Biosecurity

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Animal Pest Management

Many introduced pest species in Aotearoa New Zealand cause negative impacts on the country's indigenous biodiversity with the potential to harm local economies and communities. In order to reduce any actual or possible consequences associated with pest species, central and regional government are tasked to manage pests under the Biosecurity Act 1993. Pest species are listed in regional pest management plans.

Weeds in Aotearoa New Zealand and where to find expert advice:

Weeds are one of the major threats to Aotearoa New Zealand ecosystems and food production areas. The below information presents weed management techniques for common types of weeds found in Aotearoa New Zealand.

The brief outline of techniques below is how to manage tree weeds, vines, climbers, weeds tolerant of shading, wetland weeds, and weeds around planting areas. We have included a range of treatment techniques, including herbicides, hand, and mechanical control, as well as alternative methods of weed management.

NZARM has compiled summary information below, further information can be found from expert organisations, see the Resources links below. Beyond this list it is recommended that you contact your regional council to understand their Regional Pest Management Plan or link up with one of their experts to get comprehensive advice.

From a policy perspective the Biosecurity Act 1991 enables central and regional government to manage invasive weeds. It is the responsibility of Regional Council’s to take the initiative in preventing, reducing, and eliminating harmful weed species across their region.

Tree weeds

Aotearoa New Zealand is home to several tree weeds that pose significant threats to native flora. The choice of control method depends on various factors, including the type of tree weed, its size, growth habit, and the surrounding vegetation. It is important to consider the potential impact on non-target plants, the effectiveness of herbicide absorption, and the safety precautions associated with each technique. Consulting with a professional or seeking expert advice is recommended to determine the most suitable control method for specific tree weed species and site conditions. managing tree weeds, consider the following techniques:

Selective herbicides such as triclopyr (e.g., Garlon) or glyphosate (e.g., Roundup) can effectively target tree weeds without harming desirable trees. Systemic herbicides are particularly effective as they are absorbed by the tree weed and translocated throughout the plant, leading to complete eradication.

For smaller tree weeds, hand-pulling or cutting at ground level can be effective. However, ensure complete removal of the roots to prevent regrowth. For larger tree weeds, mechanical techniques such as chainsaws or brush cutters may be necessary. Practical examples include the use of chainsaws to cut down and remove invasive tree weeds like Wilding Pine (Pinus contorta).

Frilling involves making several downward cuts into the bark of the tree weed, creating channels for herbicide application. This method is useful for controlling woody tree weeds and is often used when the tree is too large for other treatment methods. Frilling is effective for herbicides that require absorption through the bark.

Frilling

This method involves cutting down the tree weed and immediately applying herbicide to the freshly cut stump or the outer cambium layer. The herbicide is absorbed into the remaining root system, preventing regrowth. Cut and stump treatment is commonly used for controlling woody tree weeds and is effective for both selective and non-selective herbicides.

Cut and stump treatment

Foliar spray involves applying herbicide directly to the foliage of the tree weed. The herbicide is absorbed by the leaves and transported throughout the plant, ultimately killing the weed. Foliar spray is useful for controlling a wide range of tree weeds, particularly herbaceous ones. Selective herbicides are often preferred in situations where desirable vegetation is present nearby.

This technique involves drilling holes into the tree weed's trunk and injecting herbicide directly into the holes. The herbicide is then distributed throughout the vascular system, effectively controlling the weed.

Basal bark treatment involves applying herbicide and an oil-based carrier mixture to the lower portion of the tree weed's stems or trunks. The herbicide is absorbed through the bark and translocated to the roots, preventing regrowth. Basal bark treatment is effective for controlling woody tree weeds, especially when treating individual plants within a larger population.

Soil application involves applying herbicide to the soil around the base of the tree weed. The herbicide is absorbed by the roots, effectively controlling the weed from below the ground. This method is commonly used for controlling perennial tree weeds, particularly those with extensive root systems.

Girdling is the process of removing a strip of bark around the circumference of the tree weed's trunk, disrupting the flow of nutrients and water. This technique can be used in conjunction with other control methods, such as herbicide application, to enhance effectiveness. Girdling is useful for controlling woody tree weeds, especially those with large-diameter trunks.

The choice of control method depends on various factors, including the type of tree weed, its size, growth habit, and the surrounding vegetation. It is important to consider the potential impact on non-target plants, the effectiveness of herbicide absorption, and the safety precautions associated with each technique. Consulting with a professional or seeking expert advice is recommended to determine the most suitable control method for specific tree weed species and site conditions.

Vines and climbers

Aotearoa New Zealand's temperate climate and diverse landscapes means that we often face challenges from invasive vines and climbers. Vines and climbers can be a particular challenge when planting. To manage these weeds effectively, consider the following techniques.

Non-selective systemic herbicides like glyphosate (e.g., Roundup) can be used to target vines and climbers. Apply directly to the foliage or use a cut-and-spray technique, ensuring thorough coverage for optimal results. For instance, glyphosate-based herbicides have been used successfully to control invasive vines like Old Man's Beard (Clematis vitalba).

A very useful restoration technique pioneered by regional council restoration staff in the early 2000s (as far as we know) is to initially plant native species that are resistant to broadleaf spray (e.g., Carex, toetoe, flax, cabbage tree) and use broadleaf selected herbicides that can't damage these plants but will control the invasive vines and climbers.

Pros:

  • Works in small riparian areas
  • Will shade small waterways
  • Filters overland flow
  • Stabilises bank more than grass.
  • Can selectively spray broadleaf weeds without risk to native planting.

Cons:

  • Plant cost
  • Sot as much shade generated as tree planting
  • Less habitat for birds.

Weed control around native planting areas video

For smaller vines and climbers, manual removal by hand-pulling or cutting can be effective. For larger infestations, mechanical techniques like mowing or using a brush cutter may be necessary. Examples include the mechanical removal of invasive vines like Banana Passionfruit (Passiflora tripartita) using brush cutters.

Manual removal involves physically pulling, digging, or cutting out the vine and creeping weeds. This method is effective for small infestations and can be combined with other control methods for better results. Examples include pulling out annual vines like bindweed (Convolvulus arvensis) or cutting back perennial creeping weeds like ground ivy (Glechoma hederacea) or rolling wandering willie (Tradescantia fluminensis) with a garden rake.

Smothering or mulching involves covering the area with a layer of materials such as cardboard, plastic sheets, or organic mulch. This technique deprives the vine and creeping weeds of sunlight, inhibiting their growth. It works well for suppressing weed germination and can be useful for controlling ground covers like English ivy (Hedera helix) or spreading vines like kudzu (Pueraria montana).

Herbicides can be used to effectively control vine and creeping weeds. Selective herbicides are preferred when desirable plants are present nearby, while non-selective herbicides can be used when the infestation is severe or when there are no desirable plants to preserve. Examples include:

Foliar Spray: Applying herbicide directly to the foliage of the vine or creeping weed. This method is suitable for herbaceous vines like bindweed or broadleaf creeping weeds like prostrate spurge (Euphorbia humistrata).

Cut and Stump Treatment: Cutting the vine or creeping weed at the base and applying herbicide to the cut stump. This technique is useful for controlling woody vines like English ivy or invasive creeping plants like Japanese honeysuckle (Lonicera japonica).

Basal Bark Treatment: Applying herbicide mixed with an oil-based carrier to the lower portion of the vine or creeping weed's stems. This method is effective for woody vines such as oriental bittersweet (Celastrus orbiculatus) or creeping vines like creeping buttercup (Ranunculus repens).

Vine wrapping involves physically wrapping or encasing the vine or creeping weed in a material that prevents it from growing or accessing sunlight. Examples include wrapping invasive vines like wisteria (Wisteria spp.) with burlap or using specially designed vine wraps to restrict the growth of creeping plants.

Regular mowing or trimming can help control vine and creeping weeds by reducing their vigor and preventing seed production. This method is particularly useful for controlling grassy creeping weeds like Kikuyu grass (Pennisetum clandestinum) or spreading vines like trumpet creeper (Campsis radicans).

Introducing natural enemies, such as insects or pathogens, that specifically target the vine or creeping weed can provide long-term control. Biological control methods require careful consideration and should be carried out under the guidance of experts to prevent unintended ecological consequences.

A lot of research goes into testing biocontrol agents before they are released. Safety of the people and the environment is paramount. Research of new biocontrol agents can take 5 to 10 years and can be costly to undertake.

Researchers usually only consider biocontrol agents that are the natural enemies of target weeds and pests, so it is unlikely the biocontrol agent will attack and harm non-target plants and animals. Researchers assess the risk of damage to non-target plants using procedures endorsed internationally. Biological control agents are approved by the Environmental Protection Agency (EPA) in Aotearoa New Zealand.

Shade tolerant weeds

Weeds that thrive in shaded areas can be particularly challenging to manage in Aotearoa New Zealand's forests. Below are some techniques to combat them.

Selective herbicides formulated for shade-tolerant weeds can be used. Care should be taken to protect desirable plants from accidental herbicide contact. For instance, the use of selective herbicides like metsulfuron-methyl (e.g., Escort) has been effective in controlling shade-tolerant weeds such as Tradescantia (Tradescantia fluminensis).

Regular hand-weeding or cutting of shade-tolerant weeds is recommended. Ensure complete removal of roots to minimise regrowth. Manual removal of shade-tolerant weeds like Ivy (Hedera helix) or Periwinkle (Vinca major) can be effective.