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Yellow oleander (Cascabela thevetia)

Yellow oleander is an introduced ornamental that has naturalised in coastal parts of eastern Australia, especially coastal southern and central Queensland. It can invade bushland and waterways, and every part of the plant is poisonous, particularly the oily seeds.

Key facts

Type: Weed, shrub.

Native to: Tropical America, possibly Peru, Mexico and the Caribbean.

Established in: QLD, NSW, WA, NT.

Other names: Be-still tree, Captain Cook tree, Mexican oleander, Lucky nut.

Best time to act: Look for the plant throughout the year, especially when it flowers in summer and autumn, and treat before fruit matures and seeds can be spread.

Identification

  • It is an upright, spreading, much-branched shrub usually 2.5 to 3.5 metres tall, but can grow as a small tree up to 10 metres.
  • Its long, narrow leaves are spirally arranged along the stems, often clustered near their tips, and have glossy green upper surfaces and paler undersides.
  • Stems and leaves contain poisonous milky sap.
  • Bright yellow, or occasionally pale orange, tubular flowers are 5 to 7 centimetres long and have five petals twisted in the bud.
  • Its large, slightly fleshy fruit has a hard centre, turns black as it ripens, and contains 2 to 4 large, flattened seeds.
  • Look-alike: Yellow bells (Tecoma stans) has compound leaves with toothed leaflets and long, narrow capsules, rather than simple leaves and broad fruit that turns black.
  • Look-alike: Oleander (Nerium oleander) has usually pink, reddish-purple or white flowers and long, cylindrical fruit that splits open to release hairy seeds.

Where it grows

In Australia it grows in tropical and subtropical areas, including waterways, roadsides, waste areas, disturbed sites, old gardens, open woodlands, pastures and coastal environments.

Why it matters

  • It is regarded as an environmental weed in south-eastern Queensland and a priority weed in far northern Queensland, and is considered a potential sleeper weed in other states.
  • It has established in conservation areas, bushland and riparian areas in south-eastern Queensland, and has been reported invading coastal vegetation in northern Queensland.
  • All parts of the plant are very poisonous, especially the oily seeds.

How it spreads

  • Yellow oleander reproduces by seed.
  • Seeds are commonly spread in dumped garden waste, so do not dump fruit or other plant material.

Control options

  • Wear suitable protective gear and avoid contact with the sap, fruit and seeds; all parts of the plant are poisonous.
  • For small plants, remove them carefully with the roots where practical, and contain fruit and plant material so seeds are not spread.
  • For larger plants, use only herbicides registered for the use and follow the product label, or use another method approved for the site; seek a suitably qualified operator where needed.
  • Check for regrowth and seedlings and follow up; contact the relevant state biosecurity agency or local council for current requirements and reporting advice.

Hygiene and washdown

  • Contain fruit and plant material during removal and dispose of it in accordance with local requirements rather than dumping it as garden waste.
  • Clean tools, boots, vehicles and machinery after working in an infestation, and avoid moving contaminated plant material or soil 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: Restricted matter, category 3. Do not give it away, sell or release it into the environment. 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: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • 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
  • 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