Tech tool used to target pest plants at precious wetland

Source: NZ Department of Conservation

Date:  12 March 2026

Whangamarino is 7000 ha wetland an hour north of Hamilton, comprising open water, swamp, fen and peat bogs. It is listed as significant under the international Ramsar Convention on Wetlands and is home to numerous threatened plant and insect species.

A recent report on the wetland to the Convention identifies a concerning decline in water quality, indigenous wetland habitat, the wetland’s Australasian bittern/matuku population, and cultural values recognised by mana whenua.

One of the biggest threats to Whangamarino is invasive weeds, which outcompete native plants and alter the waterways and food sources essential to taonga species.

Royal fern is among those. It’s an introduced, tough and adaptable deciduous plant, which grows rapidly and can take over wetlands by crowding out slower-growing, rare native species found in Whangamarino.

Department of Conservation Biodiversity Ranger Lizzie Sharp says two drones, operated by specialist pilots, were used to map the royal fern and implement targeted herbicide control during fine weather periods in late February.

“Slogging through the peat bog to carry out ground control would be very hard going for our teams and could also risk damaging the surface of the bog,” Lizzie says.

“The drones took to the air and used a targeted jet of herbicide on the royal fern in the centre of the bog, before moving out toward the edge of the bog in an effort to push the invasion back.”

It’s the first time royal fern has been controlled using an aerial device, and the success and efficiency of the method may lead to it being used to control other weeds in future. The contractors carried out half a day of mapping their work area before three days of control using the drone.

Lizzie says with weather increasingly unpredictable due to climate change, numerous approaches to pest plant control will be needed – and drones will be valuable for protecting important habitats like Whangamarino.

Left uncontrolled, royal fern will appear in most habitats, especially bare damp ground. It produces thousands of spores distributed by the wind and unintentional human carriers and forms dense forests shading out all other species. At Whangamarino, this includes native peat bog vegetation which has adapted to exposed sunlight. After the fire of October 2024, royal fern has used the disturbed ground to grow into dense canopies at a faster pace than native plant species.

Lizzie says contractors used a helicopter to control willow species across the wetland during summer. Willow is another introduced pest plant which can cover the breeding and feeding habitat for matuku-hurepo/Australasian bittern. The helicopter method was similar to the use of the drone, with half a boom used to apply herbicide to the willows. Precision spot-spraying on individual trees complements aerial control and means surrounding vegetation is not impacted.

Willows also absorb water from the surrounding area. Their root systems create mounds of earth where water should be running, altering fish populations. Whangamarino locations where willows were controlled a few years ago have native plants returning to support insects, fish and birds in the area.

The aerial application of herbicides is strictly controlled through DOC’s operating procedures and a set of rules and regulations that DOC and its contractors must follow.

Whangamarino is precious and fragile eco-system, and as it recovers from the fire of 2024, people are asked not to go naturing in the wetland to protect the fragile peat bog.

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