Eurasian water milfoil (Myriophyllum spicatum)

PROHIBITED MATTER: If you see this plant report it. Call the NSW DPI Biosecurity Helpline 1800 680 244

Eurasian water milfoil is an underwater weed with olive-green feathery leaves. It can quickly take over waterways.

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How does this weed affect you?

Eurasian water milfoil grows quickly and:

  • shades out and displaces native water plants
  • reduces food and habitat for native fish and other aquatic animals
  • interferes with irrigation water flows
  • impedes fishing and boating. 

What does it look like?

Leaves are:

  • olive-green
  • less than 4 cm long
  • feather-like
  • usually submerged
  • in whorls of four around the stem

Each leaf is divided into 5–25 pairs (usually more than 12) of leaflets. 

Flowers are:

  • held above the water in an upright spike 5–20 cm long
  • in whorls of 4 around the spike.

Male flowers are:

  • in whorls above the female flowers
  • 3 mm long with pink petals.

Female flowers:

  • are 2–3 mm long
  • don’t have petals.

Fruit are:

  • 2–3 mm long
  • red
  • round with 4 smooth sections divided by wrinkled ridges
  • on spikes that are above the water surface but lie parallel to the water rather than upwards when it is flowering.  

Stems are:

  • red-brown to white-pink 
  • up to 7 m long and about 5 mm in diameter 
  • hairless 
  • branched near the surface to form a dense canopy.

Where is it found?

Eurasian water milfoil does not currently grow in Australia. If introduced, it could become a major weed of dams, lakes and reservoirs.

Eurasian water milfoil is native to Europe, Asia and northern Africa.

It is now naturalised and a major weed of lakes and reservoirs in Canada and the USA. 

What type of environment does it grow in?

Eurasian water milfoil:

  • can grow from a depth of 10 m but usually grows in water up to 3 m deep
  • thrives in a range of temperatures and water conditions including low salinity
  • prefers slow or still water in lakes, ponds and shallow reservoirs
  • will also grow in fast-moving water. 

Maps and records

  • Recorded presence of Eurasian water milfoil during property inspections (Map: Biosecurity Information System - Weeds, 2017-2020)
    These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.

How does it spread?

By plant parts

Plants break apart as they grow. They often develop roots before they separate from the parent plant. Water movement and human activities can also break plants into fragments. Fragments can be spread long distances by water currents. This weed is mainly spread between water bodies by boating and fishing activities.

By Seed

Eurasian water milfoil can reproduce by seed, but the seeds rarely germinate. The seeds can remain dormant for many years. Water birds move the seeds.

References

Aiken S.G., Newroth P.R. and Wile I. (1979) The biology of Canadian weeds, 34. Myriophyllum spicatum L., Canadian Journal of Plant Science, 59: 201–215.

Hosking J.R., Sainty G., Jacobs S., and Dellow J (in prep.), The Australian WEEDbook.

More information

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Control

Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately.

NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading

Control of Eurasian water milfoil is difficult. Mechanical harvesting can lead to rapid reinfestation due to the plant being fragmented.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


Dichlobenil 40 g/kg (Casoron 4G Herbicide)
Rate: 2.9 to 3.9 kg per 10m2
Comments: Exposed soil. DO NOT apply to water which will be used for crop irrigation, for livestock watering, or for human consumption.
Withholding period: Do not graze livestock on treated areas.
Herbicide group: O, Inhibitors of cell wall (cellulose) synthesis
Resistance risk: Moderate


Dichlobenil 40 g/kg (Casoron 4G Herbicide)
Rate: 287 to 388 kg per ha or 2.87 to 3.88 kg per 100m2
Comments: Water less than 1m deep. Apply when weeds are dormant. DO NOT apply to water which will be used for crop irrigation, for livestock watering, or for human consumption.
Withholding period: Do not graze livestock on treated areas.
Herbicide group: O, Inhibitors of cell wall (cellulose) synthesis
Resistance risk: Moderate


Dichlobenil 40 g/kg (Casoron 4G Herbicide)
Rate: 388 to 574 kg per ha or 3.88 to 5.74 kg per 100m2
Comments: Water more than 1 m deep. Apply when weeds are dormant. DO NOT apply to water which will be used for crop irrigation, for livestock watering, or for human consumption.
Withholding period: Do not graze livestock on treated areas.
Herbicide group: O, Inhibitors of cell wall (cellulose) synthesis
Resistance risk: Moderate


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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area Duty
All of NSW General Biosecurity Duty
All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW Prohibited Matter
A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2020