Pest plant control methods

Ways to control smaller and accessible infestations of pest plants:

• Hand weeding– remove plants from the site to avoid fragments or seed colonising.
• Ringbarking – strip bark around the entire circumference of a branch or trunk of a woody plant.
• Mechanical weeding– with weed eaters or rotary slashers.
• Controlled grazing– where the weeds are palatable to grazing animals.
• Spraying or chemical weeding– spray on the leaves and/or stems of targeted plants.
• Stump treat–woody plants can be cut near the base of the trunk, and herbicide gel or concentrated herbicide can be applied.
• Drill and Fill – drill angled holes into the stem of woody weeds (down to the sapwood), then fill the holes with herbicide.

If the infestation is over a large area, where other methods are not effective, these control methods are some of the best options:

• Aerial spraying– used to tackle large scale infestations of gorse or blackberry, for example, where they are unable to be effectively controlled using ground-based methods. In most cases the herbicides used are the same as those available at most garden centres. Find out more about aerial spraying.
• Check, Clean, Dry – Freshwater pest species can move between waterways through human activity. Once established, they can squeeze the life out of our country’s most precious rivers and lakes. Find out more about Check, clean, dry.
• Biological control– a long-term approach to widespread pest control which involves introducing a natural enemy to help control the plant. Manaaki Whenua Landcare Research undertakes the research, strict testing procedures and trialling to ensure that any new organism will only attack the pest plant and no other plant species.

Greater Wellington contributes towards the National Biocontrol Collective which includes the majority of regional councils, DOC and several district councils. Find out more about Biological control.

• Research first – find out about the weeds you’re dealing with first and if necessary, ask for expert help.
• Start small – avoid creating large cleared areas which can allow new and different weeds to establish.
• Work in stages – tackle outlying weed patches first to slow the rate of weed spread before starting on the worst areas.
• Keep safe – Always follow the safety precautions of any herbicide carefully.
• Good timing – destroy weeds before they fruit or seed to prevent a new generation of weeds.
• Don’t spread them – when shifting dead weeds take care not to spread any seeds or fragments around that could grow again.
• Smart disposal – decide on the best disposal method to use before you start, particularly if working in a large area

1. Research first - find out about the weeds you're dealing with first and ask for expert help.
2. Start small - avoid creating large cleared areas which can allow new and different weeds to establish.
3. Work in stages - tackle outlying weed patches first to slow the rate of weed spread before starting on the worst areas.
4. Keep safe - if using herbicides, contact a local Weedbusters group for advice.
5. Good timing - destroy weeds before they fruit or seed to prevent a new generation of weeds
6. Don't spread them - when shifting dead weeds take care not to spread any seeds or fragments around that could grow again.
7. Smart disposal - decide on the best disposal method to use before you start, particularly if working in a large area

• Ringbarking or girdling - strip bark around the entire circumference of a branch or trunk of a woody plant
• Mechanical weeding - with weed eaters or rotary slashers
• Controlled grazing - where the weeds are palatable to grazing animals
• Spraying or chemical weeding - spray on the leaves of targeted plants
• Stump treat - if the weed is particularly woody then cut near the base of the trunk and apply herbicide gel or concentrated herbicide
• Check, Clean, Dry your gear - to control the spread of aquatic weeds between waterways

• Replace bad with good - plant natives or non-weedy plants as you go. Download this free Plant me instead booklet and check out our native plant guide:

Native Plant Guide

This guide explains how you can use native plants to help our native ecosystems survive and flourish, and at the same time beautify your garden or your rural property. For… Read more here

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• Help native seedlings - provide shelter and control animal pests
• Mulch - this discourages weeds and helps good plants grow
• Regular attention - ongoing control of weeds keeps maintenance at a manageable level. Use selective herbicides so non-weedy plants survive and follow the directions closely.

The best follow-up method can depend on the environment you are working in. Contact Department of Conservation or local Weedbuster group if you need further advice.

Biological control is a long-term approach to pest control which involves introducing a natural enemy to help control the plant. 

Manaaki Whenua Landcare Research undertakes the research, strict testing procedures and trialling to ensure that any new organism will only attack the pest plant and no other plant species. 

Greater Wellington contributes towards the biological control collective which includes the majority of regional councils, DOC and several district councils. Greater Wellington biosecurity officers currently release biocontrol agents in the Wellington region. When agent populations are high enough, they may distribute them on to new sites.

Biocontrol agents released in the Wellington Region

Biocontrol agents are currently being researched for a wide range of common pest plants including banana passionfruit, wild ginger, Japanese honeysuckle and Darwin's barberry.

Aerial spraying is used to tackle large scale infestations where they are unable to be effectively controlled using ground based methods.

The main pest plants controlled by aerial spraying are gorse or blackberry.

In most cases the herbicides used are the same as those available at most garden centres.

Find out more about safe spraying programmes