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Narrow-leaf cotton bush (Gomphocarpus fruticosus)

Narrow-leaf cotton bush is poisonous to livestock and people, and dense infestations can reduce pasture productivity and grazing capacity. It also invades grasslands, open woodlands and riparian areas, where it can form dense thickets and compete with native plants.

Key facts

Type: Weed, shrub.

Native to: Southern and eastern Africa and the Arabian Peninsula.

Established in: QLD, NSW, VIC, TAS, SA, WA.

Other names: Narrow-leaved cotton bush, Narrowleaf cottonbush, Swan plant, Milkweed.

Best time to act: Look for flowers from August to April, especially in summer, and fruits from February to December; winter slashing can help if seedlings and regrowth are treated before flowering.

Identification

  • This upright perennial shrub usually grows 0.5 to 2 metres tall and has pale green stems that become brown and woody with age.
  • Broken or damaged parts, especially the stems, exude milky sap; the narrow leaves are 4 to 12.5 centimetres long and grow in opposite pairs.
  • White or cream flowers grow in loose, drooping clusters in the upper leaf forks, from spring to early autumn.
  • The light green, balloon-like fruits are 4 to 7 centimetres long and covered in soft spines; they split open when mature.
  • The flattened brown or black seeds have a tuft of long, white silky hairs.
  • Look-alike: Balloon cotton bush (Gomphocarpus physocarpus) is very similar and can grow alongside it, with the two species sometimes hybridising.
  • Look-alike: Narrow-leaf cotton bush has narrowly egg-shaped, slightly curved fruits that taper to a short point, while balloon cotton bush has almost round fruits with an abrupt point, often with a sunken tip.

Where it grows

In Australia it is widely naturalised across southern and eastern regions, especially coastal and sub-coastal eastern New South Wales and south-western Western Australia, and grows on roadsides, disturbed sites, waterways, pastures, open woodlands and fallows.

Why it matters

  • Dense infestations can substantially reduce pasture productivity and grazing capacity.
  • The plant is poisonous to livestock and humans and has caused deaths in cattle, sheep and poultry; contaminated fodder or chaff can be dangerous.
  • Severe gastroenteritis is the main reported symptom of poisoning, and contact with the sap can cause skin rashes and other symptoms in people.
  • It competes with native plants and can form dense thickets in grasslands, open woodlands, disturbed sites and riparian areas.

How it spreads

  • It reproduces by seed, and may also produce suckers from lateral roots close to the soil surface.
  • The fluffy seeds are commonly spread by wind and float on water.
  • Seeds may also spread in agricultural produce such as fodder, or in mud attached to animals, machinery and other vehicles.

Control options

  • Small infestations can be hand-pulled or grubbed because the plant has a shallow root system; remove the crown and as many roots as possible to reduce suckering.
  • Dispose of plant material carefully to avoid spreading seeds, and wear rubber gloves and overalls to avoid contact with toxic sap; wash hands thoroughly before eating.
  • Larger infestations are best managed with a combination of registered herbicides, slashing and pasture management.
  • Winter slashing or mowing can help over time, provided seedlings and regrowth are slashed again or treated with registered herbicides before flowering.

Hygiene and washdown

  • Avoid moving fodder that may contain seeds, and remove mud and plant material from machinery, vehicles and equipment before leaving infested sites.
  • 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: Not a priority weed. Not a state or regional priority weed in NSW. 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: Declared pest (C3). C3 Management: landholders must manage it to reduce its impact and stop it spreading.
  • 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
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • 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

Sources