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How to control the invaders - Weed and Pest Control

Most of us will have seen possums, rats and other rodents scurrying around and weeds growing up native trees. Goats, pigs, stoats and hedgehogs also have a huge impact. We all know that weeds and animal pests have a huge impact on our native flora and fauna, smothering our native plants, displacing or preying on our native fauna and changing the composition of our natural environments. Its important to control these animal and plant pests, to reduce the impacts on our native species and habitats.

Why do we control weeds and pests?

There are some very well organised groups in New Zealand which undertake weed and pest control on a volunteer basis. There are also a number of people who undertake weed and pest control because conditions of a resource consent or a consent notice require them to. In these cases, this is usually because a resource consent relies on some form of environmental mitigation or compensation. An example is bush or wetland based subdivisions, which rely on the protection of natural features to assist in offsetting adverse environmental effects. An important part of the mitigation “package” is ensuring that weeds and animal pests don’t significantly impact on these natural areas.

Making a Weed and pest control plan

If you’re meeting the requirements of resource consent conditions or a consent notice, first make sure there isn’t an approved weed and pest control plan already. Often these get approved as part of the resource consent process.

Identify the weeds and pests

If there isn’t an approved plan, or you’re doing weed and pest control for another reason, you should start off by writing a plan. Its likely that you will need a professional to assist you with your plan; identifying the species present and how you should control them is specialist knowledge. We work together with ecologists well experienced in this work, who can assist you.

The first task is undertaking a weed and animal pest survey, so you know what is actually present on the site and how abundant it is. Take special care to note any species which are a biosecurity risk. You should also look at the Regional Pest Management Strategy. This sets out the priorities and goals for pest management in your region.

This information from the Department of Conservation also assists with animal pests

It’s important you know what’s present and how abundant it is, and this will heavily influence the method of control and ongoing management, and how effective it will be. There will also be options to consider depending on the species present, such as toxins that target specific species (minimising the risk to other species), and self-setting traps that are more efficient in some cases and reduce labour needs.

How to control weeds and pests

The control methods vary depending on what the species is you’re controlling and the location. For example, control of weeds near watercourses needs to be different to areas away from water. Control of animal pests could include traps, shooting and toxins. The type of toxin and density of traps needed varies. Again, this is something we recommend you seek specialist help with. It may seem more money up front, but there’s little point in trying to control pests and weeds in an adhoc manner, wasting time and money and not getting the results you want.

Animal pests are typically controlled by trapping, shooting or by the use of toxins. There are a number of ways to control plant pests, including:

Drill and fill: generally best for big trees, uses less herbicide than most other methods and uses minimal amounts of water. Can generally be used all year round. Aim is to access cambium layer (under bark) so deep holes are not necessary. Only suitable for use in areas where eventual tree fall will not pose a risk to people or property.

Cut and squirt: this is good for soft trees (quicker to do than drilling). Cut a notch in a downward angle in the trunk and squirt concentrated herbicide in notch. Use drench gun and pack. Generally use all year round.

Frill: usually inferior to drilling as it uses more herbicide and requires complete ring around trunk to be made.

Vial treatment: use to give selective control of rhizomatous or layering creepers (jasmine, convolvulus, ivy, etc.). Individual flower vials are ideal for this, and are available from garden centres.

  • Cut vines 5-10 m apart, place end of vine in bottom of bottle containing concentrated herbicide. Vine sucks up herbicide and kills 2-to-many metres away.

  • Follow up monthly on missed spots

Stump paint: “painting” of herbicide to cut stump surface. Solution is usually 10% herbicide in water.

Weed wipe: this is particularly useful for grasses, rushes and soft herbs. Non-selective herbicides (eg glyphosate) can be made to act in a selective manner using a hockey stick type wiper. Likewise a residual herbicide (e.g. Metsulfuron, Amitrole, 2,4-D) can be applied by wiper to minimise or even eliminate residues, as the herbicide is contained within the plant rather than drifting or dripping onto the ground. Most or all of the herbicide is broken down within the weed. Look for a weed wiper that has a narrow or controlled release reservoir.

Hand dig: usually only suitable if entire root system can be dug out. Soil disturbance can lead to more weeds. Not recommended for resprouting species (e.g. tradescantia), as any fragments left will regrow.

Foliar spray: can be used to apply non-selective herbicides semi-selectively.

Weed mat: offers good control of many submerged aquatic weeds, especially non-seeding species. However it is expensive and time consuming to install.

Machine dig: occasionally useful to remove hard-to-kill individual plants (eg Arundo, bamboo) or to clear aquatic plants where control can be achieved by digging and the removed plants are guaranteed to perish on dry land. Obviously machine digging is an extreme measure, causing a host of environmental effects, and should only be used where the weed has high potential and no other control method exists.

Implementing the Plan

When looking at the plan, think about “easy wins” and what’s going to give you the best results fastest. This could include:

  • Controlling the weeds you have the least of,

  • Targeting climbing species. These are smothering the other plants.

  • Remove seed sources, including removing flowers from mature plants. This contains the weeds.

If the area affected is large, take a targeted approach and deal with smaller sections at a time.

Once the weeds are removed, it’s easier for weeds to recolonise; plant the areas with natives to reduce the potential for this to happen. You may be able to get funding from your local Council or other community groups/ grants for this. Remember control this isn’t a one- off task; control means that you need to go back regularly or your efforts may be in vain.

Working together

Often, a natural feature spreads over more than one site. It functions as one habitat or ecological system, not based on title boundaries. In these cases, it’s of benefit to work with your neighbours on weed and pest control, managing the feature as a whole.

Looking to subdivide your rural site?

The Planning Plus team has extensive experience in rural development, having worked in resource consents in this area since 2003. We will help you understand the District Plan rules affecting rural development, including protecting natural features.

We also have blogs on subdivision and resource consent costs which you may find useful.

Get in contact with our friendly team, for honest and reliable advice.

Hannah Thomson is a Director of Planning Plus and has over 17 years of resource management experience working in both local government and the private sector. Hannah has a wide range of experience including commercial, rural, residential and coastal development and subdivision on small to large scales and appearances at both Council and Environment Court as an expert witness for mediation and hearings. Hannah has assisted Councils with policy development and has also assisted private individuals with submissions to Council.

Disclaimer As with all our blogs, the information detailed here is general in nature and meant as a preliminary guide only. This should not be substituted for your own investigations or use of your own professional’s. Planning Plus is not liable for any errors or omissions.

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