Arum Lily, Zantedeschia aethiopica, was introduced to WA from South Africa more than 100 years ago as a garden plant. It is now a widespread and well-established weed, and the sale or propagation of this declared pest has been prohibited since 2006. It thrives in the moist conditions of the Southwest, where it chokes out native vegetation and invades pastures. Contact with Arum Lily can cause eczema in humans, and ingestion is toxic to animals, with stock losses documented. It spreads by growth of underground tubers, and by seed dispersal via birds.
TIP: In WA, landowners are required to control Arum Lily on their property.
Mechanical removal (multiple rotary hoeing over several years) may be effective, but only if all the root fragments are removed. Control is usually achieved through herbicide application. Metsulfuron (0.2g in a 10L backpack sprayer, or 20g/hectare) is applied, with a wetting agent (Pulse, others) added at 1:400 dilution. Glyphosate is not effective against Arum Lily.
TIP: Add a red dye to the mix; the pink blossoms will mark your progress.
Optimal time to spray is June-October, when the flowers are in bloom. Metsulfuron is effective in very dilute concentrations, and degrades rapidly in the environment. The wetting agent can be harmful to amphibians however, so steer clear of frog habitats while spraying.
TIP: The bad news is that the spraying needs to be repeated several years in a row to be effective.
On a recent Sunday, 3 NCI volunteers assisted Nullaki landowner Tom Wang in spraying 155L of herbicide on 3 large infestations in the bush, along a road verge, and in a paddock. We hope to treat even more areas as our window of opportunity fades.
TIP: If you can’t get to that last patch, cut off and destroy the flowers to prevent seed dispersal.
For more information, visit: https://www.agric.wa.gov.au/declared-plants/arum-lily-declared-pest