Good Progress in Manchurian Wild Rice Programme

A major $1 million-plus campaign designed to halt the spread of the invasive Manchurian wild rice plant - and then steadily reduce its impact on Northland - is progressing well.

Manchurian wild rice forms dense long-lived stands on land and water margins, blocking out other riparian species. It blocks drains and destabilises stopbanks, promoting flooding, and also invades flood-prone pastures and wetlands.

Now in its second year, the campaign is being carried out by the Northland Regional Council in a partnership funded by MAF Biosecurity New Zealand (MAFBNZ), which has declared the waterway-choking plant a ‘National Interest Pest’.

The programme, which targets infestations of the plant in the Kaipara District, has a budget this year in excess of $200,000. There are now almost 160 sites covering about 70 hectares which are being actively managed.

Programme Manager Peter Joynt, a former Northland Regional Council Biosecurity Officer, says he is pleased with progress to date.

”The programme is initially targeting outlying sites to try to prevent the pest from spreading its reach even further, however, the focus will eventually shift back into existing major infestations in and around the district’s rivers and streams.

“While MAFBNZ’s current funding agreement with Northland Regional Council is for a five-year period, the response will continue to fight the plant’s spread until at least 2020.”

The current programme involves spraying infested sites with herbicide in spring and autumn, mostly by ground-based contractors, although helicopters are also sometimes used.

Control work so far this financial year had included almost 300 hours of contract labour, including follow up spraying on more than 140 sites treated the previous year.

Mr Joynt says spring monitoring revealed extensive dieback and ‘brown out’ of the treated vegetation, with approximately 10 to 20 percent of sparse regrowth occurring.

Similarly, aerial spraying of sites on the Manganui River in April and October last year had also resulted in excellent brown out and dieback of all scattered infestations.

He says several large and extensive sites in the wider Dargaville area are also being prepared for aerial spraying next month.

“As these sites are near cropping and other sensitive areas, a ‘buffer strip’ has been sprayed from ground-based machines to help ensure only target plants are treated.

Mr Joynt says the sites all contain particularly difficult management conditions, including old river bed loops and waste areas with mud springs.

He says reducing and managing these infestations effectively will take considerable time and resources.

Extremes of Northland weather in recent months had also hindered planned trials of slashing, crushing and burning wild rice at the Northland Research Farm at Dargaville.

“The slashing and crushing work had had to be postponed due to an extremely wet spring that had made conditions dangerous for heavy machinery to work in, while the drought currently affecting Northland means nothing can be burned due to fire bans,” says Mr Joynt.

Mr Joynt says while the trials have been postponed until the fire bans are lifted, ongoing attempts to locate “outlier” infestations of wild rice are continuing.

He says it’s important to locate such infestations – usually in an old dam or swampy area - so that they can be included in the control programme.

“As Manchurian wild rice and the native raupo are often confused we suggest people who suspect they may have this pest plant tucked away on their property somewhere contact the Northland Regional Council so it can be positively identified.”

Mr Joynt says as resources become available, officials hope to eventually rid Kaipara of outlier Manchurian wild rice infestations so they can concentrate on the traditionally heavily-infested areas in and around Kaipara’s rivers and streams.

ENDS

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