Entirely submerged, bottom-rooting, normally perennial. Slender rhizomes and roots. Stems 2-4 m long, branched, flat. Leaves alternate, oblong, thin, translucent, up to 80 x 15 mm, green to reddish-brown, with 3 main veins, often red, wavy at the margins (crimped in adult plants), with tiny serrations near tip. Flowers small, green, on spikes up to 1 cm long, Nov-Jan. 4 flat dark seeds.
Lakes, rivers, streams, drains.
Seed, rhizomes, stem fragments. Drains, aquaria. New catchments invaded by contaminated boats and trailers, eel nets, diggers, people ‘liberating’ fish, birds
Forms dense beds, shading out smaller native spp, preventing recruitment. Can contribute to blockage and flooding. Rotting vegetation stagnates water, killing fauna and flora.
Firstly establish that plant is not a valued native spp. Control is difficult, reseeding likely. In narrow waterbodies manipulate the plants growing conditions by reducing light, making it less competitive, eg plant trees to create shade.
1. Bottom lining: controls patches but reseeding may occur. Begin at upstream end of infestation and work down, 3-4 months per section.
2. Lower water level, mechanically remove or use weedmat.
3. Suction removal. Mulch. Generally not recommended in large still waterbodies as high chance of fragments spreading. If used, work methodically to trap all fragments, ensure collection bags do not leak. Water flow can assist to shift infestation boundary downstream.
4. Grass carp: requires consent, contact DoC.
Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.