Pest plant pops up in pond
A pest plant previously eradicated from New Zealand was found in ponds in Tararua, but it had since been destroyed.
The Mangaone River Catchment Group, along with Horizons Regional Council biosecurity staff, recently found ponds infested with a pest water lily in the Mangaone Valley near Eketāhuna.
This was the only known location of the plant in New Zealand.
Horizons worked with the landowner to quickly remove water from the ponds where the water lily was found as a way of getting rid of it.
Horizons biodiversity, biosecurity and partnerships manager Craig Davey said fringed water lily (Nymphoides peltata) was found as part of routine water testing using the eDNA sampling method by the Mangaone River Catchment Group, who then immediately contacted the council.
“Fringed water lily forms dense mats on the surface of the water which can impede drainage, prevent stock access to drinking water, out compete native plants for habitat and disrupt recreational activities.
“The plant can reproduce via fragmentation of any root or floating stem and create new plants via creeping stems. The biggest risk though is its small bristled seeds which can be spread by people, machinery, but especially waterfowl.”
He said the plant was not a designated pest in Horizons’ pest management plan, but staff felt it was in the best interests of the community and New Zealand’s biosecurity to eradicate it.
“This plant costs millions of dollars to manage in other parts of the world where it has been introduced, so we were presented with a unique opportunity to eradicate the plant from New Zealand before it became more widespread.”
Along with an aquatic pest specialist and landowners, Horizons last month made a control plan for the site to eliminate the risk of the plant spreading.
“It was easier to take the water away from the plant than it was to take the plant away from the water, and we are confident that fringed water lily is now fully eradicated from the site.
“The last known site in the country was at Whangaparāoa, from which the lily was eradicated in the early 1990s, raising questions as to how it came to be in a stock water pond in the Mangaone Valley.”
Davey said the find was surprising, but showed the value of community groups and landowners exploring what was in their waterways and how they could work together to protect the environment.
“Work for us has now switched to finding any more sites of the plant, and we need farmers and gardeners to look in any water bodies on their properties to see what’s growing in them, and report anything questionable to Horizons.”
Native to Europe, fringed water lily is a bottom-rooted aquatic plant with long branched stems and yellow flowers with a distinct fringe around the petals.
It has floating heart-shaped leaves 10-15 cm in diameter with a scalloped margin.
To report sightings of fringed water lily or any other pest plants, call Horizons’ pest plant team on 0508 800 800.