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Arum lily

Arum lily is a large perennial herb that threatens environments with waterways. It displaces native plants and is toxic to people, livestock and pets. Arum lilies are planted in gardens in the Green Adelaide region.

Description

Arum lily also known as the Calla lily, is a tall erect perennial (long lived) herb with large green leaves, growing from a thick fleshy rhizome (rooting tuber), which can persist indefinetly. It prefers moist areas and will tolerate water flow and intermittent submergence. Plants can grow to 1.5 m tall.

Arum lillies, white sheath around yellow flowers and dark green leaves
Dense stands of Arum lily can affect water flow and, displace native species. Plants are toxic to humans and animals. Photo: P. Watton

The distinctive large arrowhead shaped leaves are hairless, growing up to 50 cm long on fleshy stems. The above ground growth dies off late summer after flowering each year before growing back in autumn.

Arum lily flowers mostly in spring and early summer. Small flowers form on a distinctive yellow spike in the centre of one large white funnel-shaped sheath that is slit to the base, spreading open in the upper part and arching back to a centred point.

Fruit forms on the spike as a cluster of green berries, turning orange to yellow when mature. Each fruit produces on average 4 seed. Seed are yellow-brown 3 mm wide and wrinkled when dry. Seed remain viable in the soil for less than one year.

Image of arum lily with large white sheath
The large white sheath wraps the yellow spike on which flowers and stamen form producing berries. Photo: H.Storch

Impacts

Arum lily can form dense stands along watercourses or in swampy sites, and may displace all understorey species at the site. Arum lily can invade pasture areas impacting on productivity, particularly in low lying damp areas.

Arum lily is toxic, and if ingested by stock or pets can be fatal. Cases of poisoning are rare as arum lily is unpalatable. The plant can also cause eczema and allergic reactions in people.

Distribution

Arum lily originates from South Africa and is a popular garden plant in the Green Adelaide region. If it escapes gardens, it can invade watercourses, wetlands and damp sites in pastures.

Spread of arum lily by humans is often through deliberate planting and/or illegal dumping of garden waste.

Most seed are dispersed by birds with foxes and stock also aiding in the spread. Seed is also moved downstream by water.

Management

Arum lily (Zantedeschia aethiopica) is a declared weed under the Landscape South Australia Act 2019.

To prevent the spread in the Green Adelaide region, the sale of this plant or contaminated goods is prohibited and the movement of either on a public road is restricted. Land owners must take reasonable steps to control plants on their property.

We encourage control of plants where there is a risk to human health, agriculture, and biodiversity. Undertaking weed control needs to be done carefully to prevent damage to native vegetation.

Individual plants can be dug out any time anywhere, using a shovel, trowel, or pitchfork. Ensure all rhizomes (rooting tubar) are collected as these will reshoot.

For large infestations machinery can be used but should be avoided wherever possible to reduce the risk to biodiversity or irreparable damage to the site. If excavating material or removing vegetation from within a watercourse a Water Affecting Activity permit may be required. For more information go to www.greenadelaide.sa.gov.au/discover/water-plans- permits

Removal of flowers will prevent seed set and seed dispersal by birds.

Always wear protective clothing when handling the poisonous arum lily (long pants and sleeves, boots and

gloves). Avoid contact with mouth and skin. Wash hands after contact.

Chemical

While plants are actively growing, apply herbicide (weed killer) by wiper, brush or spot spray ensuring good leaf coverage and before berry set. Take care to avoid non target plants. Herbicide can also be applied to cut stumps with a sponge applicator bottle.

This is suitable for use in conservation areas, bushland and other non-crop areas.

Correct application of the appropriate herbicide is very effective at killing arum lily however, the small rhizomes attached to the main tuber are not always killed by the herbicide application. Follow up control is essential. Plants growing from the surviving rhizomes are not usually visible until two years after the initial spraying.

For advice on chemical options please refer to Controlling declared weeds in SA from PIRSA.

Observations of weeds can be entered into iNaturalist, an app which can assist with identification.