Long-leaf willow primrose (Ludwigia longifolia)

Long-leaf willow primrose is an aquatic shrub with yellow flowers. It forms dense stands in slow-moving or still water.

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How does this weed affect you?

Long-leaf willow primrose is an aquatic weed that could invade large areas of NSW waterways and wetlands. It forms dense colonies in slow moving and static waterways. It:

• outcompetes native plants
• reduces food and habitat for fish and other aquatic animals
• changes water flow and increases flood risks
• limits access to waterways.

What does it look like?

Long-leaf willow primrose is an upright annual shrub up to 3 m tall that grows in wet areas and in water.

Leaves are:

• long and thin with a pointed tip
• 10–20 cm long and 0.5–2.5 cm wide
• larger lower down and smaller higher up the stem
• stalkless
• alternate on the stems.

Flowers are:

• yellow with 4 (or rarely 5) petals each 2.0–2.5 cm long and 4 red or green sepals
• single in the junctions of upper leaves
• present from summer–winter.

Seedpods are:

• 1-4 cm long and 4–8 mm wide
• oblong to narrow-oblong
• 4-angled with lots of seeds in separate chambers.

Seeds are:

• brown to yellow
• less than 1 mm long
• abundant and dust-like.

Stems are:

• red or greenish
• narrow and square shaped often with winged edges
• usually branching towards the top.

Roots are:

• shallow
• fibrous.

Similar looking plants

Long-leaf willow primrose looks like other Ludwigia species:

• Willow primrose (Ludwigia octovalvis), a native species, which has hairy stems, leaves and fruit and almost round stems.
• Water primrose (Ludwigia peploides subsp. montevidensis), a native species, which has a creeping habit and small leaves up to 6 cm long.
• Peruvian water primrose (Ludwigia peruviana), an introduced weedy species, which has hairy stems, leaves and fruit with shorter, broader leaves.

Where is it found?

Long-leaf willow primrose grows on the NSW coast and in some inland areas. Most infestations in NSW are in the Greater Sydney and Hunter regions. It has also been found on the North Coast from Ballina to the Port Macquarie Hastings region, and in the South East in the Illawarra and Shoalhaven districts.

It is native to South America. It was introduced to Australia as an aquatic ornamental plant and was first recorded as naturalised near Sydney in 1991.

What type of environment does it grow in?

Long-leaf willow primrose grows in sandy, silty soil in water bodies, including wetlands and riparian areas, swamps, marshes, drains and channels.

Maps and records

• Recorded presence of Long-leaf willow primrose 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 seed

Most spread is by seeds. Mature plants can produce up to 2.45 million seeds per plant. Seeds are spread in moving water, wind and by birds. They can also spread by contaminated soil or mud stuck to machinery, vehicles, footwear or clothing.

By plant parts

Long-leaf willow primrose is occasionally spread by broken stem fragments that are moved in flood waters.

References

Chandrasena, N. (2005). Ludwigia peruviana (L.) Hara and Ludwigia longifolia (DC.) Hara in Sydney: from immigrants to invaders. In Proceedings of the 20th Asia-Pacific Weed Science Society Conference.(Eds M. Mortimer, K. Itoh, T. Phuc Tuong, L. Cam Loan & N. Hong Son). Ho-Chi-Minh City, Vietnam (pp. 121-130).

Identic Pty Ltd. and Lucid central (2016). Environmental Weeds of Australia Fact sheet: Ludwigia longifolia (DC.) H. Hara. Retrieved August 2021 from https://keyserver.lucidcentral.org/weeds/data/media/Html/ludwigia_longifolia.htm

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 24 August 2021 from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ludwigia~longifolia

Sainty, G. R., & Jacobs, S. W. (2003). Waterplants in Australia (No. Ed. 4). Sainty and Associates Pty Ltd.

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.

To manage long-leaf willow primrose:

• contact your local council weeds officer to seek advice on identification and control methods
• use physical removal for small, isolated infestations before they set seeds
• if plants are seeding collect and bag seed heads and dispose of appropriately
• plant native riparian species to compete with and reduce regrowth
• limit access to the site from the public, animals and machinery.

Prevention

Plant riparian vegetation that can outcompete long-leaf willow primrose. Reducing nutrient runoff into the waterway can limit growth. To stop the spread of seeds prevent public and machinery access to sites with long-leaf water primrose. If possible limit animal access to the sites as well.

Physical removal

Seedlings can be pulled or dug out. Avoid breaking the plant and leaving behind pieces that could start new infestations. It is best to remove plants before they set seed to avoid spreading the seeds.

Disposal

Plants can be destroyed by burning or deep burial. Contact your local council for further advice on how to dispose of this weed.

Chemical control

Spot spraying

When: Apply herbicides from 1 September till 30 June or before flowering.

Apply to all foliage to the point of visible wetness.

Once plants have been killed by herbicides, follow up burning can be useful.

Herbicide options

See Using herbicides for more information.

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PERMIT 14731 Expires 30/06/2024
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 1.0 L per 100 L of water
Comments: Spot spray application. Apply from 1st September to 30th June, or before flowering occurs. See permit for more critical use comments.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
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.
Hunter	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
North Coast Exclusion (eradication) zone: Bellingen Shire LGA, Clarence Valley LGA, Lord Howe Island. Core infestation (containment) zone: Ballina Shire LGA, Byron Shire LGA, Coffs Harbour City LGA, Kempsey Shire LGA, Kyogle Shire LGA, Lismore City LGA, Nambucca Valley LGA, Port Macquarie-Hastings LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
South East	Regional Recommended Measure* (for Regional Priority - Eradication) 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