Also known as
Where is it originally from?
What does it look like?
Erect perennial herb (<1m tall) with creeping rhizomes and square stems. Mint-like leaves (3 x 8.5cm) are dark green, opposite, deeply toothed and prominently veined, but don’t have a mint smell. Tiny white to pale pink/purple flowers (Dec-Mar) are clustered where leaves join stems, and form minute seeds (nutlets).
Why is it weedy?
Seeds are highly buoyant and can be dispersed by water. They can germinate after floating for 15 months and can also be spread by machinery, footwear and stock. Grows rapidly and densely. Some salinity tolerance and some shade tolerance, making it able to invade established native vegetation along river banks and lake margins.
How does it spread?
Buoyant seeds and creeping stolons.
What damage does it do?
Can dominate the margins of still water bodies and can invade native vegetation in these areas, such as stands of raupo.
Which habitats is it likely to invade?
Occurs in the margins of lakes, rivers, ponds and other water bodies, in drainage ditches, damp pasture and waste land.
What can I do to get rid of it?
1. Weed wipe (during active growth): (50ml glyphosate/L).
2. Overall spray: terrestrial sites (100ml glyphosate + 20ml penetrant per 10L), or aquatic sites (100ml glyphosate/10L, use glyphosate formulation approved for use over water).
What can I do to stop it coming back?
Replant area with native species to prevent re-establishment. Follow up for rhizome regrowth.