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Khaki weed (Alternanthera pungens)

Khaki weed forms dense mats that can outcompete pastures and native plants, reducing productivity and affecting valuable areas. Its spiny burrs can injure people and animals, contaminate crops and damage wool.

Key facts

Type: Weed, herb.

Native to: South America.

Established in: QLD, NSW, ACT, VIC, SA, WA, NT.

Best time to act: Look for flowers in spring and autumn, and aim to find and treat actively growing plants early in the growing season before they produce seed.

Identification

  • This perennial creeping plant forms dense mats over the ground, with stems that die back in late summer or early winter and regrow from the roots in spring.
  • Its reddish, softly hairy stems grow from a central crown and can reach 60 cm long.
  • Leaves grow in opposite pairs on very short stalks; they are circular or oval, up to 5 cm long, and one leaf in each pair is larger.
  • Yellow-green or green flowers, 8–12 mm long, grow in clusters in the leaf forks and have sharp-pointed hairs.
  • The flowers develop into straw-coloured, prickly burrs about 1 cm long.
  • Look-alike: Gomphrena weed (Gomphrena celosioides) has larger, whitish flowers and no burrs; small matweed (Guilleminea densa) also has no burrs.
  • Look-alike: Paraguay burr (Acanthospermum australe) has hooked burrs rather than spines, while native joyweeds (Alternanthera species) do not have burrs.

Where it grows

In Australia, khaki weed occurs in all states and grows in NSW across a range of climates, including in pastures, grasslands, orchards, roadsides, gardens, parks, stock routes and sale yards.

Why it matters

  • It competes with native plants and can outcompete pastures, reducing productivity.
  • Its burrs can injure people and animals and contaminate crops, including lucerne and hay.
  • It can damage and devalue wool, and is suspected of poisoning sheep and pigs.
  • It can cause hay fever, asthma and dermatitis in some people, and may cause skin, mouth, foot or digestive problems in cattle and staggers in horses grazing where it is abundant.

How it spreads

  • Seeds can remain viable in the soil for up to five years, and spiny burrs spread on livestock and wildlife, shoes and clothing, vehicles and machinery, contaminated produce and moving water.
  • Plants can also grow from stem and root fragments, which may be spread by livestock, vehicles, machinery, cultivators and slashers.

Control options

  • Where possible, control plants at the beginning of the growing season, before they produce seed.
  • Hand-pull or dig small, isolated plants and remove the whole taproot; contact your local council for disposal advice.
  • Deep, repeated cultivation can control plants, but fragments may spread during cultivation and regrow, so check for regrowth and clean equipment thoroughly.
  • Spray actively growing plants with registered herbicides, following label and permit directions.

Hygiene and washdown

  • Check shoes and clothing for burrs and remove them; clean vehicles and equipment after use in infested areas.
  • Avoid driving through infested areas where possible and purchase fodder free of khaki weed.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 1 of 11 regions. Regional priority weed in Murray. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Restricted weed. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class B. Class B: growth and spread must be controlled. All declared weeds are also Class C, so they must not be brought into the NT.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources