Lagarosiphon

Also known as:
Oxygen Weed
Family:
Hydrocharitaceae
Origin:
South Africa

General description

Vigorous submerged perennial herb to <5m. Bottom-rooted oxygen weed common in garden ponds. Leaves recurved backwards or downwards, arranged spirally around the stem; leaves on other oxygen weeds are whorled. Tiny pink, solitary flowers.

Static or flowing freshwater to <6.5m deep: ponds, lakes, rivers, streams, dams. Widespread throughout NZ.

No seed set in NZ. Spread by stem fragments by water, boats, fishing gear, machinery.

Dense vegetation blocks dams & waterways impeding drainage, disrupting recreational activities. Out-competes native species. Serious threat to dune lakes & some threatened native species.

Site management

Almost impossible to kill, except in small patches. In narrow waterbodies, reduce light levels with riparian planting.

Recommended approaches

1. Handweeding by trained divers. Only suitable for small infestations.
2. Weedmat. Begin at upstream end of infestation.
3. Lower water level, mechanically remove, use weedmat where needed.
4. Suction removal generally not recommended in large still water bodies, high chance of fragments spreading. If used, trap all fragments, ensure collection bags do not leak. In moving water all sites below top of infestation are at risk; water flow can shift infestation boundary downstream.
5. Grass carp: requires consent, refer to DOC.

Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.

Similar species

egeria
Egeria densa

Egeria has its leaves arranged oppositely in whorls on the stem.

hydrilla
Hydrilla verticillata

Hydrilla has less leaves on a stalk and toothed leaf margins.

southern naiad
Najas guadalupensis

S naiad has toothed leaf margins and it's leaves are on short branches.

Search tags

RPMS status

Surveillance - Whole Region
National Pest Plant Accord species - nationwide
lagarosiphon - Main species image