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Crofton weed (Ageratina adenophora)

Crofton weed is a fast-spreading shrub that invades disturbed land and can reduce crop and pasture productivity. It is poisonous to horses and can cause severe lung and heart damage, and death.

Key facts

Type: Weed, shrub.

Native to: Mexico.

Established in: QLD, NSW, VIC, SA.

Best time to act: Look for the white flower clusters in spring and treat actively growing plants before they flower.

Identification

  • An erect, perennial, multi-stemmed shrub, usually 1–2 m tall.
  • Leaves are dark green, slightly crinkled and triangular to diamond-shaped, with toothed edges and pointed tips; they grow in opposite pairs.
  • White flowers, 5–8 mm in diameter, form clusters at the ends of stems and are present in spring.
  • Young stems are soft, hairy and reddish to purplish brown; older stems become woody, smooth and grey.
  • Look-alike: Mistflower has narrower, spear-shaped leaves, is usually shorter at 30–100 cm, and sprawls rather than growing upright.
  • Look-alike: Siam weed is a sprawling shrub or climber, with smaller flowerheads that may be pale blue-lilac, pink-mauve or white.

Where it grows

In Australia, it grows mainly along the NSW east coast as far south as Wollongong, is more common further north, and also occurs in isolated infestations on the Northern and Central Tablelands, especially on disturbed sites.

Why it matters

  • It is poisonous to horses; grazing it for as little as eight weeks can cause sickness, and poisoning can lead to respiratory failure and death.
  • It reduces crop yields and competes with pasture grasses, reducing productivity.
  • It outcompetes native plants and reduces habitat and food for native animals.

How it spreads

  • Mature plants can produce 10,000–100,000 seeds per year; the seeds need light to germinate, so infestations are more likely on bare or disturbed ground.
  • Seeds spread by wind and water, in contaminated agricultural produce and soil, and in mud on vehicles, machinery, animals, boots and clothing.

Control options

  • For small, scattered plants, pull or dig them out and remove the crowns to prevent regrowth.
  • Slashing can reduce flowering, seed production, vigour and density; avoid slashing flowering or seeding plants, and maintain competitive pasture where possible.
  • Use herbicides registered and labelled for the site and target weed, following label directions; treat actively growing plants before flowering.
  • Check treated areas for regrowth and new seedlings and control them; contact your local council weeds officer for identification and technical advice.

Hygiene and washdown

  • Remove mud and soil from vehicles, machinery, boots and clothing before leaving infested areas.
  • Avoid moving contaminated soil or agricultural produce to clean areas.
  • 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 Hunter. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • 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: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • 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
  • 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

Sources