Northland battles Manchurian wild rice
Wild rice dominating the margins
of Phoebies Lake. Images courtesy
of Northland Regional Council.
Northland's efforts to tackle a weed that hitchhiked its way into the region more than a century ago – hidden among clay ballast bricks in timber ships – have been given a welcome boost thanks to MAF Biosecurity New Zealand (MAFBNZ).
Manchurian wild rice is among Northland's worst pest plants; its spread is seemingly relentless, it loves damp feet and sets like concrete!
However, Northland Regional Council Chairman Mark Farnsworth says the region's battle against rice grass has been enhanced by MAFBNZ's decision to make the weed a national interest pest.
Mr Farnsworth says Northland appreciates that wild rice could become a real problem for other regions if its spread is not contained. It is currently largely restricted within the region's Kaipara district, including the Dargaville area, although smaller sites are also known in the Whangarei and Far North Districts.
“I believe the tide is turning on this plant and we look forward over the coming years to a strong partnership with MAFBNZ. We have a partnership plan which will see large areas of wild rice under management and new methods of control developed as a result of research.”
“We will be meeting with local Kaipara councillors and liaising with other stakeholders such as iwi and community groups as the work gets underway – it will mean increased activity on the ground to spray wild rice and follow up over several years to ensure eradication.”
Mr Farnsworth says wild rice has a long history in Northland and was first identified growing on the banks of the Kaipara's Northern Wairoa River at Aratapu in 1906.
“Timber ships carrying clay ballast bricks which contained its seed were thought to have transported the species from its natural range in eastern Asia to New Zealand. Bricks containing the seed were unloaded onto the river banks as kauri timber was taken aboard, and the plant took hold.”
Mr Farnsworth says since its introduction more than a century ago, wild rice has colonised more than 350 hectares of the Northland region along 55 kilometres of the Northern Wairoa River – from Tokatoka in the south, to Kirikopuni in the north. It has grown up the main tributaries but also into many drains, invading large areas of low-lying farms, dams and wetlands.
“Wild rice is an extremely hardy plant with an ability to grow successfully over a wide range of temperatures, soils, as well as saline and freshwater environments. Once established, it has proven one of the most difficult to eradicate as it will grow and survive from the small fragments of rhizome.”
Mr Farnsworth says wild rice's move out of the Kaipara and into wetlands and drains in the Whangarei and Far North Districts is attributed to machinery moving between the areas. It has the ability to seriously affect Northland's farmland, crops and water bodies because of its vigorous growth and ability to form dense stands, which rapidly block drains and alter water flows.
“Drainage systems, canals, floodgates and associated riverworks in the heavily infested Northern Wairoa area have been completely blocked; particularly where the channel width and rate of water flow is insufficient to prevent the weed spreading bank to bank.”
He says Manchurian wild rice traps sediment moving in the channels and the capacity of the channel is rapidly reduced, increasing the risk of flooding.
Rhizomes also spread out into adjoining paddocks and form such a dense mass underground that the soil becomes compacted and drainage is impeded.
“The rhizome system can also grow into river stopbanks, causing slumping during winter which requires maintenance and additional drainage.”
Wild rice's ability to totally suppress all other species, degrade stopbanks and readily colonise pasture and crops means lost farm productivity and ongoing control costs.
Herbicide can be applied using helicopters or gun and hose, however, stands of mature wild rice are tall and dense often making access difficult and reducing the penetration effect of the spray. Tracks are sometimes pushed through the larger stands using a tractor to open them up and create better access for spraying.
Mr Farnsworth says Manchurian wild rice is also extremely invasive in native vegetation, displacing raupo, reducing plant diversity and, in the long term, excluding all other species.
The plant detracts from the scenic and recreational value of waterways, restricting boating and fishing. Obstruction of vision on road margins and invasion of roadside water tables is an additional problem, and Māori cultural values are impacted upon where traditional gathering areas for harakeke, kuta, raupo or kai are degraded.
Meanwhile, despite the formidable nature of its plant foe, Mr Farnsworth says the Northland Regional Council is optimistic Manchurian wild rice can be controlled, and even eradicated from some areas.
“We have had good advice from MAFBNZ officials on their expectations of containment and we have been controlling a number of infestations for several years now. We know that containment – and even eradication in some cases – is achievable.”
- Don McKenzie, Biosecurity Team Leader, Northland Regional Council
- Enquiries regarding MAFBNZ's Manchurian wild rice programme should be directed to Victoria Lamb, Senior Adviser Pest Management, victoria.lamb@maf.govt.nz.
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Page last updated: 12 June 2008