Giant Arrowhead

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

General description

Marginal emergent perennial herb <2m from creeping rhizomes. Young emergent leaves narrowly arrow shaped <15cm long; submerged leaves long strap-like; mature leaves arrow shaped <40cm long. White flowers (Nov-Apr) with a purple patch in centre in whorls on round smooth erect stems. Other Sagittaria species have triangular, creeping stems, and longer leaves.

Static or slow flowing shallow waterways <50cm deep: drains, streams, pond margins.

Spreads locally from seed & creeping roots. Seeds & rhizome fragments by water, machinery, wildlife, humans.

Restricts water movement, increases sedimentation, aggravates flooding. Displaces native plants in wetlands.

Site management

Regular follow up required. Clean all boats, trailers fishing gear etc. Plant tall trees to shade site. Check downstream.

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.

Similar species

arum lily
Zantedeschia aethiopica

Arum lily is more common. It is a much larger plant with larger leaves with a distinctive mid vein. Terrestrial to marginal habitat

elephants ear
Alocasia brisbanensis

Elephants ear is more common. It is a much larger plant with larger leaves with a distinctive mid vein. It contains a milky sap. Terrestrial habitat.

RPMS status

Total Control - Whole Region
giant arrowhead - Main species image