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Water primrose (Ludwigia peruviana)

In Australia, Ludwigia can form tall, dense stands that outcompete other plants and reduce stream flow. It can also increase sedimentation and lower oxygen levels in the water, damaging aquatic habitats.

Key facts

Type: Weed, shrub.

Native to: Central and South America.

Established in: NSW.

Other names: Primrose willow, Peruvian primrose, Willow primrose.

Best time to act: Look for seedlings in spring and summer and treat actively growing plants at or beyond early bloom, before the autumn change of colour.

Identification

  • A shrub that can grow to 3 m high, with stems that are hairy, especially when young.
  • Its alternate, stalkless leaves are egg-shaped to lanceolate, 4–12 cm long and 3–15 mm wide.
  • Yellow flowers grow singly where the leaves meet the stems and have four, occasionally five, petals that are 1–3 cm long.
  • The erect, hairy fruit is a 1–2 cm capsule with rusty red sepals remaining attached at the top; it contains numerous light-brown seeds.
  • Look-alike: The native Ludwigia peploides ssp. montividensis has a long, narrow fruit, floating stems that root at the nodes, and a longer leaf stalk.
  • Look-alike: Long-leaved Water Primrose (Ludwigia longifolia) is similar but does not have hairs on its stems, leaves or fruit.

Where it grows

In New South Wales, it occurs mostly along the coast in the greater Sydney region and is also recorded from the Wollondilly area.

Why it matters

  • Dense stands can intercept almost all light and dominate other water plants, sometimes leading to the loss of native plants and animals.
  • Accumulated organic material can deoxygenate the water, contributing to aquatic fauna deaths and changes in plant species composition.
  • It reduces stream flow and increases sedimentation.
  • It can interfere with access to water for animals, swimming and boating, reduce water quality, and block pumps.

How it spreads

  • It spreads by seed and vegetatively from stem pieces; seedlings and stem fragments can establish on strand lines or form floating islands.
  • Floating islands can grow, take root in shallow water, or detach in floods and establish elsewhere.
  • Seeds can adhere to clothing, hair, feathers and machinery, and wet seeds may be carried by birds to other wetlands.

Control options

  • Focus management on seedlings and the soil seed bank to reduce the main source of spread; seedlings can be controlled during the first 18 months before seed set.
  • Use registered herbicides when plants are actively growing, at or beyond early bloom but before their autumn colour change, and ensure thorough coverage.
  • Slashing stands before flowering and treating regrowth 2–4 weeks later can improve spraying results; larger plants may need repeat applications.
  • Follow up to manage seedlings; shading can suppress germination, and the soil seed bank may be greatly reduced after two or three years without new input.

Hygiene and washdown

  • Check and clean clothing and machinery to avoid carrying seeds, which can adhere to them.
  • 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: Restricted matter, categories 2, 3, 4, 5. Report it to Biosecurity Queensland within 24 hours; do not give it away, sell or release it into the environment; do not move it; do not keep it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 4 of 11 regions. Regional priority weed in Central West, North Coast, North West, South East. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • 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: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • 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.

  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development

Sources