Eco-sanctuary island in Whangārei Harbour at risk of pest invasion

One of Northland's three containment zones, where Lantana Camara is rampant. Photos / supplied

A biosecurity watchdog says an infestation of one of the world’s most invasive weeds at Onerahi could spread to an eco-sanctuary island in nearby Whangārei Harbour.

The outcrop of Lantana camara – an aggressive and soil-poisoning weed – is on a bank at 270 Beach Rd. There are fears it could potentially spread to nearby Matakohe-Limestone Island. It was reported in late October to Northland Regional Council (NRC) by one of its councillors Jack Craw who chairs the council’s biosecurity and biodiversity working party.

Local weed buster groups had also spotted the outcrop but said it was too big a challenge for them. They were pleased NRC had told Whangārei District Council (WDC) to get rid of the weed, which has been scheduled for spraying (weather permitting) on December 9.

Lantana is a problem plant worldwide. It was introduced to New Zealand from tropical South America as an ornamental garden shrub. It is a serious problem in Northland and Auckland, where it forms dense thickets that invade and smother a wide variety of areas from native and exotic forests to domestic gardens, islands, cliffs, foreshores, roadside, sand dunes, quarries, and wasteland.

Whangārei District Council will be spraying this outcrop of Lantana at Beach Rd, Onerahi, amid fears it could spread to nearby Matakohe-Limestone Island. Photo / supplied

The NRC’s biosecurity manager for pest plants Joanna Barr said Lantana camara was so invasive in parts of Northland that the plant was included in the NRC Pest and Marine Pathways Plan (2017-2027) as a “progressive containment” weed. That category is for areas of weeds that were already well established and could not be eradicated short-term but could be reduced over time and the spread into uninfested areas lessened or stopped.

Northland currently had three containment areas of Lantana camara: Rangaunu, Whangaroa, and Hokianga, Barr said. Anyone who saw or suspected it outside of those mapped containment zones should report it to NRC immediately.

“We have two rules in the plan relating to Lantana; for infestations on small properties (less than 0.5ha) landowners are required to control all Lantana. For larger properties/infestations we assist land occupiers to develop a management plan to reduce the risk of spread.

“Being bird dispersed, it is an extremely difficult weed to contain so the programme’s focus is on slowing spread and reducing the impacts,” Barr said.

A low, scrambling, shrub, Lantana has thorny stems and a strongly herbaceous smell. It blooms year-round with clusters of brightly coloured flowers, which turn into berry-like fruits that birds eat and then disperse the seed. The plant also spreads via suckering roots, which can be spread in contaminated soil and dumped vegetation.

Lantana camara can be poisonous to people and grazing stock. Ingesting the flowers, fruits, and leaves can cause vomiting, diarrhoea, difficulty breathing, and liver failure. The leaves also cause contact dermatitis.

The plant can thrive in all soil types and growing conditions including drought, shade, and fire, which gives it a competitive advantage over native species. It is also allelopathic in that it produces a toxin that poisons the soil around it so other species can’t survive.

As it is listed on the country’s National Pest Plant Accord, it is an offence under the Biosecurity Act 1993 to breed, distribute, release, or sell the weed anywhere in New Zealand. Existing plants must be destroyed.

Barr said all cultivars of Lantana camara are banned from sale in New Zealand. The flowers of those variants varied in colour but were mostly a combination of pink and creamy to bright yellow, but can also be orangey-red tones. There was a similar species Lantana montevidensis, which had purple or white flowers, that did not seem as invasive, and that species was permitted to be sold.

Three parts of Northland are heavily infested with Lantana Camara. NZ Herald Graphic.

The NRC and New Zealand Weedbuster websites advise similar methods for getting rid of Lantana camara, saying it can be sprayed with glyphosate, best done during November and December. The weed could also be cut down and its stumps painted with glyphosate or dug out, although that was not generally recommended as any remaining root fragments could resprout. Another non-chemical method to destroy the plant was to cut it off at ground level and cover the stump until it rotted with thick black plastic. The removed plant material should either be left on site to rot or dried thoroughly then compost or burnt.

Barr said WDC had also previously been asked by NRC to deal with infestations on Boswells track, Onerahi, along the Waipū Cove walkway, and at Puke Kopipi in Ngunguru. NRC was currently in discussion with the Far North District Council about infestations at Coopers Beach, Kerikeri and Pukenui.

In 2012, NRC spearheaded the release by the Environmental Protection Authority of two rust fungi – Puccinia lantanae and Prospodium tuberculatum – as biological warfare against Lantana. Both fungi were released in Whangaroa, Doubtless Bay, Awanui and Kohukohu, during 2015.

The leaf rust Prospodium tuberculatum had some impact on vigour and seed production, but not enough to provide substantial control of the plant at this stage, Barr said.

Sarah Curtis is a news reporter for the Northern Advocate, focusing on a wide range of issues. She has nearly 20 years’ experience in journalism, much of which she spent court reporting. She is passionate about covering stories that make a difference.