Research has shown Lagarosiphon major could invade more than 90% of the country.
Landcare Research New Zealand said, in its latest bulletin, after more than 10 years since first proposing to target lagarosiphon for biocontrol, Bioeconomy Science Institute Manaaki Whenua Group was preparing to apply to the Environment Protection Agency for a release agent.
The main candidate was Hydrellia lagarosiphon, a species of leaf mining fly.
The larvae of the fly would mine the leaves of lagarosiphon, particularly the shoot tips, reducing the plant’s biomass.
Lagarosiphon is native to southern Africa and has invaded other parts of the world including Europe and Australia.
It was spread through its use as an aquarium plant.
It was discovered at the Waitaki lakes in April this year and so far could not be eradicated from those waterways.
There was ongoing work to rid Lake Wānaka of it.
It affects water flow, out-competes native plants, impacts recreational activities and the visual landscape values.
It is also a pest for hydro dams and can block power generation infrastructure.
Work to get rid of lagarosiphon was costly, labour intensive and only a short-term fix, Landcare Research said.
Biocontrol offered the potential for sustained long-term management of lagarosiphon in New Zealand with low environmental risk.
There had been three attempts to biocontrol lagarosiphon with variable success in the first two programmes. The third was still being assessed.
Research showed lagarosiphon had higher biomass and cover in New Zealand compared to its natural range in South Africa.
Other findings were consistent with the suggestion that biocontrol could be an effective tool to manage the weed.
A native aquatic moth had been found to feed on and damage the plant but there was a risk it could impact other plants if used as an agent.
The leaf mining fly’s high rate of reproduction meant it could be established well and a population sustained in most parts of the country.
Research showed female flies could lay eggs on artificial substrates if lagarosiphon was below the water, so it would be possible to establish the fly in water bodies where lagarosiphon did not reach the surface.
"All these findings provide convincing evidence that biocontrol of lagarosiphon is worth pursuing.
"We now have all the information and data required to build a strong case for release approval."
A full consultation with stakeholders and assessment of risks would have to be carried out first.
