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Parrot's feather (Myriophyllum aquaticum)

Parrot's feather forms dense mats that can block creeks, drains and channels and impede water flow. It can alter aquatic habitats, displace native water plants and disrupt waterway recreation and other activities.

Key facts

Type: Weed, aquatic.

Native to: Lowlands of central South America.

Established in: QLD, NSW, VIC, TAS, SA, WA.

Other names: Brazilian Water Milfoil, Brazilian Water-milfoil, Parrotfeather, Thread-of-life.

Identification

  • Look for a stout, blue-green or light-green aquatic herb with spreading, creeping or upright stems up to 2 m long.
  • The stems root freely at lower nodes and form tangled mats or masses.
  • Feathery leaves grow in rings around the stems; above-water leaves are crowded towards the stem tips.
  • Submerged leaves are usually larger than the above-water leaves and grow in rings of four to six.
  • Flowers are small and occur in the forks of upper emergent leaves; fruits and male flowers are not known in Australian populations.
  • Look-alike: Native water milfoils are the main plants to distinguish it from. Their emergent leaves are toothed rather than feather-like, and their feathery foliage occurs only below the water surface; parrot's feather has distinctive large, glaucous, feather-like leaves that persist above the surface.

Where it grows

In Australia it is widely naturalised in coastal districts of southern and eastern Australia, mainly on coastal plains from south-eastern Queensland to near Melbourne, with additional infestations in New South Wales, northern Victoria, Tasmania, South Australia and Western Australia.

Why it matters

  • Dense stands can block small creeks, drains and channels, impeding water flow.
  • Floating mats can interfere with irrigation, hydroelectric power production, transport, fisheries, recreation and tourism, and the plant can invade rice fields and affect crop yield.
  • The mats can reduce light, shade algae at the base of the aquatic food chain, and alter aquatic ecosystems.
  • Dense growth can displace native water plants and reduce natural biological diversity.

How it spreads

  • In Australia it reproduces vegetatively, as seed is not produced in Australian populations.
  • Brittle stems break into fragments through wave action, boats, mechanical harvesting and other activities; fragments move in stream flows and can root wherever they settle on sediments.
  • Ornamental plants can spread through nursery or personal trading and when aquarium contents are dumped into waterways.

Control options

  • Prevent introduction and spread, including further imports, because the establishment of male plants could allow seed production.
  • Mechanical cutting is usually ineffective because plants rapidly regrow from stem fragments; hand pulling, subsurface cutting and draglines may provide temporary control, but minimise fragment movement.
  • In small dams, covering the water with black plastic sheeting for several weeks has been used successfully.
  • Herbicides can be effective, but use only herbicides approved for aquatic environments and dispose of removed material carefully.

Hygiene and washdown

  • Avoid moving floating mats or stem fragments between waterways by boat or during mechanical work, as fragments can root wherever they settle.
  • 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): No national listing. Managed under state and territory law.
  • 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: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • 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: Declared pest (C3). C3 Management: landholders must manage it to reduce its impact and stop it spreading.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • 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.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources