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Read our Winter/Spring 2024 Update

Control Methods

Wilding control methods used in New Zealand include everything from hand pulling young seedlings to using helicopters and logging equipment. Around the country, highly skilled contractors (and lots of skilled volunteers too) carry out control work almost all year around in all sorts of landscapes.

Under the National Wilding Conifer Control Programme, choosing the right control method for each operation involves considering a lot of information about the wilding infestation and the area around it. Especially key are safety, cost-effectiveness, and what will work best (that depends on the species, age, size and density of wilding trees). Other factors include how easy it is to get people and equipment to the site, and being careful with the surrounding environment. The Programme's good practice guides explain where and how each method should be used.

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Ground Control techniques

Chainsaws and hand tools
  • Chainsaws and/or hand tools are used to cut small to medium-size trees at their base. Stumps are treated with herbicide gel, so the trees don’t regrow. If any branches or needles, are left on a stump, the tree can grow back.

    Check out the Cut Stump Good Practice Guide and video

Drill and Fill
  • Medium to large trees may be cut down or “drilled and filled” – herbicide is injected directly into holes drilled in the trunk, to kill the tree from the inside. Drill-and-fill is used on wildings that are large or too dangerous to fell using a chainsaw, where felling would damage surrounding vegetation, or in sensitive areas, such as close to native habitats.

    Check out the Drill and Fill Good Practice Guide and video

Hand pulling
  • Very small seedlings are simply hand-pulled by the roots and left in place to break down.

Aerial Control techniques

Aerial Basal Bark Application (ABBA):
  • ABBA involves ring-barking trees with herbicide, which is applied to the trunk of one tree at a time using a wand by an operator on board a helicopter, under guidance from the ABBA Good Practice Guide.
  • It is used for widely scattered trees or where trees cannot be safely accessed at ground level.

    Check out the ABBA Good Practice Guide

Aerial Foliar Spray Application (AFSA):
  • AFSA (or “boom-spray”), involves applying herbicide to the foliage of multiple trees by helicopter with a fixed spray boom, to control dense infestations while protecting the surrounding landscape.
  • AFSA is used in less than one percent of all wilding conifer control operations in New Zealand, and only after careful planning to ensure the safety of people, animals, property, and surrounding environment.
  • The National Wilding Conifer Control Programme Good Practice Guides for AFSA include routine testing of any nearby water bodies (including wetlands, flowing water ways or supply wells) both before and after spraying, and again after rainfall. This is a precautionary practice (as of 2021) to ensure measures to protect the environment are effective in all locations and conditions.

    Check out the AFSA Good Practice Guide 

Other control methods

The methods below are used in the National Programme, but are less common.

Aerial foliar spot spraying
  • A method not widely use in the Programme.
  • This method is being trialled as an alternative to ABBA (chemical ring-bark) in scattered infestations of very large trees where ABBA is not feasible or may not be effective due to large circumference of trees or trees with multiple leaders.
  • Herbicide is spot sprayed directly onto foliage (as opposed to the bark, in ABBA), one tree at a time by wand (as opposed to boom spray over a wide area, in AFSA) either from a helicopter or via drone.

    (A Good Practice Guide is being developed for this technique)

Harvesting
  • Where there is safe access for trucks and machinery, mature trees can sometimes be harvested.
  • The often remote and steep locations of wilding conifer stands means that harvesting is often expensive.
  • The high degree of variability in trees size and quality in wilding conifer stands means harvesting is generally only practical where the costs can be covered by the sale of the logs, wood chip, firewood, or wood fibre which may be used as biofuel.

Felling to windrows
  • Large trees can be felled and lain in windrows to break down on site
  • Used when harvesting and transport of felled trees is not feasible, and spraying is not appropriate (this could be for a range of reasons)

Controlled burning
  • The use of controlled fire as a method of removing wilding conifers is not widely done in New Zealand, but can be used in certain circumstances, under controlled conditions – in consultation with Regional Authorities adjoining landowners and Fire and Emergency NZ.  

 

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