Arrowhead

Also known as:
Hawaii Arrowhead
Family:
Alismataceae
Origin:
North & South America

General description

Perennial herb with creeping stems. Large, glossy, narrow arrow-like leaves above the water on triangular stalks. Flowers (Oct-Apr) 3 petals, white with purple blotch at base. Longer leaves and triangular stems distinguish it from S. montevidensis.

Static or slow moving shallow fresh water: drains, streams, pond margins. Not yet known in NZ. Possible sightings should be reported immediately.

Spreads locally from creeping root system, tubers, stem fragments. Also spread by dumping.

Same as S. montevidensis.

Site management

Difficult to physically control due to presence of tubers and propagules. Follow up at least 6-monthly until site clear. Check downstream. Plant tall trees adjacent to shade site

Recommended approaches

1. Report it immediately to the Auckland Council Biosecurity team, who will arrange for its control at their expense.
2. Weedmat: Start at top of infestation, leave 3-4 months.
3. Lower water level, mechanically remove, apply weedmat.
4. Stem inject (5ml undiluted glyphosate) into base of each stem.
5. Weed wipe (300ml glyphosate + 2ml penetrant/1L).
6. Spray terrestrial sites spring - autumn (100ml glyphosate + 20ml penetrant/10L)
7. Spray aquatic sites (100ml 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.

RPMS status

Total Control - Whole Region
arrowhead - Main species image