Leafy elodea (Egeria densa)

Also known as: dense waterweed, Egeria

Leafy elodea is an underwater weed except for its white flowers that grow at the water’s surface. It forms dense mats that reduce habitat for fish and make recreational activities difficult.

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How does this weed affect you?

Leafy elodea forms dense mats beneath the water surface that:

• restrict water flows
• increase silting
• outcompete native plants
• reduce food and shelter for fish and other native aquatic animals
• can block irrigation equipment, domestic pumps and hydroelectric systems.
• make swimming, boating and fishing difficult.

What does it look like?

Leafy elodea is a perennial plant which grows beneath the water’s surface. It is usually rooted in the mud, however it may also be free floating within the water.

Leaves are:

• 10–40 mm long and 2–5 mm wide
• strap-like and tapered to a point which often curves backwards
• in whorls of 3–8, usually more on the upper parts of the stem
• very finely toothed along the leaf margins, only visible by a hand lens
• mostly below the water surface but can reach the surface.

Flowers:

Male and female flowers grow on separate plants but only male flowers have been found in Australia. The male flowers are:

• white with yellow centres
• 1.2–2.5 cm wide with 3 petals, 6–8 mm long
• at the water surface
• on stems up to 8 cm long
• present in spring-autumn.

Fruit are:

• not present in Australia
• cylindrical berries
• 7–8 mm long and about 3 mm in diameter.

Stems are:

• green or brown
• up to 5 m long and 2.0–2.5 cm in diameter
• cylindrical
• upright, underwater for most of their length.

Similar looking plants

Leafy elodea’s most distinctive features are its very crowded leaves and relatively large, showy white flowers. It looks similar to:

• Elodea (Elodea canadensis) which has shorter leaves that are spaced more widely and smaller flowers.
• Lagarosiphon (Lagarosiphon major) which has downward curling leaves that are not grouped in whorls and spiral around the stem.
• Hydrilla (Hydrilla verticillata), a native plant, with distinctly serrated leaves in whorls that are more widely spaced up the stem. It also has smaller less conspicuous flowers.

Where is it found?

Leafy elodea has been found in coastal regions of NSW from Greater Sydney to the North Coast. Infestations have also been found in the Central West, Riverina and Murray Regions. It is also found in south-east Queensland.

 It is native to parts of South America.

What type of environment does it grow in?

Leafy elodea grows in warm temperate, subtropical and tropical regions though it is more cold tolerant than many other aquatic weeds. It has been found in slow-moving or still water up to 7 m deep including ponds, lakes and slow moving streams and rivers. 

It grows best in nutrient-rich conditions, though it tolerates a wide range of nutrient levels. It prefers areas where the sediment has been disturbed.

Leafy elodea can tolerate very low light levels caused by either shade or sediment in the water.

Maps and records

• Recorded presence of Leafy elodea during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  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

Leafy elodea can spread from plant fragments. Pieces of stem break from the main plant easily especially in autumn. Boat wash and mechanical harvesting can cause more pieces to break up. Fragments are spread by flowing water especially floods. They can survive out of water and be spread caught on boat trailers, fish traps or other equipment.

Leafy elodea was once used in aquariums, and plants have been spread by people dumping plants.

By seed

Leafy elodea is not known to produce seed in Australia.

References

Grantley, J., McPherson, F., & Petroeschevsky, A. (2009). Recognising water weeds: plant identification guide. Industry & Investment NSW.

Parsons, W. T. and Cuthbertson, E. G. (2001) Noxious Weeds of Australia. 2nd Edition. CSIRO Publishing, Collingwood. pp. 61–63.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 21 July 2021 from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Egeria~densa

Sainty, G. R. Jacobs, S. W. L. (2003) Waterplants in Australia. 4th edition. Sainty and Associates, Potts Point. pp. 84–85.

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means looking for and killing regrowth or new infestations. Using a combination of control methods is usually more successful.

Contact your local council weeds officer for advice on controlling leafy elodea.

Prevention

Never dump aquatic plants in waterways.

To help prevent the spread of leafy elodea when fishing or using waterways for other recreational activities:

• avoid running motors or paddling through water plants
• check your boat/watercraft, trailer and equipment for plant material before you leave a site and before launching at a new site
• remember to check the inside of boats, live wells, bilge and bait containers
• remove all plant material that you find before you leave a site and before launching at a new site
• contact your local council if you think you have seen leafy elodea.

Disposal

Remove this plant from aquariums and garden ponds. Contact your local council for advice on how to dispose of this weed. Drying in the sun followed by burying or burning plants can be an effective way to dispose plants.

Physical removal

Mechanical harvesting can reduce the bulk of the species but plants usually resprout. Often more plant fragments are produced and these spread further downstream. Cutting, hand pulling and mechanical harvesting can all cause further spread. 

Chemical control

Tablets

When using Clipper herbicide tablets, control is directly related to the amount of sunlight on the water body. Sunny warm conditions give best control. Weeds growing in shaded areas may require additional applications. A permit is required to use clipper herbicide tablets.

Spraying and injection

Only use herbicides registered for aquatic use. Read label thoroughly and follow label requirements including withholding periods.

Herbicide options

See Using herbicides for more information.

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Diquat 200 g/L (Reglone®)
Rate: 5 L /megalitre water
Comments: Apply by injection below the surface or as a surface spray.
Withholding period: Do not use treated water for human consumption, livestock watering or irrigation purposes for 10 days after application. Do not graze or cut sprayed vegetation for stock food for 1 day after application. See label for harvest withholding periods.
Herbicide group: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: 1 tablet for every 37.5 cubic metres of water to achieve 400 parts per billion.
Comments: For use on dense or established weed populations in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger, still water bodies. Throw tablets directly into the water to achieve uniform distribution of the herbicide. See label for further instructions and restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Inject solution into water body. 1 tablet per 37.5 cubic metres. Each tablet dissolved in at least 20L of water + 0.5-1.0% adjuvant/surfactant
Comments: For use on dense or established weeds in water bodies less than 0.5 m deep or with a volume less than 37.5 cubic metres. Dissolve tablets in water (at least 20 L per tablet) mix thoroughly and then inject the solution directly into the water body.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
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 pest 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.
North West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2023