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Pest plant stirs up strife

The loosestrife plant may be a pretty purple hue, but the Department of Conservation [DOC] warns that the invasive weed could pose a dangerous threat to Wairarapa’s environment.

DOC Wairarapa has been treating purple loosestrife in Boggy Pond for the past few years, but recently it’s also been spotted in Wario Lagoon.

A DOC spokesperson said that, as an aggressive invader of wetlands, if the loosestrife reaches Lake Wairarapa it could settle in less accessible places, making its spread very hard to control.

“Additionally, Lake Wairarapa and Ōnoke Spit collectively have a very long shoreline,” the spokesperson said.

“If purple loosestrife was to take hold it would change shoreline habitats where there are threatened species.”

The lake and its surrounding wetlands are home to 96 bird species, including the critically endangered Australasian bittern, and 25 native fish species.

Many of these species rely on a constant and specific habitat to survive, the spokesperson said: “Kākahi, shore birds, and native turf plants all need an open shoreline.”

Each loosestrife plant produces millions of long lived, highly variable seeds from an early age.

Seeds can float around in water and then take root as soon as water levels go down, something the spokesperson noted benefits the plant’s spread.

“When you have widely fluctuating water levels, such as there is in the lagoons that surround Lake Wairarapa, the seed will exploit that.”

While loosestrife has not caused major issues in Wairarapa before, there are other areas in New Zealand where it has created havoc, such as Horowhenua.

It’s also a big problem overseas in places like North America.

When it comes to controlling the plant, the spokesperson said DOC has undertaken canoe-based and ground-based herbicide control.

“Last year we were able to undertake a helicopter survey that identified 15 plants that were later treated from the ground,” the spokesperson said.

“This year we are planning to remove the flowers before treating each plant with herbicide, as there is evidence that seed is less likely to survive if the flowers are removed first.

“It’s also better for our native bees, which are attracted to the flowers. Hand pulling purple loosestrife is not effective.”

While it’s not believed that loosestrife has spread to Lake Wairarapa yet, there is a risk it may have travelled, so the spokesperson is urging users of the lake to keep an eye out for it.

If anyone sees it, they can report it to [email protected]

Bella Cleary
Bella Cleary
Bella Cleary is a reporter at the Wairarapa Times-Age, originally hailing from Wellington. She is interested in social issues and writes about the local arts and culture scene.

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