4. Can it be beaten?

The honest answer is: not yet — but we are getting closer. Here is what we know works, what does not, and where new approaches are changing the picture.

Over the past 90 years, New Zealand has thrown almost every available tool at gorse — herbicides, fire, machinery, goats, insects, fungi, and a great deal of human effort. Some approaches work well in some settings. None has solved the problem comprehensively. And on steep, inaccessible terrain — exactly the kind found across Wellington's hills — most conventional methods struggle or fail entirely.

This page gives an honest assessment of the current state of gorse control: what each method can do, what it cannot, and why the combination of emerging technology and smarter integrated management is creating real grounds for optimism for the first time in decades.

Understanding the limits of existing methods is not pessimism — it is the foundation of better solutions. The Wellington Region Hills Environmental Trust was established precisely because the conventional toolkit has not been sufficient, and new approaches are needed for Wellington's challenging terrain.

🧪 Method 1: Herbicides The most effective conventional tool — with significant limitations

Chemical herbicides remain the most reliable method for killing established gorse plants. Several products are registered for gorse control in New Zealand, and when applied correctly they can kill mature plants with a high success rate.

Herbicide: How it works and effectiveness on gorse

Triclopyr (e.g. Grazon)

Systemic herbicide absorbed through foliage and bark. Highly effective on mature gorse when applied during active growth (spring/early summer). Widely used by councils and contractors.

Picloram + triclopyr (e.g. Conquest)

Combined formulation for tough situations. Effective on large, established stands. Can affect native species if drift occurs — requires careful application.

Metsulfuron (e.g. Meturon, Escort)

Effective on gorse seedlings and younger plants. Less effective on large mature shrubs. Useful as a follow-up treatment after initial clearing.

Aminopyralid (e.g. Milestone)

Newer formulation with residual soil activity, useful for reducing seedling germination from the seed bank. Growing use in NZ weed management.

Glyphosate (e.g. Roundup)

Limited effectiveness on gorse due to thick, waxy cuticle on spines that resists absorption. Generally not recommended as a primary gorse treatment.

Why herbicides alone are not enough

Herbicides face a fundamental challenge with gorse: the seed bank. Killing the plants above ground does not touch the reservoir of viable seeds waiting in the soil. A successful spray programme that removes all visible gorse from a site will often be followed by a dense flush of seedlings germinating from below — and those seedlings must be treated again, typically within one to two seasons.

On Wellington's steep hill terrain, herbicide application faces additional challenges. Many gorse-infested hillsides are inaccessible to ground-based spray equipment — too steep for vehicles, too dense for safe manual application, and too close to waterways or native vegetation for broad-acre aerial spraying without unacceptable non-target damage. This is the core gap that new technology, particularly agricultural drones, is beginning to fill.

Verdict: Effective but incomplete

Herbicides are the most reliable tool for killing established gorse. They work best when followed by immediate native planting or pasture establishment to occupy the ground before seedlings emerge. On flat or gently sloping terrain, ground-based application is practical. On steep Wellington hill terrain, delivery is the constraint — and that is where drones are changing the equation.

🔧 Method 2: Mechanical control Clearing the visible — but not the invisible

Mechanical control covers a range of physical methods for removing gorse biomass: cutting, mulching, slashing, bulldozing, and hand-pulling. These approaches can be highly effective at removing the above-ground plant rapidly and at scale — but they carry significant limitations.

What mechanical control can do

• Clear large areas of gorse quickly when machinery can access the site

• Reduce fuel load and fire risk in gorse-covered areas near urban development

• Open up terrain for follow-up herbicide treatment or native planting

• Create access corridors through dense gorse for other restoration work

What it cannot do

• Access steep, rocky, or wet terrain where machinery cannot safely operate — a severe constraint in Wellington's hill country

• Address the seed bank — mechanical disturbance of the soil during clearing actually promotes germination from the seed bank, often producing a worse flush of seedlings than the original stand

• Kill the root system — gorse frequently resprouts from the crown and root fragments after cutting, requiring follow-up chemical treatment

Research is unambiguous on the seed bank issue: mechanical methods of gorse removal, though highly successful at clearing above-ground material, induce chronic soil erosion and land degradation and should be used sparingly without immediate follow-up planting and herbicide treatment of regrowth. The disturbance that clearing creates is the same disturbance that triggers mass seedling germination.

Verdict: Useful but terrain-limited and seed bank blind

Mechanical clearing has a clear role in gorse management — particularly as a first step to open terrain for herbicide follow-up and native planting. But it cannot be used in isolation, it cannot reach Wellington's steepest terrain, and it must be paired with immediate revegetation to avoid triggering a worse seedling flush than the original infestation.

🔥 Method 3: Fire Counter-productive in almost all Wellington contexts

Fire has historically been used as a gorse control tool

-burning the above-ground plant to clear large areas quickly. In Wellington's context, fire is not a recommended management tool and in most situations actively makes the problem worse.

The reasons are well understood. Gorse seeds have a hard coat that heat breaks open — a burn-off is effectively a mass germination trigger for the seed bank. A hillside that looked cleared after burning can be covered in gorse seedlings within one growing season. The subsequent infestation is often denser and more difficult to treat than the original stand.

In Wellington's windy environment and steeply broken terrain, the additional risks of uncontrolled fire spread, proximity to residential areas, and injury to volunteer or contractor workers make fire an unacceptable tool in most situations. The February 2024 Port Hills fires near Christchurch — weeks of burning on gorse-covered slopes above suburban areas — provide a clear illustration of what fire in comparable terrain looks like.

Verdict: Not recommended for Wellington's urban-fringe hill terrain

Fire may be used in some rural flat-land contexts under controlled conditions. In Wellington's steep, wind-prone, urban-fringe hill environment it is not appropriate as a primary control tool. Its effect on the seed bank makes the long-term gorse problem worse, not better, and the risk to people and property is not acceptable.

🐐 Method 4: Goats and targeted grazing Promising — but logistically challenging on Wellington's hills

Goats are well established as an effective biological tool for gorse control. Unlike sheep or cattle, goats will actively browse on young gorse shoots, progressively weakening and killing plants over time. Research has confirmed that intensive rotational grazing with goats — at sufficient stocking densities — can control gorse in pastoral settings.

The Massey University weeds database notes that goats will graze gorse and can kill it. The key parameters are stocking density (high enough to maintain pressure on regrowth) and rotation (regular return to prevent recovery).

Practical limitations for Wellington hill terrain

• Goats require secure fencing to contain them and prevent damage to native vegetation — on steep, rocky hillsides this is expensive and difficult to install

• Wellington's reserve land and cross-boundary gorse infestations involve multiple landowners — coordinating grazing access across boundaries is complex

• Goat control for environmental purposes on steep public land raises liability and biosecurity considerations that councils manage cautiously

• Goats are effective on young and medium-aged gorse but have limited impact on very large, established mature plants

Where goats can be deployed — on lifestyle blocks, farms, and accessible reserve margins — they offer a cost-effective and chemical-free option that pairs well with follow-up native planting. The Trust considers targeted grazing partnerships with willing landowners as one of its practical tools.

Verdict: Effective where logistics permit

Goat grazing is one of the most promising low-chemical approaches to gorse management and should be part of the toolkit where terrain and land tenure allow. Its limitation in Wellington's context is logistical rather than biological — fencing, access, and cross-boundary coordination present real barriers that require the kind of multi-party facilitation the Trust exists to provide.

🪲 Method 5: Biological control agents Ninety years of research — with mixed but improving results

New Zealand has been investigating biological control of gorse since the 1920s — among the earliest biocontrol programmes for any weed species in the world. Seven different agents have been introduced over this period, targeting the plant's seeds, foliage, and shoots.

Agent status and effectiveness

Gorse seed weevil (Exapion ulicis) — introduced 1928–1931

- Destroys approximately 35% of spring seed crop. Established throughout NZ.

- Limited by gorse's autumn flowering (weevil is univoltine — one generation per year).

Gorse pod moth (Cydia succedana) — released 1992

- Together with seed weevil, combined seed-feeding agents can destroy up to 90% of annual seed crop in some years.

- Reducing the seed bank over long periods.

Gorse spider mite (Tetranychus lintearius) — introduced 1989–1990

- Causes significant foliage damage in outbreak years, reducing growth and flowering.

- However, predatory insects (ladybirds, predatory mites) prevent sustained population levels needed to kill mature plants.

Gorse soft shoot moth (Agonopterix umbellana) — released 1988

- Established throughout NZ. Damages shoot tips, reducing growth.

- Contributes cumulatively to plant stress over time.

Gorse colonial hard shoot moth (Pempelia genistella) — released 1988

- Established in South Island; patchy establishment in North Island including Wellington region.

- Less consistent effectiveness nationally.

Gorse thrips (Sericothrips staphylinus) — introduced 1990

- Established but spread slowly.

- Causes foliage damage in experimental conditions. Overall effectiveness at landscape scale remains limited.

The honest verdict on biocontrol: progress but not a solution

A major 2022–2024 Manaaki Whenua Landcare Research survey of 17 sites across New Zealand produced a sobering finding: despite biological control agents being present at most sites, gorse is as healthy and as dense as it has ever been. Dead gorse made up just 8.8% of gorse stands on average. The agents are present and causing damage, but not at a level that is reducing gorse cover at the landscape scale.

This does not mean biological control has failed. The seed-feeding agents in particular are doing genuine work on the seed bank, and chronic foliage damage may be slowly weakening long-lived plants. But biological control alone — at the current level of agent efficacy — is not sufficient to reduce the gorse problem in Wellington's hills over any timeframe relevant to living people.

The Landcare Research programme continues, with active management of agent populations and ongoing research into a bioherbicide based on the fungus Fusarium tumidum — which has shown promising results in laboratory trials and may eventually provide a biological alternative to chemical herbicides for certain situations.

Verdict: Contributing but not sufficient on its own

Biological control agents are reducing the gorse seed bank and causing cumulative plant stress, but are not killing gorse at the landscape scale needed to reverse Wellington's hill infestations. They are a valuable background component of an integrated management programme — but not a substitute for active intervention on priority sites.

🚁 Method 6: Agricultural drones The game-changer for steep and inaccessible terrain

This is where the picture changes. Agricultural drone technology — developed primarily for large-scale cropping and now rapidly adapted for environmental management — is solving the core constraint that has defeated conventional gorse control on Wellington's steep hill terrain: safe, precise access.

Agricultural spraying drones are now operating commercially in New Zealand, specifically targeting gorse and other invasive species on steep, inaccessible terrain. Multiple New Zealand operators are using platforms such as the DJI Agras T50 — capable of carrying 40 kg spray payloads, operating with centimetre-level GPS accuracy (RTK), covering large areas in a fraction of the time required for manual application, and accessing slopes, gullies, and cliff faces that no ground-based method can safely reach..

What drone spraying offers for Wellington's hills

Terrain access Drones handle steep slopes, gullies, wet ground, and rocky faces with ease — exactly the terrain that defeats conventional machinery and makes manual work hazardous. Wellington's inaccessible gorse-covered hillsides are precisely the use case these platforms were designed for..

Precision targeting GPS-guided application means herbicide reaches only the target plants. Drift is minimised by the drone's rotor downwash, which drives spray downward into the canopy. This is critical near native vegetation, waterways, and residential areas.

Reduced herbicide volume Drone application achieves effective coverage with substantially less herbicide than helicopter or ground-rig spraying, reducing chemical use and cost while improving environmental outcomes.

Operator safety No contractor needs to enter steep, unstable, or prickly gorse terrain. The safety risk to workers — which is a genuine concern on Wellington's steep and often wet hillsides — is effectively eliminated.

Speed and scale A modern agricultural drone can treat far larger areas per day than manual teams, at lower cost per hectare than helicopter spraying. This changes the economics of treating large-scale hill country infestations.

Flexible timing Drones can operate at dawn, dusk, or in small weather windows when wind conditions are calm — critical in Wellington's frequently windy environment where spray drift is an ongoing concern.

How the Trust intends to use drone technology

The Wellington Region Hills Environmental Trust is exploring drone-assisted herbicide application as a primary tool for treating gorse on the steep, cross-boundary hillsides that conventional methods cannot safely reach.

Our approach involves:

• Mapping priority treatment sites using aerial photography and GIS data from Greater Wellington Regional Council and Wellington City Council

• Engaging licensed drone spray operators with experience in hill terrain and environmental applications

• Coordinating access and consent across multiple landowners and agencies before treatment

• Sequencing drone treatment with immediate native planting to establish ground cover before seedlings emerge

• Monitoring treated sites to trigger follow-up treatment of seedling regrowth within the first one to two seasons

Verdict: The key innovation for Wellington's inaccessible terrain

Agricultural drone technology does not solve every aspect of gorse management — the seed bank, native planting, and long-term monitoring remain essential. But it solves the single biggest practical constraint in Wellington's hill context: how to safely and precisely apply herbicide to steep, inaccessible terrain at reasonable cost. This is why drone-assisted treatment is central to the Trust's operational model.

The real answer: integrated management

No single method beats gorse. The evidence from ninety years of New Zealand experience is clear: gorse management works when multiple tools are applied in sequence, and fails when any single tool is relied on alone.

Effective integrated gorse management — particularly on Wellington's steep, ecologically sensitive terrain — follows a consistent logic:

Actions and rationale

1. Site assessment

Map the extent of infestation, identify terrain constraints, assess proximity to waterways and native vegetation, establish baseline native species present. This stage is critical for choosing the right method combination and cannot be skipped.

2. Priority treatment

Apply herbicide to established plants, using drone delivery on steep or inaccessible terrain and ground-based application where accessible. Time treatment to active growth periods (typically spring in Wellington) for maximum uptake. Allow 6–8 weeks for the herbicide to fully translocate before follow-up assessment.

3. Mechanical follow-up (if needed)

On accessible terrain, mulch or cut dead material to reduce fire fuel load and open the site for planting. On steep terrain, allow material to collapse in situ — this provides temporary ground cover that suppresses some seedling germination.

4. Immediate native planting

This is the most critical and most underinvested step. Native plants must go in as quickly as possible after treatment to compete with emerging seedlings from the seed bank. Species selection should match the site — local provenance, wind and drought tolerant, and structurally competitive with gorse seedlings.

5. Seedling management (Year 1–2)

Monitor for seedling germination from the seed bank. Treat emerging gorse seedlings with herbicide before they become established — metsulfuron is effective on young plants. This is the phase where most programmes fail if funding runs out.

6. Native canopy closure

Once native plants are tall enough to shade out gorse (typically 3–5 years on Wellington's sheltered sites, longer on exposed terrain), gorse regeneration naturally declines. The goal is to get native species to this point before the seed bank re-invades the site.

7. Long-term monitoring

Establish monitoring plots to track native species establishment and gorse regrowth over time. Adjust management as needed. Brief post-treatment assessments 5 years out are not sufficient — 10+ year monitoring is best practice.

Proof it can work: Hinewai Reserve

The most compelling New Zealand evidence that gorse can eventually give way to native forest comes from Hinewai Reserve on Banks Peninsula — and it comes with an important nuance.

At Hinewai, the late Hugh Wilson adopted a 'benign neglect' approach: rather than treating gorse, he simply removed grazing animals and allowed natural succession to proceed. Within approximately 15–20 years, native broadleaved species had grown up through the ageing gorse canopy and replaced it with native forest — a much faster succession timeline than through mānuka or kānuka.

This is real and significant. But it depends on conditions that do not always apply — particularly in Wellington:

- A nearby native seed source is essential. Without seed dispersal from established native bush, native species simply do not colonise old gorse naturally at a meaningful rate

- Freedom from browsing animals (deer, goats, possums) is critical. Wellington's hill country is not uniformly free of these pests

- The timeline is 15–30 years or more. In urban-fringe areas with fire risk and community access expectations, this is not always acceptable

- Research has confirmed that gorse and kānuka produce quite different successional forests — gorse sites have lower native species diversity than kānuka sites at comparable stages, meaning passive succession through gorse comes at a biodiversity cost

Hinewai shows that nature can reclaim gorse-covered land given the right conditions and enough time. It does not show that active management is unnecessary — particularly in Wellington's complex, fire-prone, urban-interface terrain where waiting 30 years is not an option and native seed sources are often insufficient to populate large gorse-covered slopes without active planting.

So — can gorse be beat?

Yes — on a site-by-site basis, with the right combination of tools, sufficient resources, and long-term commitment. The evidence from New Zealand and internationally is that well-executed integrated management programmes — herbicide treatment, followed by native planting, followed by seedling management over two to three seasons — can permanently reduce or eliminate gorse from priority sites.

What has not worked is the piecemeal, under-resourced, single-method approach that has characterised too much of the response to gorse across New Zealand. A single spray without follow-up planting. Fire without revegetation. Mechanical clearing without herbicide. Biological control without active management. Each of these fails the seed bank test — and the seed bank always wins if it is not out-competed by native vegetation.

The Trust's model is built on this lesson. Drone-assisted herbicide application reaches terrain that has historically been untreatable. Coordinated multi-party programmes address the boundary fragmentation that has allowed re-invasion to undo individual landowner efforts. Immediate native planting closes the window the seed bank needs. And long-term monitoring catches the regrowth before it becomes a new infestation.

Wellington's gorse problem is large and entrenched. Solving it will take years, consistent investment, and genuine partnership across agencies, landowners, and communities. But it is solvable — and every hectare of gorse replaced by native forest is a permanent gain for biodiversity, for water quality, for fire safety, and for the communities that live in and around Wellington's hills.

The question is not whether gorse can be managed. It is whether we are willing to invest in doing it properly — with the right tools, in the right sequence, for long enough to let native vegetation take hold. That is what the Trust is here to do.