Lake Ruatuna before Ludwigia control

Water Primrose (Ludwigia) Control

Fish Habitat – With Descriptor

About the project

Water Primrose (Ludwigia peploides subsp. montevidensis) is an introduced sprawling emergent aquatic plant species which can grow rapidly and smother other aquatic vegetation.

Over the last couple of years, Ludwigia growth at Lake Ruatuna has been steadily increasing. At the height of the 2018-19 summer it covered around 2.9 ha the lake surface and surrounding waterways, reaching nuisance levels and preventing effective drainage into the lake.

Overseas, Ludwigia has been controlled by hand weeding, excavation and use of chemical herbicides.

This project aims to reduce Ludwigia biomass through aerial spray of the herbicide triclopyr (Garlon 360) using an UAV (drone). Watch a video of the drone in action.

Note: triclopyr use around waterways in New Zealand is restricted, permission is required to use it over water is required.


  • Targeted application of herbicide to areas of Ludwigia infestation
  • A large area can be sprayed in a comparatively short timeframe (hours)
  • Triclopyr is a selective herbicide that is only effective on specific plant types. It is also effective for controlling willow (Salix sp.) so be used to achieve multiple control objectives



  • Initial spraying was undertaken in early autumn 2019
  • A total area of 2.1 ha was sprayed using an UAV
  • Successful results with almost full area reduction of Ludwigia
  • Further spraying of areas of Ludwigia combined with willows will be undertaken in summer 2019-20

Ludwigia control progress

Began 2019, estimated completion 2020

Progress: 50%

Lake Ruatuna after the Ludwigia control