War declared on Manchurian wild rice

A $1 million-plus concerted campaign designed to halt the spread of invasive Manchurian wild rice - and then steadily reduce its impact in Northland – gets under way in earnest this month. (subs: October).

The work is being carried out by Northland Regional Council in a partnership funded by MAF Biosecurity New Zealand, which has declared the waterway-choking plant a ‘National Interest Pest’.

The programme has a budget this year of $200,000, however, MAF Biosecurity New Zealand has indicated it is likely to continue funding to fight the plant’s spread until at least 2020.

Manchurian wild rice (Zizania latifolia) is thought to have arrived in clay ballast bricks carried by timber ships and was first reported on the Northern Wairoa River bank at Aratapu in 1906.

Since then it has colonized more than 350 hectares along the river, its tributaries and side drains, also invading farm land, dams and wetlands. Small infestations of Manchurian wild rice - commonly referred to as rice grass - have also established in the Auckland, Waikato and Wellington regions, but the plant’s adaptability gives it the potential to spread throughout New Zealand.
Peter Joynt, a former Northland Regional Council Biosecurity Officer, is managing the new programme and says rice grass has the ability to seriously affect farmland crops and water bodies throughout Northland.

“It grows vigorously, blocks drains and traps sediment, reducing the width of channels and increasing flood risks. Its rhizomes spread into adjoining paddocks and form a dense mass and once established it has proven one of the most difficult plants to eradicate.“

Mr Joynt says the initial five year programme will target outlying sites in Northland to prevent further spread before pushing back into major infestations.

The work involves spraying with herbicide in spring and autumn, mostly by ground-based contractors, although helicopters may be used in some instances.

“We will be looking to co-operate closely with the co-ordinators of the local drainage districts to ensure there is minimum disruption,” Mr Joynt says.

He says the programme’s future will depend on its initial success but envisages it eventually clearing wild rice back to the Northern Wairoa River.

The initial programme involves about 140 sites and takes in Hoanga, plus properties west of Pouto Road and those north of State Highway 14 to Tangowahine, from where it includes everything north of the river. In the Kaihu Valley work will be confined to the west of SH12 up to Parore Road, above which all infestations will be targeted.

“Despite our research, we still may not know of all infested sites, so if a farmer has one out the back of their property, we really want to hear about it. Even if it turns out to be raupo (a similar-looking, non-invasive native) we would sooner check, than miss a site,” Mr Joynt says.
He says in tandem with the programme, MAF Biosecurity New Zealand is also working with the Northland Regional Council to prepare a set of national machinery hygiene protocols to prevent wild rice being transferred to new sites. Also, the National Institute of Water and Atmospheric Research (NIWA) is also carrying out an extensive study of control methods and reinstating previously infested land.

The wild rice control programme gets a thumbs-up from Kaipara District Council Drainage Co-ordinator Wayne Crump, who says wild rice is a major and costly problem in the Council’s drainage districts. “This will be a huge help and I look forward to working with the NRC team.”

Local kumara grower Andre de Bruin describes the programme as “a wonderful initiative to address the on-going invasion of rice grass in our region”.

“If we are not proactive now, imagine the problem in 50 years’ time. We owe it to future land owners.”