Hardy, semi-aquatic, perennial herb <1.5m high, grows <15cm/week in fertile conditions. Young stems angled; rounded, hollow on maturity, forming floating mats. Dark green, opposite leaves shiny, hairless, ovate – lanceolate, serrated wavy edges. White flowers (Nov-Apr) in ball-like clusters. Roots finely fibrous, root from aerial stem nodes. Dormant during winter.
Marshy soils, still or flowing water: wetlands, streams. Prefers warm fertile climate, tolerates frost.
Seeds spread via water, animals, machinery. Stem fragments spread by water, machinery.
Mats quickly cover waterways, impeding drainage, disrupting recreational activities, choking hydro turbines. Out-competes native species.
Follow up 3-monthly until eliminated. Do not graze, as stock will release fragments.
1. Report it immediately to the Auckland Council Biosecurity team, who will arrange for its control at their expense.
2. Dig out small infestations by hand, removing all stems and roots.
3. Weed wipe spring-summer, (500ml glyphosate + 2ml penetrant/1L).
4. Spray terrestrial sites spring-summer (200ml glyphosate + 20ml penetrant/10L).
5. Spray aquatic sites spring-summer (200ml glyphosate/10L, use glyphosate formulation approved for use over water).
Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.