Do you remember seeing photos of brides from the 1930s each clutching a huge and unwieldy spray of what are commonly called arum lilies? They grew so well in New Zealand that they could be found in most gardens some years ago.
But like so many introduced plants from other parts of the world moderation was left behind in the host country, and they took off here like weeds in any damp places they could find, including pasture, particularly in the northern North Island.
The most well known version is Zantedeschia aethiopica which is neither a true arum nor a lily. Named after an early Italian botanist, it came here from South Africa. Growing to around a metre in height, it forms clumps which spread themselves across swampy pasture and wasteland. The well known white ‘flower’ with spiky yellow centre is actually a white ‘bract’ and the central spike is the real flower, which has its male parts at the top and female ones at the base. The leaves are large and arrow shaped with long stems, and the roots are tuberous, white and fleshy. The berries are green or yellow, up to 10mm across in a spike formation. The white bract turns green after flowering and covers the ripening berries, rotting away when they are ripe.
Much of its wide dispersal has been in garden waste. Methods of disposal recommended are to slash stems and dig out rhizomes. Stems and leaves may then be left to mulch, but rhizomes should be dried and burned, or wrapped in plastic bags before being sent to landfill, as otherwise they will grow again from any part.
Eradication needs to be systematic, and both metsulfuron and glyphosphate will work, if used with a good penetrant to ensure good coverage and absorption.
A much lower growing arum which is even more insidious in the way it can spread is Arum italicum or Italian arum. This one is often found spread from old gardens. The leaves can be up to 30cm long but stalks are only 20-40cm. Leaves are glossy and dark green, with a creamy mid-rib and main veins, giving them a lacy look. The ‘flower’ bract is translucent, greenish white, and grows vertical, cupped round the spadix or flower spike, and the flowers appear from October-November. If the flowers are not picked the seed heads form on the stalk after the flower dies back, and are around 1cm across and bright orange, which makes them tempting for children.
Found in damp localities throughout the North Island, Italian arum can also be found in Nelson, Marlborough and Canterbury.
The roots form a main tuber about 4cm in diameter, but the plant also produces many small tubers which make it very hard to eradicate, as any left behind when dug up will sprout again.
Despite all my efforts to get rid of Italian arum it continues to flourish in my garden and paddocks, both on earlier treated sites and also in new ones. It tends to appear under established shrubs, along fencelines and under pasture hedges, with new clumps found further out into the neighbouring paddock. I have tried spraying with Roundup (admittedly without using a penetrant) and mowing and cutting and pulling. A comment site found on Google showed that there are a variety of views on when to apply spray and whether the plants should be slashed first. But there seemed to be general agreement that in wet conditions it was extremely difficult to eradicate. I try to ensure I pick every flower when they appear, and therefore I’m not finding seed heads, so I am not sure how it spreads out into paddocks.
Animals avoid it and, like all ‘arums’ all parts of the plant are poisonous. If you find it on your land you may have a long job to get rid of it.