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Oxygen weed (Lagarosiphon major)

Lagarosiphon is not currently known to be established in Australia, but small infestations found here in the past were eradicated. If it becomes established, it can spread rapidly, form dense mats and be extremely difficult to eradicate.

Key facts

Type: Weed, aquatic.

Native to: Southern Africa and Madagascar.

Established in: .

Other names: Lagarosiphon, Oxygen plant, Oxygenating plant, Curly waterweed.

Best time to act: Growth is fastest in summer, and female flowers appear from summer until early autumn; report suspected plants as soon as they are found.

Identification

  • It is a perennial, submerged aquatic herb with brittle, sparsely branched stems that can grow to 5 m or more.
  • Numerous thread-like roots grow from stem joints, and rhizomes in the sediment anchor the plant to the bottom.
  • The stiff leaves are 5–20 mm long and 2–3 mm wide, and grow in alternate spirals along the stem.
  • Leaves usually have minutely toothed edges and tapered tips that curve strongly down towards the stem.
  • Female flowers are tiny, solitary and white to pinkish; male flowers break off and float to the surface.
  • Look-alike: Canadian pondweed, Hydrilla and Egeria are similar submerged water weeds found in Australia. Lagarosiphon has leaves arranged in alternate spirals along the stem, while these lookalikes have leaves in whorls around it.

Where it grows

There are no naturalised infestations currently known in Australia; small infestations near Melbourne and Newcastle were eradicated in the late 1970s.

Why it matters

  • Dense growth can dominate lakes, dams and slow-moving streams, forming thick mats that block light and displace native vegetation.
  • Dense infestations can deplete oxygen in the water and restrict habitat for native fish, waterbirds and other fauna.
  • Infestations can choke waterways, reduce opportunities for recreation and block water intakes, including those used for hydro-electricity.
  • Long stems can block water-pumping equipment and affect the propellers and cooling systems of recreational equipment.

How it spreads

  • It spreads by vegetative reproduction, as rhizomes take root and produce new growth.
  • Fragments can break off naturally or be dislodged by fast-flowing water or disturbance; roots grow from fragment joints and form new plants.
  • Fragments are frequently transported on boats and trailers, and infestations in New Zealand are often first recorded at boat ramps.

Control options

  • Prevention, early detection and eradication are important. Report suspected plants immediately to a local council or state or territory weed management agency, and do not attempt control without expert assistance.
  • Manual removal and mechanical harvesting are unreliable because fragments left behind can regrow; poorly performed or incomplete control can spread the weed.
  • Burial is the quickest stated disposal method; sun-drying or burning are also suitable if there is no risk of spreading fragments into a waterway. Steam exposure for about 30 seconds after removal from water was found to be extremely effective at killing plants.
  • No environmentally acceptable systemic herbicide that targets the rhizomes is known; the herbicide considered environmentally acceptable in New Zealand does not kill rhizomes, so regrowth is inevitable. Use only registered herbicides and approved methods.

Hygiene and washdown

  • Fragments can be carried on boats and trailers, so check them for plant material before moving between waterways and prevent fragments from entering the water.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): National priority exotic pest. On the National Priority List of Exotic Environmental Pests, Weeds and Diseases, so any new detection should be reported straight away. National Environmental Alert List. One of 28 weeds named on the National Environmental Alert List as early-stage invaders with serious potential to harm the environment.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • Victoria: State prohibited weed. State prohibited weeds are the highest priority: the Victorian Government is responsible for eradicating them, so report any sighting to Agriculture Victoria.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • Australian Capital Territory: Declared pest, notifiable, prohibited. It is a declared pest throughout the ACT. You must report it to ACT Biosecurity. Dealing with it, such as selling, moving or keeping it, is prohibited.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

Sources