Northland weed-busters tackling rampant moth plant at Onerahi

Chrissie Stephenson discovered the Moth Plant in her own backyard before noticing it on the roadside in Onerahi. Photo / Tania Whyte

A group of Onerahi residents are tackling a picturesque rampant noxious weed that has the ability to take out mature, native trees.

Moth plant, with the botanical name Araujia hortorum, is believably named because butterflies, moths and bees are attracted to its flowers where they can become trapped. It is also known as kapok vine, mothvine, cruel plant, milkvine and milk weed.

It is an evergreen leafy vine which can grow up to 8m high, with clusters of small creamy-coloured tubular flowers that are sometimes tinged with pink and are followed by large seed pods, similar looking to the vegetable choko.

The pods release 250-1000 parachute-like seeds per pod which can be dispersed 30km away by wind or spread on clothing or by animals.

The seeds are poisonous and stems contain a milky sap which can irritate people's skin and eyes. It is thought to have originated in Brazil where they were a garden-scape plant before being introduced to New Zealand in the 1880s as a pretty garden creeper.

The Moth Plant is often left to expand in peoples' gardens as it is picturesque. Photo / Tania Whyte

According to Onerahi resident and moth plant buster, Chrissie Stephenson, because many believe it to be a pretty feature to their garden, they leave the vine to grow and take over.

"It's a pest that has escaped and is infectious like a disease. It's growing rampant in our environment and, with just a bit of action, we can do something about it," she said.

"It has seed pods that look like chokos and people think, 'Oh, it's a choko', but the pod bursts open in the summer and throws out feather-light seeds that, with the right wind, can carry across to islands."

Moth plant seed has made its way from the mainland to the Hen and Chicken and Poor Knights Islands. Matakohe-Limestone Island rangers and volunteers have also been battling the weed for years.

Stephenson became aware of the weed four years ago growing in her own backyard.

"I was just about to head off on holiday when I found one in the kowhai tree next to my house. I looked it up and realised what it was so delayed the departure of my holiday to get it down and was just astounded how the creeper had extended itself and got right up my kowhai tree."

After that, she started noticing them on her journeys and, after seeing success from nearby Weed Action Whangārei Heads, she formed a small group in her neighbourhood to try and eradicate the weed closer to home.

They began by tackling the seed pods. However, this summer, while the plants are flowering and visible, they are addressing the problem at the roots.

Chrissie Stephenson and a small group of Onerahi residents are tackling the rampant plant themselves. Photo / Tania Whyte

"We've done a lot of work removing the pods but the vine is still going to come back next year and we can't keep up with the number of pods," said Chrissie. "So this year we are focusing on cutting the vine base at ground level and painting it with poison which is not cheap."

Accessing the base usually involves crawling around hedges and bushes – no easy feat for the group who are, all but one, aged 70-plus. They are hoping to accrue younger people to help with their mission and gain funding assistance to cover the cost of the poison and disposal.

She believes they have eliminated a significant amount of moth plant over the last three years - from one property they gathered around eight bags of pods - and are seeing results with less around.

Stephenson said the invasive weed has the ability to bring down a pōhutukawa tree and she recently saved one when she discovered a moth plant growing behind it.

"It creeps up over bushes and one vine will snake its way up through a tree and, at the top, the sun will ripen the pods, which will burst and the seeds will fall to the ground and more vines will grow, eventually covering the canopy and smothering the tree. It's got its survival instincts very sorted.

"The government is funding pest control, which is great, but how about investing in the environment where our birds live. As well, volunteers and DoC staff have to go to the islands to control moth plant when it should be controlled here on the mainland."

Northland Regional Council (NRC) biosecurity manager for weeds and freshwater Joanna Barr said moth plant was too widespread around Whangārei and the region to be listed as one of NRC's eradication species. Instead, NRC offered a supportive role in its eradication.

"We try to support landowners and community groups in their own efforts.

"We would never have enough staff or contractors to chase down all those pods but if people deal to them on their own property, collectively it could make a bigger impact. What we can do it try to support landowners and community groups in their efforts and raise awareness."

She said NRC was trialling targeted awareness to three key project areas – Whangārei Heads, Brynderwyn and Tutukaka Coast – with roadside signs, Facebook posts and disposal areas.

While an online biofund application was available for larger projects, property owners were welcome to contact NRC for advice on how to eradicate the weed.

Barr said the most effective and easiest method was to cut and treat the plant at the base in January while flowering.