Weed control in forestry

Weeds are plants that are growing well where they are not wanted. You need to monitor your forest so you can find and deal with invasive weeds before they become a problem.

Control weeds

Controlling weeds is an important part of looking after your forest. Invasive weeds can:

  • steal nutrients needed by trees
  • restrict the growth of saplings
  • harbour pests that may be harmful to your trees.

Regular inspections are the best way to find and deal with invasive weeds before they become a problem.

The Department of Conservation has a guide on how to control weeds.

Wilding conifers

Conifers are trees which spread from cones, such as pine trees. A wilding conifer is an unwanted conifer that has spread naturally, instead of being planted by foresters. Wilding conifers have become a threat to New Zealand's native landscape, high country farming and biodiversity.


Gorse is a scrub weed, originally introduced as a form of farm hedging. It is easily distinguished from other pest plants by its thorny leaves and bright yellow flowers.

Gorse can spread quickly over large distances. The seeds disperse explosively, spreading across many metres. They can also be picked up by the wind and by the fur or fleece of passing animals.

Gorse grows quickly and densely and can outcompete pasture and forestry for nutrients, water, light and space. It can regrow quickly from any remains left after burning or cutting, making it hard to control and even harder to eliminate. Biological methods (animals and insects) seem to be the most effective control methods.

Gorse plants dry out over summer, increasing the risk of fires. 

Exotic plants

Smothering vines can affect forest canopies. These include banana passionfruit, bomarea, Chilean flame creeper, climbing spindleberry, ivy, Japanese honeysuckle, old man's beard, mothplant and wonga wonga vine. The New Zealand Plant Conservation Network and Weedbusters can help you identify these.

Insects can be used to control weeds

Some insects can be used to control invasive weeds. Manaaki Whenua has a good guide to collecting and distributing insects as control agents for a range of weeds, including:

  • broom
  • gorse
  • hawkweeds
  • Japanese honeysuckle
  • lantana
  • mist flower
  • old man's beard
  • Tradescantia.

A list of Manaaki Whenua's current biocontrol projects can be found on its website.

Regional pest management plans

Many regional and district councils require landowners to manage and control certain pests, weeds and diseases. Check with your council to find out what responsibilities you may have.

Monitoring pests, weeds and diseases

Tell the Ministry for Primary Industries if you see anything unusual.