A successful trial was recently held to assess the feasibility of using drones to spray invasive pampas grass on Te Hauturu-o-Toi / Little Barrier Island. The five-day trial, funded by a grant from the Chisholm Whitney Charitable Trust, aimed to evaluate the viability of using a drone. Its objectives were to: Compare the drone’s effectiveness and efficiency against traditional methods such as helicopter and ground teams Minimise the need for human landing and equipment transport onto the island Reduce overall herbicide usage through improved spraying precision The trial involved launching the drone directly from a DOC boat offshore. That wasn’t always easy due to variable weather conditions with winds, heavy swells, backwash and glare making the job difficult at times. Occasional GPS loss also caused some temporary issues. The drone, which climbed up to 188 feet (57.3 m), was used to access a wide range of area such as vertical faces, regenerating slips as well as more technical sites such as in between large pōhutukawa trees and cliff faces. Recent flights by Island Solutions have exceeded 130 m. All of those locations were inaccessible to helicopters due to tight space and to abseilers because of frequent rock falls. What’s more, the ability to apply selective herbicide with high accuracy reduced overall chemical use and harm to non-target species. The large droplet size and horizontal spray lance enabled effective application even in windy conditions. One of Hauturu’s DOC rangers, Richard Walle, was pleased with how the trial went, saying effective invasive weed control is an essential element in protecting the integrity of the island’s ecosystem. “Despite some challenges, the drone spray trial was a great success, saving many hours of difficult abseiling work and sharply reducing helicopter fuel use and associated emissions. We were particularly impressed by the drone’s precision, which allowed us to target invasive pampas while minimising impacts on the surrounding ecosystem.” Hauturu Supporters Trust Chairperson Ed Chignell adds: “We are very pleased with how the drone trial went and would like to see more weed control done with drones rather than abseiling, which is dangerous for rangers and professional weeders.” Plans are being made for follow-ups, which will be necessary for completely eradicating all of the sprayed plants and preventing re-seeding. Another wind-dispersed invasive pest – Mexican devil weed – has been identified as another good candidate for future spraying projects. Using the drone allowed for high-precision spraying that minimised spray drift and greatly reduced non-target species being affected. The lighter patches on this cliff shows a range of sites reached by the drone. The trial used Haloxyfop grass-selective herbicide with a vegetable oil-based surfactant. Photos Island Solutions. Spraying stats Total flights: 42 of varied duration between 5 and 12.5 minutes Total herbicide used: 4.1 L Estimated controlled plants: 159 adults, 197 juveniles, millions of seeds.
