How to Kill Onion Weed & Guildford Grass in Australian Lawns

Onion Grass (also known as Guildford Grass) and true Onion Weed are actually different plants, but they share one thing in common: they are incredibly stubborn. Here is how to wipe out both.

 🧪 Understanding the Weeds You’re Dealing With

Onion weed and onion grass / Guildford grass are some of the toughest lawn weeds in Australia because:

• They grow from a bulb which stays alive even if the top is removed.
• Pulling it out doesn’t work, the bulb snaps off and multiplies.
• Typically appears in autumn, winter and spring producing slender stems and sometimes purple flowers.
• Very difficult to mow off

Because of this, the only reliable control method is a systemic herbicide that moves into the bulb.

🌱 Why Odessa Herbicide + Wetter 600 Works

Odessa Herbicide + Wetter 600 Surfactant, contains a sulfonylurea active that is designed to:

• Translocate into the bulb/corm, killing the weed at its source.
• Provide selective control, meaning it targets the weed without damaging couch, kikuyu, or buffalo when used as directed. NOT recommended on QLD Blue Couch.
• Work on both broadleaf and grassy weeds, including Guildford grass.

The included Wetter 600 improves leaf coverage and penetration, very beneficial for waxy, upright weeds like onion weed.

✅ Best Practice Application Guide

To maximise results when using Odessa Herbicide + Wetter 600:

1. Apply When Weeds Are Actively Growing: Onion weed and Guildford grass grow strongest in autumn–winter, making this the ideal treatment window.

2. Use the Correct Mixing Rate: Follow the label exactly. Sulfonylurea herbicides work at very low rates, more is not better.

3. Always Add the Surfactant: Mix Wetter 600 thoroughly into your spray tank to ensure the chemical clings to the waxy blades.

4. Spray, Don’t Spot‑Pull: Never spot-pull these weeds. Foliar spraying is the only way to deliver the active ingredient to the underground roots.

5. Expect a Slow Kill (4–6 Weeks): Bulb-based weeds die gradually. Expect a slow, total kill over a one-month period as the chemical works its way downstairs.

6. Time Your Mowing: Avoid mowing your lawn for 3 to 4 days before and after spraying. This ensures maximum leaf surface area to absorb the treatment.

7. Re‑treat the Following Season if Needed: Deeply embedded bulbs or massive, long-term infestations may require a follow-up treatment

🛑 Common Mistakes to Avoid

• Do not use hose‑on sprayers, they dilute the herbicide too much and reduce accuracy.
• Do not apply during extreme weather or frost, uptake will be poor.
• Do not blanket spray newly laid turf, wait until fully established.

🌿 Summary: The Secret to a Weed-Free Lawn

Odessa Herbicide + Wetter 600 is one of the most effective, homeowner-accessible solutions available in Australia. By targeting the underground bulb instead of just burning the leaves, you stop the regeneration cycle entirely. Apply during active growth, use a surfactant, and give the process 4 to 6 weeks to completely clear your turf.

People Also Ask

Why is onion grass so hard to kill?

Onion grass (and true onion weed) is incredibly difficult to eradicate because of its complex underground survival system. The plant grows from a central bulb surrounded by dozens of tiny, dormant "bulblets" or offsets. Standard weed killers only burn off the top leaf, leaving the bulbs completely unharmed. To make matters worse, the leaves have a glossy, waxy coating that causes regular liquids to slide right off without being absorbed.

Can you pull out onion weed by hand?

No, you should never pull onion weed or onion grass out by hand. While it might look clean on the surface, pulling the plant triggers a defense mechanism that detaches the tiny underground bulblets from the main root. These bulblets stay behind in the soil, and pulling effectively "plants" dozens of new weeds, making your infestation much worse. The only way to permanently remove it is with a systemic herbicide that penetrates and kills the bulb system entirely.

What is the best selective herbicide for Guildford grass?

The most effective selective herbicide for controlling Guildford grass (onion grass) in Australian lawns is professional products like ProForce Duke 100WG and Odessa Herbicide. This powerful systemic herbicide is safely tolerated by common lawn types like Buffalo, Couch, and Kikuyu, but targets the weed down to the bulb.

Pro Tip: Because Guildford grass leaves are so waxy, you must mix a high-quality surfactant (like Wetter 600) into your sprayer. The surfactant breaks the surface tension, forcing the herbicide to stick to the leaf and penetrate down to the bulbs.

Mighty Goat Lawns 🐐

Published by: Vedran Malic