Stout, hairless, freshwater perennial. Sprawling mats in water or carpets of short growth on semi-exposed banks. Submerged stems yellow-green, emerge 10cm above water. Stems <2m in still water and <4m in flowing water; fibrous roots at each node. Emergent leaves in whorls 4-6, densely packed at stem ends, bright blue-green, deeply divided, feathery. Small single flowers have no petals.
Still or flowing freshwater, rooting either above or <2m below water surface. Prefers nitrogen-rich water, temperatures 8-30ºC; tolerates occasional frosts, some salinity.
No seed set in NZ. Spread by stem fragments carried by water, boats, fishing gear, machinery.
Traps sediment, infills shallow waterways, impedes drainage, causes flooding, disrupts recreational activities, out-competes native water plants.
Very difficult to control in deep water. Stem fragments resprout. In narrow waterbodies, reduce light levels with riparian planting.
1. Rake up and dispose, follow up. Spray marginal regrowth.
2. Weed mat small areas, 3-4 months. Start at top of infestation.
3. Lower water level, mechanically remove, use weedmat or dry out thoroughly for 2-3 weeks.
4. Suction removal generally not recommended in large still waterbodies, high chance of fragments spreading. If used, trap all fragments. In moving water all sites below top of infestation are at risk.
5. Spray emergent vegetation including banks <500mm above present water level Oct- Nov (100ml glyphosate/10L, use glyphosate formulation approved for use over water). Respray before growth reaches 50mm high, approximately 3-5 weeks apart. Respray Jan-Feb. Monthly checks over winter to pick up regrowth.
Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.