Hunt on for invasive wild rice grass
Northlanders are being asked to keep an eye out for new patches of manchurian wild rice grass within a formal ‘‘eradication zone’’ that covers much of the region amid fears the invasive pest plant could have been spread during recent flooding.
The Northland Regional Council says in Northland, the core rice grass infestation (referred to as the ‘‘progressive containment zone’’) occurs in the Kaipara District on the banks of the Wairoa River and its tributaries, and on adjacent farmland.
Councillor Geoff Crawford, who chairs the Northland Regional Council’s biosecurity and biodiversity working party, says beyond this core area there are scattered infestations on pasture and cropping land, roadsides, and in and around creeks and farm drains.
‘‘Small infestations also occur near Whangārei, Kerikeri, Mangawhai and Mangakahia areas.’’
Crawford says because of the scale of the infestation, total eradication is not possible with current technologies, but the goal is to progressively contain manchurian wild rice to prevent spread and reduce its distribution.
‘‘Manchurian wild rice (Zizania latifolia) is a notifiable organism and is subject to a National Interest Pest Response programme administered by the Ministry for Primary Industries.’’
The programme – which has been running since 2008 – focuses control efforts on eradicating infestations outside the mapped ‘‘progressive containment zone’’ (essentially the rest of Northland).
‘‘If left unmanaged, this invasive grass represents a major threat to all river, stream and wetland systems in Taitokerau.’’
Crawford says due to the recent flooding, land in the eradication zone that hasn’t previously flooded or been exposed to rice grass may end up with rice grass clumps or rhizomes being deposited in flood debris.
It needs to be controlled as soon as possible before it spreads.
Manchurian wild rice is a giant grass that grows up to four metres high. Native to Asia, it arrived unintentionally in ship’s ballast water near Dargaville more than 100 years ago.
It has harsh, dull green leaves that are one to two centimetres wide and grow in fans.
Crawford says manchurian wild rice spreads rapidly and is extremely difficult to kill once established, so early detection of new infestations offers the best chance of eradicating it quickly.
‘‘It forms dense stands, with underlying rhizome beds that displace all other species and can alter natural water systems, causing habitat loss and increasing the risk of flooding.’’
‘‘If left unmanaged, this invasive grass represents a major threat to all river, stream and wetland systems in Taitokerau, as well as to production environments as it also readily invades pasture,’’ he says.