food gardens, and enclosed spaces.
Used properly, Slasher offers a practical middle ground: effective weed control without the chemical baggage that’s become impossible to ignore.
Slasher Isn’t a Magic Bullet
Slasher sits alongside a growing list of glyphosate-free options — each with strengths and limits — and understanding that bigger picture is what really matters. It’s one approach, not the solution to everything. And that’s important, because the real opportunity here isn’t to find a perfect, one-spray replacement for Roundup. It’s to rethink how we manage weeds altogether.
Instead of relying on a single systemic chemical that lingers in soil and bodies, more households, schools, and councils are shifting toward methods that are simpler, cleaner, and easier to justify. Slasher fits comfortably into that direction. It acts quickly when used correctly, it breaks down fast, and it avoids the long-term residue questions that continue to follow glyphosate-based weedkillers around the world.
But Slasher is still just one choice among many.
New Zealand has a wider range of alternatives than most people realise — WeedX, Contact Organics, Weed Blast and innovative local options like Weed Blast, along with acetic acid formulas, hot-foam systems, steam weeding, mulching, manual control, and even rethinking how “weeds” fit into our landscapes in the first place. The conversation doesn’t end with Slasher; if anything, it begins there.
Because moving away from glyphosate isn’t about trading Roundup for a different bottle.
It’s about asking better questions, looking at long-term effects, and choosing tools that match the kind of environments we actually want to create.
If Slasher helps start that shift — and helps people realise they do have options — then it’s already doing something valuable. And we’ll keep unpacking more of those options, one by one, until New Zealand has the clearer, more transparent weed-control landscape it deserves.
Disclaimer:
This article is for general information only and isn’t an endorsement of any brand or product. Our goal is to highlight glyphosate-free weed control options so New Zealanders can make informed choices. No More Glyphosate NZ has no financial relationship with the manufacturers or retailers of Slasher or any other alternatives we discuss. As always, we encourage readers to consider their own needs, do independent research, and use any herbicide responsibly.
Image Source & Attribution
The feature image on this page was created using canva.com
