Manchurian wild rice a real pest

Manchurian wild rice in Waikanae.

A recent survey of the Harakeke wetland has shown the battle against the invasive spread of Manchurian wild rice is being won, but if left unchecked will spread, crowd out native plant species and clog waterways.

"It may sound pretty cool, like an exotic ingredient in MasterChef, but nothing could be further from the truth," Greater Wellington Regional Council pest plants adviser Kieran McLean said.

"It's a real pest capable of doing damage to our environment, and it's our job to control its spread."

The highly invasive, giant, semi-aquatic plant displaces native plants from our waterways, out-competing them for light, nutrients and space, and contributes to sediment build up that can lead to flooding.

Leave it be and the plant, otherwise known as Manchurian rice grass (Zizania latifolia), will choke our waterways, force native plants out and undermine habitat values.

"So far, it's contained within Te Harakeke Wetland and Pharazyn Reserve in Waikanae but stopping its spread isn't easy.

"Each year at this time we survey both areas to gauge its presence before running annual control operations.

"It's hard to find and difficult to kill but we're making progress and our goal of total eradication is realistic.

"But it will take time.

"We believe the area infested by Manchurian wild rice is reducing, though it's hard to assess and we have to keep returning to make sure it's gone from the areas we've cleaned.

"That's why we need annual assessment of its spread."

Because of the plant's potential impact it has been recognised by the Ministry for Primary Industries as a 'National Interest Pest Response' species, to be contained within the Kaipara district [north of Auckland] and eradicate everywhere else in New Zealand.

"Our job is to eradicate the plant in our region, which we do through ground and aerial spraying on wetland which is often inaccessible by foot.

"Growing to around 4 metres in salt or fresh water, it looks very similar to raupo though it has a stout midrib and its straight leaf tip.

"It grows in streams, pasture, drains, ponds, wetlands and lake margins."

Mr McLean said if Manchurian wild rice is suspected, people should contact their council.
"Its biosecurity experts will identify the plant and if it is Manchurian wild rice, they will control it for free and record the location for future work."