North virtually spartina-free within six years

Biosecurity experts hope a highly invasive and environmentally destructive pest grass that until recently infested more than 100 hectares of Northland harbours and rivers will be all but wiped out within six years.

Don McKenzie, Biosecurity Team Leader for the Northland Regional Council, says the region is now several years ahead of its original target and expects to be 99 percent spartina-free by 2014, with all remaining known spartina gone by 2020.

The main spartina species in Northland, Spartina alterniflora, is a tough, salt-resistant plant that varies in height from about 0.4 to 1.5 metres and has a massive root system enabling it to form dense, choking stands in wetlands and estuaries.

Spartina was originally introduced to Northland from the United States early last century to reclaim mudflats for agriculture and it was also planted with the Government’s blessing as late as the mid-1960s to help prevent stopbank erosion.

Although the Government subsequently banned planting of spartina on tidal land in the mid-1960s, illegal plantings continued in Northland right up until the 1990s and by 2000, spartina had spread to occupy more than 100 hectares of the region’s harbours and estuaries.

Mr McKenzie says spartina is a problem because it blocks channels and harbours, accelerates siltation and causes significant habitat loss for wading birds and spawning fish as well as affecting recreational fisheries and seafood resources.

In some cases, patches of Northland spartina not contained by dense mangroves, stopbanks or tidal channels had increased in size by up to 200 times in just a decade.

By 2002 spartina had been recorded at about 150 sites in seven harbours, the Bay of Islands and the Taipa and Kawakawa rivers, with sites ranging from just a few square metres to up to 15 hectares and attempts to control it began in earnest.

 

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Mr McKenzie says since 2002, the Northland Regional Council and the Department of Conservation have between them spent more than $50,000 annually to try to wipe out the plant, efforts beginning initially in the Kaipara and then extending to rivers and Far North harbours.

He says all but a small amount of the plant is expected to be eradicated by 2014 – years ahead of the Regional Council’s original 2020 target.

Unless new sites are found, the plant is expected to have been eradicated by 2011 in the Taipa and Kawakawa Rivers, the Bay of Islands, Rangaunu, Houhora, Mangonui and Whangaroa Harbours and from the northern shores of the Kaipara Harbour by 2014.

Similarly, unless new infestations are found, all but two Parengarenga Harbour sites are expected to be free of spartina by 2012, with all but one Hokianga Harbour infestation eradicated by 2014.

However, Mr McKenzie says sites will need to be checked for at least five years after the plant is thought to have been wiped out to ensure nothing has been missed.

He says the public will have a vital role to play in that regard and urges anyone noticing a grass they do not recognise growing on a mudflat to immediately contact the Council – or take a sample of it into their local Regional Council office for identification.

Mr McKenzie says while ground-based methods can be used for initial control of smaller spartina sites, aerial spraying with the herbicide Gallant is the only practical and cost-effective method for initial control at most large sites due to their location and accessibility issues.

“Aerial spraying is required for three years after which the infestation has typically been reduced to a size that can be successfully controlled from the ground instead.”