There are lots of names for harmful plants: pest plants, noxious weeds, pest plants, environmental weeds etc. But these all amount to the same thing; plants with harmful impact, so for simplicity we just call them weeds .

The Department of Conservation lists over 300 weeds that cause environmental damage. Regional councils and unitary authorities also have lists of weeds which are of particular concern for their areas.  There are also weed species that are banned from sale, propagation and distribution under the National Pest Plant Accord.

For more information about what makes a weed a weed, keep exploring this site or visit:

http://www.landcareresearch.co.nz/education/weeds/

• There are now more introduced plant species growing wild in NZ than native plant species. Introduced plant species continue to naturalise at an alarming rate.
• Around Auckland alone there are four garden escapes every year, adding to the more than 300 seriously invasive weeds managed by DOC.
• Only 7 species of invasive weeds have been successfully eradicated from NZ.
• Invasive weeds are one of the main threats to the survival of 61 threatened native vascular plant species; and impact on another 16 species.
• Weeds threaten the long-term survival of some native animals by changing or destroying their habitat, reducing the availability of food or breeding sites, or influencing the way native and introduced animals behave.
• Weeds are a risk to nearly 600 000 hectares of protected natural areas. Freshwater, wetlands, coastal habitats, lowland forest, shrubland and native grasslands are all particularly vulnerable areas.
• Weeds cost farmers, growers and foresters tens of millions of dollars every year in herbicides and in lost production.
• Water weeds in hydro lakes hinder electricity generation.

• Over 75% of the weeds of conservation were originally deliberately introduced to NZ as garden plants.
• Many of the 'World's Worst Weeds' are not yet present in NZ. There are over 24,700 introduced plants growing in gardens and nurseries in New Zealand; 10% of these will naturalise (establish in the wild), and 10% of these will become serious pests. 
• New weed seeds come into NZ on imported fresh fruit, used cars, used car tyres, boots, camping equipment, and in soil on and around containers.
• Humans = weed problems; and this is an international issue. People bring in new plants that escape; rubbish is dumped in bush reserves; and the expansion of coastal subdivisions and lifestyle blocks exacerbates the spread of pests.

• 10% of DOC managed land is under sustained weed management, and hundreds of thousands of hectares are threatened by weeds.
• Regional, city and district councils spend hundreds of thousands of dollars a year controlling weeds on reserves, parks and other natural areas.
• Weeds are the main threat to the existence of 61 native animal and plant species. 
• If left uncontrolled, pest problems expand exponentially. It costs $3 per hectare per year to control young wilding pines compared to $1,500 for 25 year old trees.