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What are Perennial Weeds?

Perennial Weeds are longer lived plants that can survive winter or regrow from roots, rhizomes or tubers in spring after a period of dormancy.

Many weeds that grow from seed can be both annuals and perennials, depending on their age, maturity and root development.

The longer life span is what distinguishes Perennial Weeds from Annuals which usually grow only from seed produced in the previous growing season and die after a year.

Effective weed control depends on being able to identify three things: whether a weed is a Grass, Broadleaf or Sedge type, an Annual or a Perennial, and whether it actively grows in warmer or cooler seasons.

The combination of these three factors will determine the best timing, method and products to use.

Identifying Perennial Weeds

A weed is loosely defined as any plant growing in the wrong place, which largely depends on your location and personal preferences. The exception is a range of highly invasive or noxious weeds that are banned in various states.

Here’s a list of common Perennial Grassy weeds to look out for:

  • African Lovegrass – A hardy drought tolerant grass that grows in clumps and has stems up to 1.2m. Seed heads have many branches with lots of grey-green or purplish coloured elongated flower spikelets.
  • Carpet Grass – A vigorous creeping warm season grass with wide leaves and blunt tips. It is commonly used in parks, roadsides and golf course roughs in tropical and subtropical areas, but will quickly crowd out other types of grass in your lawn.
  • Johnson Grass – An erect grass that grows up to 2m tall and has alternate leaves up to 50cm long with a pronounced pale mid-vein. The underground stems are white and seed heads turn reddish black when mature.
  • Kikuyu – An aggressive coarse grass that spreads by runners and has hidden seed heads. It forms dense mats and is regarded as an environmental weed in the five mainland states.
  • Onion Grass – Also known as Guildford Grass, it is a thin wiry weed that grows from a corm and produces small purple flowers with six petals.
  • Parramatta Grass, Rat’s Tail Grass – An upright, tussocky grass, with hairless stems that carry numerous densely packed flower spikelets and oval seeds that turn reddish brown as they mature.
  • Paspalum – A tufted grass with slightly folded leaf blades that grows from spring to autumn. The sticky seed heads are up to 10cm long and arranged along a thin stalk.
  • Summer Grass – Also known as Crabgrass, this annual weed thrives in heat and humidity. Leaves are grey-green, stems can be red or brown and it spreads via runners. The seed heads contain small spikes.

Common Perennial Sedges to look out for are:

  • Mullumbimby Couch – Grows year round, producing bright green leaves and pale green seed heads on three-sided stems up to 40cm long. It has long underground runners.
  • Nut Grass – Grows all year round, with long narrow leaves and puts out erect spikelets of red-brown or purple-brown flowers on triangular stems. It produces a network of creeping underground stems with small tubers.

Common Broadleaf Weeds to look out for include:

  • Bindii – A low-growing weed with carrot-like leaves, it has creeping hairy stems and in spring develops fruit that dry to become prickly burrs.
  • Catsear Weed – Often mistaken for Dandelions, it has hairy leaves and produces tall stalks that can have multiple small yellow flowers.
  • Dandelion Weed – The rosette of toothed leaves lays flat on the ground and plants put up a hollow stalk with a single bright yellow flower that becomes a puffball of seeds. Broken stems and leaves ooze a milky substance.
  • Dock Weed – A perennial with large oval green leaves that have a distinct mid rib. Tap roots can be very long, up to 90cm, and they produce large numbers of seeds. Often found growing near nettles and rubbing a crushed leaf on nettle stings can help ease the pain.
  • Dollar Weed – Also known as Pennywort, has bright green, glossy rounded leaves with wavy edges, that look like small lilypads. Tiny star-shaped white flowers grow in umbrella-like clusters.
  • Khaki Weed – Also known as Khaki Burr, it is a low-growing perennial with oval-shaped leaves that grow in pairs on short stalks, and hairy reddish stems up to 60cm long. Mature flowers in the leaf forks develop sharp points and prickles.
  • Onion Weed – The tall thin leaves and stems smell like onions or leeks when rubbed or broken. It puts out mostly white bell-shaped flowers at the top of a long stalk.
  • Oxalis – Also known as Creeping Oxalis, it has small heart-shaped leaves and produces tiny yellow flowers. It spreads by putting out runners and can regrow from the roots.
  • White Clover – The bright green leaf on each stem is split into three leaflets with a paler moon-shaped mark. Flowers are made up of lots of small tubular flowers growing from the centre in a pom pom shape.

How to Control Perennial Weeds in Your Lawn

Staying a step ahead of weeds by controlling them when plants are small is essential for ensuring the good health of your lawn.

It’s possible to safely manage weeds using chemical or natural methods, or a combination of the two.

Using a Herbicide

Perennial grass weeds can be some of the most difficult to manage because there’s a limited range of selective post-emergent herbicides available for domestic use.

Look for products containing the active ingredient Halosulfuron-methyl or a blend of Clopyralid, Diflufenican and MCPA.

In some cases, careful spot treatment with a non-selective contact herbicide, such as glyphosate, can be the only effective option for achieving knockdown.

In areas with a known problem, pre-emergent herbicides containing the active ingredient Prodiamine can be useful for stopping newly-germinated seeds in their tracks.

You can read our guide to Using Pre-emergent Herbicides here.

Broadleaf Weeds are usually easier to identify and there’s a wider range of options, including selective and broad spectrum herbicides.

Always check the product label to make sure it is effective on the weed you’re trying to control and safe for use on the type of grass in your lawn. Buffalo lawns are especially sensitive to some herbicides.

Recommended Products

Spartan 500ml

Spartan 500ml is one of the leading pre-emergent herbicides for the control of Crowsfoot Grass, Summer Grass, Winter Grass, Paspalum and other grassy weeds. It is suitable for use on Zoysia, Kikuyu, Couch and Buffalo grasses.

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Indigo Duke 100WG 100gm

Indigo Duke 100WG 100gm is a very effective post-emergent liquid herbicide that controls certain broadleaf weeds and Winter Grass through suppression. Indigo Duke 100WG should only be used on Kikuyu, Buffalo and Couch grasses.

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Indigo ProForce Contra M 1L

Indigo ProForce Contra M 1L is a reliable, selective liquid herbicide used to control numerous broadleaf weeds, including burr medic. It cannot be used on Buffalo lawns, but is suitable for use on Zoysia, Kikuyu and Couch grasses.

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Bow and Arrow 500mL

Bow and Arrow 500mL is one of the most effective broadleaf liquid herbicides on the market. Suitable for Zoysia, Kikuyu, Couch and Buffalo grasses however transient discolouration may occur on Kikuyu, Carpet and Queensland Blue Couch lawns.

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Barricade 1L

Barricade 1L is a pre-emergent liquid herbicide that controls a wide range of grass and broadleaf weeds and is suitable for use on Zoysia, Kikuyu, Buffalo and Couch grasses.

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Oxadiazon Oxafert 16-2-6 20kg

Oxadiazon Oxafert 16-2-6 20kg is a combined Fertiliser and pre-emergent Herbicide product for the control of Summer Grass, Crowsfoot Grass, Winter Grass and Creeping Oxalis and application of an NPK Fertiliser. It is suitable for use on Zoysia, Kikuyu, Couch and Buffalo.

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When to Apply Weed Killer

The best time to apply post-emergent herbicides is when weeds are small and actively growing.

In the case of summer broadleaf weeds, this will be spring, or autumn for winter broadleaf weeds.

Pre-emergent herbicides should be applied before weed seeds germinate, which is usually in early spring.

There’s more information about correctly applying herbicides here.

How Long do Weed Killers Take to Work?

The speed at which grass weeds die following the application of a herbicide can depend on several factors, including the type of herbicide used, weed maturity, the size of the infestation, and the health of your lawn.

If applied correctly, you will start to see the effects of some weed killers within 48 hours of spraying, while others might take 2-3 weeks.

The weeds may take longer to die off completely and may require subsequent applications 6-8 weeks later for large, persistent weed infestations.

Getting Rid of Perennial Weeds Naturally

There will be times when manual removal of weeds is the best, cheapest or safest method of control.

When weeds are small or there’s only a few of them, it makes more sense to pull them up by hand than going to the trouble of mixing and spraying a batch of herbicide then properly disposing of the leftover mixture.

Other scenarios include new lawns, which are more vulnerable to chemical damage than established lawns, and when weeds are growing in Soft Leaf Buffalo lawns which are more sensitive to herbicides than most other grasses.

You can read our complete guide to pulling weeds from your lawn here.

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