Council to launch trial programme to control invasive water weed

In April/May this year, Nelson City Council will start a trial programme to control invasive water celery (Apium nodiflorum also known as Heloscadium nodiflorum) in Orphanage Stream, Stoke using an approved herbicide that doesn’t persist in the environment.

Water celery is native to Europe, northern Africa and western Asia. In New Zealand it has spread through the North Island and is now becoming established in the Nelson region. It is a bright green spreading plant that grows easily from seed and from pieces of root detached from the main plant.

Water celery infestation can affect infrastructure and native habitats. A stream choked with water celery can increase the size and frequency of flood events, and it forms dense mats that block sunlight and de-oxygenate the water, smothering our local flora, trapping sediment and reducing habitat for stream life.
There are records of a variety of threatened and at risk native fish in Orphanage Stream,  including longfin eels; giant kokopu; torrentfish; shortjaw; lamprey; koaro; inanga; bluegill; and redfin bully.

Contractors will be using the selective herbicide Triclopyr triethylamine (Garlon 360) - which degrades in water and soil and only targets specific species. It also has low toxicity to fish and other stream life. It is recommended by NIWA for the effective control of this weed in our waterways and the Council has been granted permission to use it by the Environmental Protection Authority.

 Council will be monitoring the stream before, during and after spraying for adverse effects on pH, dissolved oxygen and temperature. Once the weed mass has died off, it will break up and slowly wash downstream.

Please look out for signage around the worksite and follow all instructions. Do not collect any plants within the area being sprayed, and keep dogs and children away from the work area.