Red ludwigia (Ludwigia repens)

Red ludwigia is a creeping aquatic plant with red stems. It can dominate waterways and outcompete native plants.

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How does this weed affect you?

Red ludwigia can form dense infestations that can:

• cause sediment to build up and restrict water flow or cause flooding
• outcompete native plants
• reduce light, food and habitat for fish and other aquatic animals
• reduce water quality especially by reducing oxygen levels
• limit recreational activities such as swimming and boating on waterways.

What does it look like?

Red ludwigia is a perennial water weed. It has branched stems that spread over banks of waterways and can float in the water.

Leaves are:

• green (sometimes with a reddish tinge) on top
• reddish-purple underneath
• up to 4.5 cm long and 2.7 cm wide
• roundish or spear-shaped, thinner at the base
• on stalks up to 2.5 cm long
• opposite on the stem.

Flowers:

• have 4 yellow petals 1–3 mm long
• have prominent 4 triangular sepals (leaf-like structures) up to 5 mm long
• are in pairs in the leaf forks
• are present in summer and autumn.

Fruit are:

• a capsule
• 5–10 mm long and about 2.5 mm wide
• oblong with rounded corners.

Seeds are:

• yellowish-brown
• in several rows within the fruit capsule.

Stems are:

• reddish
• floating or ascending 
• hairless
• branched with roots at the nodes.

Similar looking plants

Red Ludwigia looks similar to:

• The native water primrose (Ludwigia peploides subsp. montevidensis) which has alternate leaves and larger flowers with petals up to 2 cm long.
• The introduced marsh ludwigia (Ludwigia palustris) which has alternate leaves and flowers without petals.

Where is it found?

This weed has been found growing along the Lane Cove River in Sydney and on the North Coast of NSW.

It is native to the USA, Mexico and the Caribbean.

What type of environment does it grow in?

Red ludwigia grows in shallow water and along the edges of waterways. It grows best in slightly acidic waters and prefers 19-28°C.

How does it spread?

Red ludwigia is an ornamental pond and aquarium plant that could be spread by people dumping plants near waterways

By seed

Seeds can be spread by moving water including flood water and in contaminated mud that can attach to animals (especially water birds), clothing footwear or machinery.

By plant parts

New plants can grow from stem fragments, which can be moved by moved by water, boats or machinery.

References

Champion, P.D., Burnett, D.A. and Petroeschevsky, A. (2008). Risk assessment of tradeable aquatic plant species in Australia. Prepared for NSW Department of Primary Industries. National Institute of Water and Atmospheric Research, O’Connor, Western Australia.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 16 June 2021 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ludwigia~repens

Technigro (2012). Weed Watch, Your alert to new and emerging threats: Red Ludwigia (Ludwigia repens) Retrieved 18 July 2021 from: http://www.technigro.com.au/wp-content/uploads/2016/10/45-Red-Ludwigia.pdf

Uddin, M. E., Islam, A. M. T., Chowdhury, M. A. U., Rahman, M. K., Islam, M. S., & Islam, M. R. (2012). Sedative and analgesic activities of Ludwigia repens. Phytopharmacology, 2(2), 202-211.

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 seedlings. Using a combination of control methods is usually more successful.

Prevention

Never dump aquatic plants in waterways.

To help prevent the spread of red ludwigia 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 red ludwigia.

Physical removal

By hand

Pull out individual plants or small infestations by hand. Make sure that no stem or root parts remain. Dispose of all the plant parts.

Disposal

Contact your local council for advice on how to dispose of this weed.

Chemical control

Spot spray actively growing plants. Only herbicide products that have label approvals in place for aquatic use can be used in aquatic situations.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 50 parts water
Comments: Spot spray
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 9 parts water
Comments: Splatter gun
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
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.

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Reviewed 2021