Need Fast Weed Burndown?
Diquat is one of the fastest-acting herbicides available. It kills green tissue on contact within hours — but there’s a catch. Here’s what you need to know before choosing a contact herbicide.
Diquat at a Glance
Diquat is a contact herbicide — it kills only the plant tissue it physically touches. Unlike systemic herbicides such as glyphosate, it doesn’t travel through the plant to the roots. This makes it extremely fast but also means perennial weeds can regrow from their root systems after treatment.
How Diquat Works
When diquat hits a leaf surface, it’s rapidly absorbed into the green tissue. Once inside, it interferes with photosynthesis (the process plants use to convert sunlight into energy). This disruption produces reactive oxygen species — essentially, the plant’s own photosynthetic machinery turns against it, destroying cell membranes from the inside out.
The result is dramatic: leaves wilt, brown and dry out within hours. In strong sunlight, the effect is even faster because photosynthesis is more active. On overcast days, the process is slower but still effective.
The critical limitation is that diquat binds to plant tissue so quickly that it never reaches the roots. The molecule is essentially immobilised at the point of contact. This is why contact herbicides like diquat are fundamentally different from systemic products — they can’t kill the entire plant.
When Diquat Is the Right Choice
The biggest practical advantage of diquat is speed plus zero soil persistence. If you need a patch of ground cleared and ready for replanting fast, diquat-based products let you spray today and sow tomorrow. With glyphosate, you’d normally wait 7-14 days for the herbicide to work its way through the plant before disturbing the area.
When Diquat Is NOT the Right Choice
- Perennial weeds: Dandelions, docks, bindweed, couch grass, nettles and thistles all regrow from roots after diquat treatment. You’ll need repeated applications or a systemic herbicide for permanent control
- Brambles and woody weeds: Contact herbicides barely scratch the surface of woody growth. Use fluroxypyr or triclopyr for brushwood
- Lawn weeds: Diquat is non-selective — it’ll kill your grass along with the weeds. For lawn use, you need a selective herbicide such as MCPA or mecoprop-P. See the best weed killer for lawns guide
- Long-term weed control: Because diquat has no soil activity at all, new weed seeds germinate freely after treatment. It provides no residual control
Diquat vs Other Herbicides
Diquat and pelargonic acid are both contact herbicides with similar speed, but diquat is a synthetic chemical while pelargonic acid is derived from plant fatty acids. For gardeners wanting a more natural option with the same fast-acting contact kill, pelargonic acid is the alternative — though neither will kill roots.
For most garden situations where you need permanent weed removal, glyphosate remains the more effective choice despite being slower. If your weed killer doesn’t seem to be working, patience is often the answer with systemic products — check our timing guide for realistic expectations.
Availability and Regulation in the UK
Diquat’s availability to home gardeners has changed significantly in recent years. While it remains approved for professional and agricultural use in the UK, consumer-grade products containing diquat have become harder to find. Most ready-to-use “fast acting” weed killers on garden centre shelves now use pelargonic acid or acetic acid (vinegar-based) as the active ingredient instead.
Diquat is related to paraquat — once one of the world’s most widely used herbicides, banned in the UK and EU since 2007 due to its extreme toxicity to humans. Diquat is considerably less toxic than paraquat, but the regulatory trend has been towards restricting bipyridylium herbicides generally.
If you’re looking for fast contact herbicide action in a consumer product, pelargonic acid is the most widely available alternative. It works on the same principle — contact destruction of green tissue without root kill — and is available in most garden centres.
Frequently Asked Questions
Is diquat the same as paraquat?
No. They’re related chemicals in the same bipyridylium family and both work as contact herbicides, but paraquat is far more toxic to humans and has been banned in the UK since 2007. Diquat remains approved for use but is primarily restricted to professional and agricultural applications.
Can I buy diquat for my garden?
Consumer products containing diquat have become rare in UK garden centres. Most fast-acting garden weed killers now use pelargonic acid instead. Professional users can still source diquat-based products through agricultural suppliers.
Will diquat kill the roots of perennial weeds?
No. As a contact herbicide, diquat only kills the plant tissue it physically contacts. Perennial weeds with established root systems will regrow after treatment. For permanent removal of deep-rooted weeds, you need a systemic herbicide like glyphosate.
How quickly does diquat work?
In good conditions (warm, sunny weather), you can see wilting and browning within 1-3 hours. Complete burndown of treated foliage typically occurs within 24-48 hours. This is dramatically faster than systemic herbicides, which can take 7-21 days to show full effects.
Can I reseed after using diquat?
Yes, and this is one of diquat’s main advantages. Because it deactivates on contact with soil and leaves no residue, you can reseed or replant within 1-2 days of application. Just wait until the treated foliage is completely dead and remove the debris.
Is diquat safe for pets?
Keep pets off treated areas until the spray has completely dried (typically 2-4 hours). Diquat is toxic if ingested in concentrate form. Always store products securely and follow the label safety instructions.
Looking for Effective Weed Control?
For permanent weed removal, systemic herbicides outperform contact products. Our weed killers range includes glyphosate-based treatments that kill roots and prevent regrowth.
