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Arum lily (Zantedeschia aethiopica)

Introduced as an ornamental, arum lily has escaped cultivation and become a widespread weed, especially in damp habitats. Dense infestations can replace pasture and native understorey, and all parts of the plant are poisonous to people, livestock and pets.

Key facts

Type: Weed, herb.

Native to: Natal and Cape Province, South Africa.

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

Other names: Calla Lily, White Arum Lily, Lily of the Nile, Egyptian Lily.

Best time to act: Flowers are most common from August to November; find and treat actively growing plants, generally from June to September or October depending on the herbicide and flowering.

Identification

  • A robust, clump-forming, fleshy perennial herb that grows to 1.5 metres high.
  • Its glossy, dark green, arrowhead-shaped leaves can reach 600 millimetres long and 300 millimetres wide.
  • The white to ivory, funnel-shaped flower structure surrounds a yellow to orange-yellow spike; the spike can reach 90 millimetres long and the surrounding bract 260 millimetres.
  • Orange ripe berries form in clusters on the lower part of the central spike.
  • Look-alike: Italian arum (Arum italicum) is smaller, has whitish to yellowish leaf veins and a yellowish-green hooded flower bract, and bears orange-red to scarlet berries.

Where it grows

In Australia it is naturalised across many southern areas and grows in damp or marshy places, including wetlands, creeklines, stream banks, pastures, drains and bushland.

Why it matters

  • Dense infestations can replace pasture species and crowd out native plants, particularly in the understorey.
  • In wet habitats, stands can impede water flow and block small streams, creeks and drains.
  • All parts are poisonous to people, livestock and pets, and the plant can irritate human skin and eyes.
  • It is especially toxic to cattle and children, and poisoning has caused fatalities in people and stock.

How it spreads

  • Arum lily spreads by seed and root fragments; a flower head may produce 50 to 500 seeds, and dense stands may have up to 5,000 seeds per square metre.
  • Seeds can be spread by water, birds, foxes, livestock, contaminated soil, machinery and dumped garden waste.
  • Rhizomes usually spread locally by less than 30 centimetres per year, but fragments can be moved farther by garden refuse disposal, cultivation and earthworks.

Control options

  • For scattered plants, remove the whole plant, including all roots and tubers, to reduce regrowth.
  • Larger infestations can be treated with registered herbicides while plants are actively growing; follow-up treatment may be needed to deal with regrowth and seedlings.
  • Mechanical removal works only when all root fragments are removed; repeated rotary hoeing over several years can provide control.
  • Repeat control efforts over several years and check for regrowth and new seedlings.

Hygiene and washdown

  • Remove soil and plant fragments from machinery and gear before leaving an infested site, and avoid moving contaminated soil or dumping garden waste where it can spread the plant.
  • 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: 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: Declared pest (no control category). Declared pest in WA without a control category, so there is no state-wide control requirement, but movement and keeping rules can still apply.
  • 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.

  • 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