Erect, perennial herb <3m tall. Square stems, smooth or hairy. Stalkless leaves that grow either opposite or in whorls from the stem, heart-shaped at base but lance-shaped overall. Numerous magenta flower spikes (Dec-Feb). Mature plants produce <660,000 seeds per year.
Wetlands, drains, riparian areas, lake margins, ditches, streams, drier open areas. Tolerates a wide range of environmental conditions.
Prolific seeder, seeds spread mainly by water. Vegetative spread by underground stems and stem fragments.
Highly aggressive invader of natural and disturbed wetlands. Major pest in North America, capable of taking over million of hectares of wetlands. Impedes waterfowl, prevents access to waterfowl and recreational users, out-competes native vegetation, decreasing overall species diversity.
Plant shady trees adjacent to infested margins. Implement control at margins to prevent seeding. Progressively eliminate infestations, working downstream where possible. Deepen water to prevent growth where possible.
1. Report it immediately to the Auckland Council Biosecurity team, who will arrange for its control at their expense.
2. Weedmat for 3-4 months, start at top of infestation.
3. Spray sites next to or on waterbodies, respray until eradicated (100ml glyphosate/10L, use glyphosate formulation approved for use over water).
4. Terrestrial sites – slash large plants to ground level & spray regrowth once it reaches 50cm tall. This will minimise non target damage (60ml Tordon BK/10L or 30ml triclopyr/L/10L, follow up 3-monthly).
Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.