A wilding conifer is easiest to kill while it is still small. Seedlings and small trees (up to 20 cm diameter at breast height) can be dealt with using hand and machine tools, or basal bark herbicide application.
As conifers increase in age, size and abundance, they become more difficult to remove, and costs rise exponentially. They also start producing seeds – which spread and compound the infestation. Removing sparse young seedlings can cost as little as $1/ha, but treating dense infestations may cost over $10,000/ha. Wilding control: Guidelines for the control of wilding conifers
There are two main ways to control wildings: physical (by hand or machine) and chemical. Seedlings and small trees can be controlled in the following ways:
See below for descriptions of each control type, and its good practices.
Hand-pull seedlings up to 30 cm tall, or ease them out of the ground with a tool such as a grubber or mattock. The smaller the seedling, the easier it is to remove. Finding the seedlings (for identification, please follow the quick link below) is the main challenge, but once they’re found, the job is straightforward. Volunteers are very helpful for this work.
Health and safety:
Cutting down with hand tools
Cutting down small and medium-sized conifers with hand tools is relatively simple, but labour intensive. It’s important to remove all branches and green foliage below the cut or apply herbicide to the stump or the tree may resprout (see Cut stump herbicide application below).
Loppers in use
Health and safety:
Chainsaws are useful for quickly cutting down dense stands of wildings, from small seedlings to saplings up to 15 cm in diameter at the trunk base; scrub bars (weedeaters with a tungsten circular blade) are used less often. Young trees may resprout from any green needles left at their base. So remove these, or else treat the stump with herbicide (see Cut stump herbicide application below).
Remove any green needles from the base
Operators need to be skilled and hold appropriate certifications.
Herbicides are used for chemical ring barking, or to reduce the risk of regrowth from a cut stump. Whenever you use herbicides, it’s essential to follow the safety and use instructions on the label. This includes wearing the proper protective clothing.
Also, when using herbicides, be careful of non-target species. Use low spray pressure at the right concentrations, spray directly on the tree, and avoid spraying or runoff into waterways.
Oil-based herbicide pre-mixtures chemically ring-bark unwanted conifers with trunk diameters of up to 20 cm. Apply the herbicide using a knapsack sprayer, with the nozzle set at low pressure to reduce spatter, and apply a wide collar around the basal bark (bark at the base of the trunk). This is less labour intensive than delivering herbicide internally to the trunk, such as ‘drill-and-fill’, which is outlined in control methods for larger wildings. It can take a year or two for a tree to die – so don’t worry if this doesn’t happen immediately.
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.
Ground Basal Bark Application
Operators need initial training in good practices to effectively use this technique. Click this link and see more about Basal Bark Application methods.
Where dead standing trees are not wanted, the trees can be felled with a chainsaw, scrub bar or handsaw and herbicide applied to the stump. The herbicide kills the root system and prevents regrowth. This is a good method on screes or where a thick grass sward surrounds the tree's base - ie. where it is very hard to get all the green needles around the base of the tree. Double-handling (cut stem and apply) is labour intensive, and herbicide needs to be applied to the stump at the time of felling.
If using X-tree Wet and Dry apply the herbicide to the bark on the remaining stump. Apply all other herbicides (eg a stump gel or metsulfuron methyl), to the top of the cut stump – particularly its edges (the ‘cambium’ layer).
Burn-offs can be a relatively inexpensive solution for small wildings. However burning carries significant risks and can be time consuming. Burning will require a resource consent and a fire permit.
Annual mob-stocking for long term control of small seedlings is a simple way of reducing wilding conifers in a farm setting. It’s only effective on very young seedlings (1-2 years old), and works best when combined with applying fertilisers to encourage other vegetation like grasses.
Fertilising controlled areas helps vegetation like grasses compete with wildings, but it may reduce native plant numbers. It’s a simple and effective option for professional farmers and best used in pasture and grasslands, especially when combined with grazing. However check your local nutrient management requirement sunder the RMA.
Depending on the machine size, mulchers can tackle seedlings through to trees with trunks up to 20 cm diameter. Mulching is a very cost-effective tool for dense stands of small- to medium-sized wilding conifers on smooth sites that aren’t too steep. However, tractor mulchers may fail to remove low green foliage, especially on uneven sites. They also create an ideal soil surface for new seedling invasion, so it’s important to monitor the site after mulching, and follow up. The choice of machine size important, as-is a skilled and experienced driver.
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 an appropriate method.
For controlling trees with diameters at breast height over 20-30 cm, please follow the quick link below to Ground Control of larger trees and dense stands.
For aerial methods, please follow the quick link below to Aerial Control of scattered trees and dense stands.
Besides removing trees, controlled areas need to be monitored regularly. Conifer seeds are viable for up to 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 6 years from the original control, the operation will be complete. 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.