National Interest Pest Responses programme

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 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 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 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 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 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 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 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 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