Working together to protect New Zealand

Weed Information

What are Weeds?

Weedbusters isn't about the 'nuisance' weeds that pop up in your vege patch or flower garden - these are annoying, but tend to be a problem only in areas under cultivation.  

Weedbusters is about the invasive plants which have a harmful impact on the wider natural environment, on our economy, and on human and animal health.  

There are a lot of different terms used for these plants by different organisations for different reasons.  The Department of Conservation lists over 300 'environmental weeds' that threaten the ecosystems they are looking after. Regional councils and unitary authorities also have lists of 'pest plants' (or 'plant pests') which are of particular concern for their areas.  There are also 'NPPA species' that are banned from sale, propagation and distribution under the National Pest Plant Accord.

But there are also other invasive plant species that, for one reason or another, aren't on these lists, but are still of concern because of their weedy growth habits.  So, for simplicity's sake, we refer to ALL invasive plant species as 'weeds'.   

Why worry about 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.

  • Only a handful of invasive weed species have ever been successfully eradicated from NZ - once weeds get a foothold here, they are very expensive and difficult to get rid of.
  • 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.

How weeds are introduced

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. 
  • While there is always a risk of new weeds getting past our stringent border controls, most of the weeds of the future are already here, and many are already showing weedy tendencies.
  • There are over 24,000 introduced plants growing in gardens and nurseries in New Zealand; a rough rule of thumb is that 10% of these will naturalise (establish in the wild), and 10% of these will become serious pests. 

Most of the spread of weeds in New Zealand is because of people.

  • 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.

What weeds cost

If left uncontrolled, weed problems expand exponentially - and so does the cost of dealing with them.

  • Regional, city and district councils spend hundreds of thousands of dollars a year controlling weeds on reserves, parks and other natural areas. The Department of Conservation spends millions. 
  • Farmers, growers and landowners have to budget large amounts to control weeds on their properties to safeguard their industry. 
  • And volunteers spend untold hours around New Zealand busting weeds to protect their precious local natural areas.