Arum Lily

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How to Kill Arum Lily in New Zealand

Botanical name: Zantedeschia aethiopica  |  Also known as: Calla lily

Quick answer:

Arum lily is a clump-forming, damp-loving weed with large glossy leaves and a white flower around a yellow spike. It's hard to kill because it regrows from tough underground rhizomes, so a single spray rarely finishes the job. The most reliable control is a foliar or cut-stump herbicide treatment during active growth, followed by a second treatment on any regrowth.

• Look for large, arrowhead-shaped glossy leaves and a white funnel-shaped flower with a yellow central spike
• Spreads by seed and by underground rhizomes, which is why it keeps coming back after one treatment
• Best treated with a metsulfuron-methyl + glyphosate + penetrant mix on healthy, actively growing leaf, spring through late autumn
• Commonly grows in drains, wetlands and stream margins, so herbicide label restrictions around water bodies must be followed

Arum lily is one of the most common damp-ground weeds Kiwi farmers, contractors and lifestyle block owners run into, especially anywhere the ground stays wet through winter. It looks tidy enough in a garden bed, but once it gets into drains, wet paddocks or stream margins it spreads fast and is genuinely tough to shift for good. Here's what it is, why it keeps coming back, and how to control it properly.

How to Identify Arum Lily

Native to southern Africa, arum lily (Zantedeschia aethiopica) is an evergreen, clump-forming perennial with large, glossy, arrowhead-shaped leaves and a distinctive white, funnel-shaped flower (technically a spathe) wrapped around a bright yellow central spike. Clumps typically stand 1 to 1.5 metres tall where growing conditions are good.

Leaves are dark green, leathery, arrowhead-shaped and can reach up to 45cm x 25cm, with individual leaf stalks as long as a metre. Flowering usually runs from August through to late January, though it can occur outside that window. As the flower dies back it produces berries around 1cm across, green to yellow (orange-yellow on some variants), spread to new sites by birds, animals and flowing water. Below ground, the plant grows from a tuber with fleshy white roots, and it's this tuber and root system, not the seed, that lets an established clump persist and expand in place year after year. Once established it tolerates most soil types and is drought resistant and long-lived.

Why Does Arum Lily Keep Coming Back?

Because killing or removing the leaves and flowers doesn't mean the plant underneath is dead. Arum lily persists through substantial underground rhizomes and tuberous root structures, and any viable piece left behind can resprout.

This is why a single herbicide treatment often isn't enough on an established Zantedeschia aethiopica clump. Current NZ guidance is consistent on this: Bay of Plenty Regional Council recommends two herbicide treatments on established plants, one early in the season to stop flowering and a follow-up later to deal with resprouting rhizomes. Environment Canterbury takes the same approach, recommending regular follow-up checks on previously treated sites. Mowing or slashing alone does nothing to the rhizomes below ground, so it won't control the plant either, it just removes the visible top growth for a while.

Plan on treating, then coming back to check for regrowth, rather than expecting one pass to finish the job.

Where Does Arum Lily Grow in NZ?

Arum lily favours damp, low-lying ground and is most common through the North Island, with scattered occurrences further south.

• Drains, ditches and stream margins
• Wetlands and swampy pasture
• Low-lying wet paddocks and pugged ground
• Damp, disturbed forest margins and gullies
• Garden waste dump sites, where discarded rhizomes take root and spread into the wild

Because so much of its habitat overlaps with waterways, controlling it well means paying close attention to herbicide label restrictions around water. More on that below.

Is Arum Lily Poisonous?

Arum Lily vs Green Goddess

They're closely related, and control methods are identical for both, but Green Goddess and ordinary white arum lily aren't treated the same way under NZ biosecurity rules. The National Pest Plant Accord specifically names the 'Green Goddess' form of Zantedeschia aethiopica, a green-and-white flowered cultivar, banning its sale, propagation and distribution nationally. Ordinary white Zantedeschia aethiopica arum lily is not named in that Accord listing. Green Goddess is generally considered the more invasive of the two, particularly in Northland.

That said, several regional councils (Bay of Plenty among them) separately list Green Goddess as a Containment or Sustainable Options pest plant under their own regional pest management plans, so check your regional council's rules if you're dealing with the green-flowered Green Goddess form specifically. Control methods for both forms are the same: metsulfuron-methyl and glyphosate based herbicide, applied to actively growing plants, with follow-up on regrowth.

How Do I Remove Arum Lily Manually?

Digging out is a realistic option for small or scattered plants, but every piece of rhizome and root has to come out with it. Any fragment left in the ground can resprout, so this only really works at a small scale where you can get the whole root mass.

Dig around the clump and lift the full root system rather than just pulling the top growth. Bag and bin the removed material at a refuse transfer station, don't put it in green waste or home compost, since both rhizome fragments and berries can survive and re-establish elsewhere. For anything beyond a handful of scattered plants, herbicide treatment is the more realistic option.

What Products Control Arum Lily?

For most situations, a metsulfuron-methyl (MSF600) plus glyphosate mix with an organosilicone penetrant gives the most reliable knockdown, whether you're spraying whole plants or treating cut stumps. Apply to healthy, actively growing plants with good leaf area, spring through late autumn, and always plan to inspect for regrowth and treat again if needed. In wetter sites, aim for the comparatively dry late summer window so you can apply without contaminating nearby waterways.

Spray application (handgun / knapsack)

Mix MSF600 3g per 10L of water with one of the following glyphosate options, ensuring full coverage of foliage to run-off:

SuperWetter speeds uptake and cuts the rainfast period down to about 30 minutes on dry foliage, worth having in the mix given how often arum lily grows in wetter, showerier spots.

Cut stem / wipe treatment

Best treated by cutting down to the stump and pasting with Cut'n'Paste MetGel. If the stump oozes a gel-like sap after cutting, wipe this away before applying the gel so it can be properly absorbed. Cut'n'Paste Glimax Professional is a good second option where MetGel isn't on hand. If you see regrowth after treatment, add a little Cut'n'Paste Bamboo Buster or Cut'n'Paste Glimax Professional to the stump alongside the MetGel to increase its effectiveness.

Use MetGel with caution: it's ground-residual and can travel through the soil to affect the roots of neighbouring plants you want to keep, so avoid pasting stumps sitting close to desirable trees or shrubs.

Cut & spray / swab (hand-mix)

A hand-mix alternative for smaller patches, if you'd rather not use the ready-made gels. Cut off the entire plant as close to the ground as possible and immediately hand spray or swab the stump with:

Controlling Arum Lily Near Waterways

Common Mistakes

Quick Checklist

• Identify the plant: glossy arrowhead leaves, white flower with a yellow spike, growing in damp ground
• Check whether it's ordinary arum lily or the green-flowered Green Goddess form, and check your regional council's rules on the latter
• For small patches, dig out the full root mass and bin it, don't compost it
• For larger patches, spray or cut-stump treat with MSF600 and glyphosate, or paste stumps with Cut'n'Paste MetGel
• Check herbicide label restrictions before treating anything near a drain, wetland or stream
• Come back in a few weeks and treat any regrowth from rhizomes

Next step: If your patch is in or near a waterway, start with manual removal or a careful cut-stump treatment rather than an overall spray. For everything else, MSF600 3g plus glyphosate and SuperWetter per 10L of water is the most reliable combination, contact us if you'd like help choosing the right glyphosate option for your situation.

Frequently Asked Questions

What spray kills arum lily?

Our recommended mix is MSF600 3g per 10L of water, plus one of: G-360 Glyphosate 150ml, G-540 Glyphosate 100ml, or Granny Herbicide 70g, each with SuperWetter 10ml per 10L of water. Apply to healthy, actively growing plants.

Why does my arum lily keep growing back after spraying?

Arum lily survives through tough underground rhizomes. Spraying kills the visible growth, but surviving rhizome material can resprout, so most established clumps need a follow-up treatment.

Will mowing kill arum lily?

No. Mowing removes the leaves and flowers but doesn't touch the rhizomes below ground, so the plant will simply regrow.

When is the best time to spray arum lily?

Spring through late autumn, while plants are actively growing and carrying good leaf area. Avoid spraying drought-stressed, waterlogged or dying-back plants, as uptake will be poor.

Is arum lily poisonous to dogs or livestock?

Yes, all parts of the plant can irritate the mouth and throat if chewed or eaten, due to needle-like calcium oxalate crystals. Keep stock and pets away from clumps and don't leave cut material where they can get to it.

Can I spray arum lily near a drain or stream?

Only if the product label specifically allows use near water and you follow those conditions. Given how often arum lily grows right on waterway margins, manual removal or careful cut-stump treatment is often the safer choice close to water.

Further Reading

• MSF600 - the broad-spectrum metsulfuron-methyl herbicide behind most arum lily control programmes
• SuperWetter - the organosilicone penetrant that speeds uptake and shortens the rainfast window
• Cut'n'Paste MetGel - for cut-stump treatment of arum lily and other tough clump weeds