Manchurian wild rice programme making inroads

Almost three years into a major $1 million-plus campaign to tackle one of Northland’s worst pest plants, organisers believe they are beginning to turn the tide in a lengthy war on Manchurian wild rice.

The campaign – designed to halt the plant’s spread then steadily reduce its impact in Northland – is being carried out by the Northland Regional Council in a partnership funded by MAF.

MAF has declared the waterway-choking plant a ‘National Interest Pest’. Manchurian wild rice forms dense, long-lived stands on land and water margins, blocking out other riparian species. It also blocks drains and destabilises stopbanks, causing flooding and invades flood-prone pastures and wetlands.

Peter Joynt, a former Northland Regional Council Biosecurity Officer who is managing the regional programme, says he is pleased with progress to date.

“With the completion of the third year approaching, we now have more than 300 individual sites covering approximately 90 hectares included in the programme.”

Mr Joynt says the campaign currently has an annual budget of $300,000 and targets all sites of Manchurian wild rice throughout Northland. However, most work is carried out in the Kaipara district, where the heaviest infestations occur.

He says while the battle against Manchurian wild rice is expected to be a long one - with MAF indicating it is likely to continue until at least 2020 – the tide is beginning to turn in favour of those working to control it.

“The early years of the programme targeted outlying sites first, to prevent further spread, before pushing into more heavily infested areas alongside the main rivers, streams and drainage canals and we’re now starting to make real progress.”

Mr Joynt says the work involves spraying with herbicide in spring and autumn, mostly by ground-based contractors, with helicopters used where access is difficult.

Four contractors who undertook control work during previous years have been re-engaged and treated a large number of new sites, as well as carrying out follow-up spraying at all previously treated sites. (Once a site is included in the programme ongoing follow-up treatment is required for several years to ensure complete eradication.)

Mr Joynt says work has now progressed to the point where the programme can turn its attention to some of the more heavily-infested areas.

“Control work so far this financial year has included more than1000 hours of contract labour and seen many thousands of litres of herbicide applied.”

He says aerial spraying of sites on the Maunganui and Kaihu Rivers, which are inaccessible to ground-based machines, continues to make inroads with these infestations.

“Meanwhile in addition to the works budget, MAF has provided $20,000 annually in the last two years to fund trials of various herbicides and application rates at the Northland Research Farm at Dargaville.

“Trials - designed and monitored by NIWA scientist Paul Champion - are also underway on the Tangowahine Stream. These aim to revegetate river and stream banks following the removal of Manchurian wild rice infestations.”

Mr Joynt says a great deal of work has already been done to locate and identify Manchurian wild rice infestations and the Northland Regional Council is still keen to record any other outlying sites so these can also be included in the programme.

Because Manchurian wild rice and native raupo grow in similar areas and conditions, they can sometimes be confused by landowners.

“If you think you may have a Manchurian wild rice infestation on your property, especially in old dams or swampy areas, it’s better for us to positively identify the species. Don’t hesitate to get in touch with your local regional council office as we can help positively identify which species it is.”