Winter Weed Control in Perth

Winter Weed Control · Perth, WA

Your Last Chance to Stop
Winter Weeds.

By Lawn Doctor Turf Solutions  ·  May 2026  ·  Perth, WA

Every year, Perth homeowners spend hours in June and July pulling weeds out of their lawn by hand. Spraying. Spot treating. Watching the wintergrass spread from one end of the lawn to the other. And every year the answer is the same: they missed the window.

Pre-emergent herbicide is the most cost-effective weed control available. A single application in May stops an entire generation of winter weeds before they break the surface. But it only works on seeds that haven't yet germinated. Once you can see the weeds, that application is useless for this season.

In Perth, the germination window for the main winter weeds opens when soil temperatures drop into the 10 to 15 degree range. That typically happens in late May. We are at that point right now.

The Short Answer

Apply a pre-emergent herbicide this weekend. If you haven't already, this is your last reliable opportunity before wintergrass, crowsfoot and oxalis germinate in your lawn. Once they're up, you're managing them reactively for the rest of the season.

If you already applied OxaFert as part of your autumn program, you're covered. If not, read on.

Wintergrass is one of the most common and persistent lawn weeds in Perth. Pre-emergent herbicide applied now stops germination before it starts.

The three winter weeds that matter most in Perth

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Wintergrass

The most widespread winter weed in Perth. Germinates in cool moist soil and spreads rapidly through seed. Produces a light green, fine-bladed clump that is highly visible in a lawn. Extremely difficult to remove once established without damaging surrounding turf.

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Crowsfoot Grass

A low-growing grass weed with distinctive finger-like seed heads. Thrives in the cooler months and competes aggressively for the nutrients and moisture your lawn needs to hold colour through winter. Particularly common in lawns with thin or stressed areas.

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Oxalis

Clover-like broadleaf weed with a distinctive yellow flower. Spreads through both seed and underground bulbils, making it one of the harder winter weeds to control once established. Pre-emergent is significantly more effective than post-emergent treatment for oxalis.

Why pre-emergent works and why timing is everything

Pre-emergent herbicide works by creating a chemical barrier in the top layer of soil that prevents germinating seeds from establishing a root system. It has no effect on established plants and no effect on seeds that have already begun to germinate. Its entire effectiveness depends on being in the soil before germination occurs.

This is what makes the timing so critical. Apply it too early and the barrier breaks down before the germination window opens. Apply it too late and the seeds have already moved past the point where the herbicide can intercept them. The mid-to-late May window in Perth is when the conditions align correctly for the most effective application.

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The Soil Temperature Rule

Most winter weed seeds germinate when soil temperature drops consistently below 15°C. Perth's soil typically reaches this point in late May. Once germination begins, the pre-emergent window is closed for that generation of seeds. Applying now gives the barrier time to establish before soil temperatures reach the germination threshold.

Pre-emergent vs post-emergent: understanding the difference

These are two fundamentally different types of herbicide and they are not interchangeable.

Pre-emergent herbicide prevents germination. It goes into the soil before weeds appear and stops seeds from establishing. It will not kill weeds you can already see. Apply it now, while the lawn still looks clean.

Post-emergent herbicide kills established weeds. It is applied to visible weeds after germination. It is more labour-intensive, less effective on species like oxalis, and does nothing to prevent the next generation of seeds from germinating.

The ideal approach is to use both in sequence. Pre-emergent now, before germination. Selective post-emergent in June or July if any weeds break through despite treatment. But if you only do one, the pre-emergent applied this weekend does more work than months of post-emergent spot spraying later.

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Important

Never use a non-selective herbicide such as Glyphosate near established turf. Non-selective herbicides kill everything they contact, including your lawn. Always use a selective herbicide formulated for use in turf, or a dedicated pre-emergent product applied to the soil rather than the leaf.

How to apply pre-emergent correctly

1

Mow the lawn first

Mow to your regular height before applying. This removes any debris that could intercept the product and ensures even coverage of the soil surface.

2

Apply evenly across the entire lawn

Use a rotary spreader for granular products or a calibrated sprayer for liquid. Uneven application leaves gaps where weeds can germinate. Overlap slightly on each pass to ensure full coverage.

3

Water in immediately

Pre-emergent herbicide must be watered into the soil to activate. Apply on a watering day or water manually straight after spreading. Without moisture, the active ingredient stays on the surface and does not form the soil barrier it needs to be effective.

4

Do not disturb the soil after application

Avoid aerating, dethatching or anything else that disrupts the soil surface for at least four weeks after application. Breaking the barrier layer reduces effectiveness significantly.

5

Spot spray any visible weeds separately

If you already have some winter weeds showing, spot spray them with a selective post-emergent herbicide appropriate for your turf type before or after the pre-emergent application. The pre-emergent will not affect established plants.

Variety-specific notes

Variety	Pre-Emergent Notes
Sir Walter Buffalo	OxaFert is fully compatible with Sir Walter and is one of the most popular pre-emergent applications for this variety in Perth. Apply at the standard rate and water in well. Do not use products containing Simazine on Sir Walter as it is sensitive to this active ingredient.
TifTuf Hybrid Couch	Compatible with both OxaFert and Barricade. TifTuf's aggressive growth provides some natural weed suppression once established, but pre-emergent is still recommended for winter weed control particularly in newly laid or thinned areas.
Zoysia Australis	Zoysia's dense growth habit gives it excellent natural weed resistance once fully established. Pre-emergent is most important in the first two winters after establishment or in any areas that have thinned. Check product compatibility on the label.
Nullarbor Couch	Compatible with standard pre-emergent applications. Apply at the standard rate. As with all couch varieties, ensure the product is labelled as safe for use on couch turf before applying.

OxaFert combines a pre-emergent herbicide with a granular fertiliser in a single application. Two jobs done this weekend instead of one.

Recommended products

Two options depending on whether you want a granular application that also fertilises, or a liquid pre-emergent for denser or thatchy turf.

Pre-Emergent Herbicides

Pre-Emergent + Fertiliser

OxaFert

The most popular choice for Perth homeowners. Granular pre-emergent herbicide combined with fertiliser in a single application. Stops wintergrass, crowsfoot and oxalis germinating while feeding the lawn at the same time. Spread like a standard fertiliser and water in. Compatible with all Lawn Doctor varieties except as noted above.

Shop OxaFert

Liquid Pre-Emergent

Barricade

A liquid pre-emergent herbicide that penetrates more effectively in dense or thatchy turf where granular products can struggle to reach the soil surface. Applied through a sprayer. Better choice for lawns with heavy thatch or where granular distribution has been uneven in past seasons.

Shop Barricade

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Did You Apply OxaFert Last Week?

If you applied OxaFert as part of your May fertilising program, you're already covered for pre-emergent this season. The active ingredient in OxaFert provides pre-emergent weed control as part of the same application. No second treatment needed.

Don't miss the window

Stop winter weeds
before they start.

OxaFert and Barricade are both available online with delivery across Perth, or in store at our Wangara showroom. Apply this weekend while the window is still open.

Shop OxaFert All Lawn Care Products