Aerial control

One of the biggest challenges of dealing with wilding conifers is the remote and mountainous terrain they grow in. Helicopters allow access to wilding conifers that would be difficult or impossible to reach otherwise.

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They can be used for:

  • Aerial Basal Bark Application (ABBA) of herbicides directly to the trunks of wilding conifers.
  • Skid-hopping – carrying people with herbicide spray or mechanical equipment (usually chainsaws) and dropping them off for the removal operation.
  • Aerial foliar boom spraying of dense stands.

These control methods can only be carried out by highly skilled and trained operators who understand the risks and best practices. See further down the page for details on each method.


Skid-hopping is ideal for carrying conifer control teams and equipment to remote or hard-to-access locations. Once there, operators will use the most appropriate methods as outlined in the following pages:

For Ground control of scattered seedlings and small trees (less than 20-30cm diameter at breast height) - please follow the quick link below

For Ground control of larger trees and dense stands - please follow the quick link below

Aerial Basal Bark Application (ABBA)

Aerial Basal Bark Application of herbicide is effectively the same as the Ground Basal Bark Application (GBBA) method, except a helicopter carries the spray operator from tree to tree. The operator remains in the helicopter, while using a spray wand (‘lance’) to apply herbicide to the bark at the top of the tree. The herbicide then runs down the stem to the base. This can be the most cost-effective way to control medium-sized trees spread widely across the high country, and may be the only practical way to control trees growing on cliff faces. Click this link for more about Basal Bark Application methods.

In Basal Bark Applications on wilding conifers, a registered herbicide is used in conjunction with a carrier oil. Vegetable oils (including biodiesels) are recommended as carriers – as these are safer and more environmentally friendly than mineral oils (see SCION research’s 2017 carrier oil review). Proprietary Basal Bark Application herbicides are often ready-mixed.

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Aerial foliar application using a boom

Spraying herbicide onto conifer needles from the air can be an economical control method where wilding conifer forests have a canopy cover of over eighty percent.

Only EPA-certified chemicals are able to be used in a boom spray operation. Helicopters are usually used, but at times fixed-wing aircraft may be an option for aerial boom spraying.  
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Helicopter specifications

  1. Because total wetting of all the foliage is required, the liquid herbicide mixture is to be boom sprayed at the right droplet size and application rates. This will ensure good foliar coverage.

  2. To limit the spray released into the rotor vortices and significantly reduce drift, spray booms should not exceed 80 percent of the rotor length.

  3. The herbicide should be discharged at a height of 3 – 4 m above the canopy, if possible.

Further information on control methods

Wilding control: Guidelines for the control of wilding conifers summarises the benefits of the various control methods and helps you choose the appropriate method, plus the costs of each method.

Monitor your site

Besides removing trees, controlled areas need to be monitored regularly. Conifer seeds are viable for about 6 years. Check controlled sites after 2-3 years and hand-pull any seedlings that have sprouted. Repeat this 2-3 years later. Generally, if the site is clear of wildings after 5-6 years from the original control, the operation will be complete, but occasional checks should still be made. Although if there is a seed source that cannot be removed, then control will be ongoing.

We recognise however the need for a standard good-practice method of post-control monitoring. This will be developed in future.

Ground control: scattered seedlings and small trees

Ground control of scattered seedlings and small trees

Ground control: larger trees and dense stands

Ground control of larger trees and dense stands

Conifer identification

Wilding conifer identification guide

Site restoration

Replant or restore the area you have controlled

Post-control monitoring

Monitor to prevent re-infestation