National Interest Pest Responses programme

Nine harmful weeds are managed under the National Interest Pest Responses (NIPR) programme. These pests could cause serious harm to New Zealand's environment and economy if they are allowed to spread. Find out more about the pest plants, what we are doing about them, and how you can help.

Pest plants managed by the NIPR programme

Some of the world's worst weeds have made their way to New Zealand. The National Interests Pest Responses (NIPR) programme is working to get rid of or control them. We work with regional councils and the Department of Conservation to stamp out these plants at more than 500 sites across New Zealand. By working together, we will be successful in protecting the mauri of our land and waterways from pests like these.

There are 9 pest plants in the NIPR programme.

  • Salvinia or kariba weed (Salvinia molesta)
  • Water hyacinth (Eichhornia crassipes or Pontederia crassipes)
  • Manchurian wild rice (Zizania latifolia)
  • Cape tulip (Moraea flaccida)
  • Pyp grass (Ehrharta villosa)
  • Phragmites (Phragmites australis)
  • Hydrilla (Hydrilla verticillata)
  • White bryony (Bryonia cretica ssp dioica)
  • Johnson grass (Sorghum halepense)

Why these plants are managed under the programme

These plants were chosen because they could have devastating impacts on our economy, environment, social, and cultural values.

For example, water hyacinth and salvinia can multiply rapidly, clogging waterways, impeding water flow, and blocking out sunlight required for healthy aquatic ecosystems. Water hyacinth is rated the world’s worst aquatic weed by the Food and Agriculture Organisation of the United Nations. It is also in the top 100 of the world’s worst invasive species across all types of plant and animal pests (Global Invasive Species Database).  

The 9 plants in the NIPR programme are hard to eradicate

The ways these plants grow and spread can make it hard to get rid of them completely.

The seeds and rhizomes (underground stems) of some of these plants can lay dormant for up to 20 years. That means we need to continue to monitor sites and look for new growth for many years after the last plant has been removed. It's only after this time we can declare it eradicated.  

Some of these plants grow in, on, or around water, on cliffs, and on remote islands. People working on the programme often need to use boats, helicopters, abseilers, sniffer dogs, and specialist equipment to access, find, and remove plants.

Water hyacinth seeds and fragments are easily spread by water, wind, and machinery. It spreads rapidly – 25 plants can form a one-hectare mat in a single growing season. Salvinia also grows fast – it can double in size in 8 days.

Banned: Water hyacinth and salvinia

Do not use them in aquariums or ponds

While water hyacinth and salvinia may look like good options for aquariums or garden ponds, they are serious pests. They are banned from sale, distribution, and propagation in New Zealand. Despite this, some people continue to illegally propagate and sell these plants or drop them in streams, ponds, and wetlands. This can undo many years of hard work to get rid of these plants.

All the plants managed under the NIPR programme are banned from sale, distribution, and propagation in New Zealand.

How you can help the NIPR programme

It takes all of us to protect what we’ve got. You can help by keeping an eye out for these 9 pest plants. These plants are all Notifiable Organisms under the Biosecurity Act 1993. If you think you see one, you must report it by calling the pest and disease hotline on freephone 0800 80 99 66.  

Read more about how to report a pest or disease

About the 9 pest plants in the NIPR programme

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Salvinia or kariba weed (Salvinia molesta)

Salvinia or kariba weed (Salvinia molesta)

Salvinia is a fast-growing, floating freshwater plant. It quickly forms large mats that can double in size within 8 days. The mats completely smother waterways and block out sunlight needed for a healthy freshwater ecosystem. As a result, oxygen levels are reduced, other aquatic plants die off, and water quality is badly affected.

The mats:

  • attract breeding mosquitos
  • block dams and irrigation systems
  • create a drowning risk for people and animals.

We are working towards eradicating salvinia from New Zealand.

Find out more about salvinia

Water hyacinth (Eichhornia crassipes or Pontederia crassipes)

Water hyacinth (Eichhornia crassipes or Pontederia crassipes)Water hyacinth (Eichhornia crassipes or Pontederia crassipes)

Water hyacinth is a fast-growing floating freshwater plant. It forms dense mats that completely smother waterways and block out sunlight needed for a healthy freshwater ecosystem. As a result, oxygen levels are reduced, other aquatic plants die off, and water quality is badly affected.

The mats:

  • attract breeding mosquitos
  • block dams and irrigation systems
  • create a drowning risk for people and animals.

We are working towards eradicating water hyacinth from New Zealand.

Find out more about water hyacinth

Water hyacinth in the news

Ugandan floating island causes national power cut – BBC News

Manchurian wild rice (Zizania latifolia)

Manchurian wild rice is a grass that forms dense stands on land and water margins. It:

  • can replace other riverbank or wetland species
  • causes silt to accumulate – altering water systems, causing flooding, and destroying habitat for aquatic plants and animals
  • displaces pasture species, reducing land productivity
  • has an extensive rhizome (underground stem) system which can damage stop banks and drainage channels.

The Manchurian wild rice programme is focused on eradication from the Auckland, Waikato, and Wellington regions. In Northland, where infestations cover about 500 hectares, the aim is to control infestations in the containment zone on the Northern Wairoa River and eliminate all other populations.

Find out more about Manchurian wild rice

Cape tulip (Moraea flaccida)

Cape tulip is extremely poisonous to humans and livestock. This small herb grows in pastures, gardens, and open areas. It produces large amounts of seed and corms (underground stems) that last a long time in the soil and are difficult to kill.

We are working towards eradicating Cape tulip from New Zealand. 

Find out more about cape tulip

Pyp grass (Ehrharta villosa)

Pyp grass is a serious threat to sand dune systems in New Zealand. It grows and matures rapidly, produces massive amounts of seeds, and outcompetes native groundcover species.

We have already eradicated pyp grass from several sites. We are working towards eradicating it from the last 2 sites in New Zealand (Blackhead and Koitiata in the North Island).

Find out more about pyp grass

Phragmites (Phragmites australis)

 

Phragmites is a grass with bamboo-like stems. It grows on water margins, forms dense stands, and crowds out native species. It can also:

  • reduce the numbers of insects and birds in wetland habitats
  • block drainage causing flooding
  • pose a fire risk when large volumes of the plant die back.

This species was once sold at nurseries and garden centres.

We are working towards eradicating Phragmites australis from New Zealand. We are controlling and monitoring sites in Hawke's Bay and Canterbury.  

Find out more about Phragmites australis

Hydrilla (Hydrilla verticillata)

Hydrilla is a freshwater plant which grows in rivers, lakes, and other waterbodies.

  • It forms large underwater colonies and shades out smaller native species.
  • Large clumps can dislodge, blocking drains and causing flooding.
  • Stem fragments easily break away and form new plants.
  • Fragments can also be spread by boats and trailers, eel nets, livestock, and diggers.

Hydrilla has been found only in 4 lakes in Hawke's Bay. No plants have been found since 2015. We rely on a fish (grass carp) to control hydrilla in these lakes. The fish were put in the lake to eat the hydrilla. They will die off naturally with the absence of hydrilla in the lakes, as they cannot reproduce in this environment.

Monitoring will continue for 15 years after the last plant is found before we can declare hydrilla eradicated from New Zealand.
 
Find out more about hydrilla

White bryony (Bryonia cretica ssp dioica)

 

White bryony is a vine which grows in a range of habitats including hedges, native forests, and paddocks. It grows rapidly, smothering low-canopy vegetation and shrubs. It also discourages native seedlings from establishing.  

We are working towards eradicating white bryony from New Zealand. It is present only in the Waikato and Rangitikei. 

Find out more about white bryony

Johnson grass (Sorghum halepense)

 

Johnson grass is considered one of the world's worst weeds. It is a summer grass that is extremely invasive and difficult to get rid of. It forms dense, spreading patches that dominates other plants, including crops. It is toxic to livestock. 

If Johnson grass was to establish in New Zealand, there would be increased labour costs to control the weed, reduced yields for most agricultural crops, and reduced net farm income.

We are working towards eradicating Johnson grass from New Zealand.

Find out more about Johnson grass

Two successful NIPR eradications

Rainbow lorikeets and hornwort have been eradicated through the NIPR programme.

We successfully got rid of wild populations of rainbow lorikeets (Trichoglossus haematodus) from New Zealand in 2014.

Hornwort (Ceratophyllum demersum) is a submerged freshwater weed. It was declared eradicated from the South Island in 2013. 

Rainbow lorikeets

Hornwort

Who to contact

If you have questions about the NIPR programme, email info@mpi.govt.nz

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