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Eurasian water milfoil (Myriophyllum spicatum)

It is present in Australia but is not known to be naturalised here. If it escapes from aquaria or ponds, it could become a serious weed of lakes, dams and reservoirs and threaten certain habitats.

Key facts

Type: Weed, aquatic.

Native to: Europe, Asia and northern Africa.

Established in: VIC.

Other names: Eurasian Water-milfoil, Eurasian Watermilfoil, Spiked Water Milfoil.

Best time to act: Growth is most prolific in summer, and flowering is most likely in late summer and early autumn.

Identification

  • This is a mostly submerged, rooted perennial aquatic herb with hairless, reddish-brown to whitish-pink stems that can grow 7 m or more long.
  • Stems are generally branched near the water surface, forming a dense canopy, and become leafless towards the base.
  • Stiff, feathery greyish-green or olive-green leaves grow in rings of three or four around the stem; each has 14 to 24 pairs of fine segments.
  • When flowering, narrow spikes up to 8 cm long rise above the water, with small flowers arranged in rings.
  • Look-alike: Parrot's Feather has glaucous blue-green leaves on shoots that emerge above the water, while Eurasian Water Milfoil's leaves are more finely divided and all submerged.
  • Look-alike: Native Watermilfoil has undivided reddish-purple emergent leaves, while Hornwort has narrowly branched or forked leaves rather than comb-like, feathery leaves.

Where it grows

In Australia it is present but not known to be naturalised in any state or territory; it was introduced as an ornamental for aquaria and ponds.

Why it matters

  • Dense stands can choke water bodies, shade out other species and alter the water's temperature profile.
  • Overseas, infestations have reduced invertebrate diversity and fish numbers and interfered with irrigation, boating, fishing, swimming and other water uses.
  • In Australia it is considered a potential weed and a serious threat to certain habitats.

How it spreads

  • It spreads mainly through human activity, including the trade in aquatic plants for aquaria and ponds.
  • Stem pieces are the main means of vegetative spread; spread by seed is less common.
  • Moving water and activities such as boating can disperse fragments, and water birds may also spread it.

Control options

  • Mechanical harvesting can lead to rapid reinfestation because the plants fragment.
  • Periodic lowering and raising of water levels can reduce aquatic weed growth.
  • Use only herbicides approved for aquatic environments; regrowth can be fast, so repeated control may be necessary if plants are not killed.
  • Water-level changes and herbicide treatments require caution to avoid harming desirable species and native habitats.

Hygiene and washdown

  • Stem fragments can be dispersed by boating and moving water, so check boats and gear for plant pieces before moving between water bodies.
  • 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: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with it. 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: 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 (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • 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: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

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.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria

Sources