What is the problem? 

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

What was the trial about? 

Living Water wanted to test the use of aerial spraying of the herbicide triclopyr (Garlon 360) with an UAV (drone) to reduce Ludwigia biomass. Watch a video of the drone in action. Note: triclopyr use around waterways is restricted, and permission is required to use it over water. Initial spraying was undertaken in early autumn 2019, with follow up in summer 2019 and summer 2021.

Who could use this information? 

DOC, regional and district councils, lake managers

What did Living Water learn from this project? 

Herbicide application was able to be highly targeted to areas of Ludwigia infestation. Triclopyr is a selective herbicide that is only effective on specific plant types. It is also effective for controlling willow (Salix sp.) so when further spraying was undertaken in subsequent years, the willows on the Lake margin were also sprayed. A large area can be sprayed in a comparatively short timeframe (hours), making aerial spraying much more cost effective than application by knapsack or drilling and poisoning willows. Spraying was very effective with almost full area reduction of Ludwigia, however ongoing control will be required to maintain low levels.