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Paddy's lucerne (Sida rhombifolia)

Paddy's Lucerne competes strongly for light and nutrients in crops and pastures, and can smother grasses in some east coast pastures. It is not readily grazed, has low nutrient value and can cause hairballs in stock that eat it.

Key facts

Type: Weed, shrub.

Native to: Tropical America.

Established in: QLD, NSW, NT.

Other names: Common Sida.

Best time to act: In northern Australia, seedlings emerge after the opening rains around September or October and flowering is mostly from December to April, so look for plants and treat them before flowering.

Identification

  • It is an upright, perennial sub-shrub that can grow to 1.5 m tall.
  • Young plants have a dense covering of minute hairs, which is mostly lost as they mature.
  • Leaves are 15–90 mm long, oval, egg-shaped or diamond-shaped, with shallow teeth on the upper two-thirds; the undersides are densely hairy and the upper surfaces sparsely hairy.
  • Yellow flowers about 15 mm across grow singly along the stems, becoming more crowded towards the tips.
  • The fruit is 4.5–5.5 mm across and splits into 9–11 segments, usually with two short awns on each segment.
  • Look-alike: Flannel Weed has broad or heart-shaped leaves with dense, felty hairs on both surfaces, clustered flowers on short stalks and longer awns on its fruit segments.
  • Look-alike: Spinyhead Sida has pointed, elongated leaves that are hairless or sparsely hairy, shorter flower stalks and fruit that splits into 5–8 segments.

Where it grows

In Australia it occurs in cultivated and disturbed sites, including roadsides and degraded pastures, and is widespread on the mainland, especially along the eastern coast and in the Northern Territory and northern Western Australia.

Why it matters

  • It competes for light and nutrients in crops and pastures and can smother grasses.
  • Its seed can contaminate harvested material.
  • It is not readily grazed and has low nutrient value; stock that eat it may develop hairballs from the plant's stringy bark.
  • In grasslands and woodlands it can compete with and exclude native species, particularly on degraded or overused land.

How it spreads

  • It reproduces and spreads only by seed, which can catch in fibrous material such as clothing and animal fur or hair.
  • Seed also spreads in streams and irrigation water, in hay and pasture seed, and in mud on footwear, hooves, machinery and vehicles.

Control options

  • Grub out small outbreaks before flowering, cutting the root well below the surface to reduce regrowth; repeated cultivation can control larger areas.
  • Slash plants before flowering to reduce seed production, and consider registered herbicides for seedlings, which are susceptible when up to 10 cm high.
  • Plants become resistant to most herbicides as they mature, so use approved methods suited to the plant's growth stage.
  • A dense, well-fertilised improved pasture can inhibit growth, but choose pasture species carefully because some, such as Buffel Grass, are serious environmental weeds.

Hygiene and washdown

  • Clean mud and plant material from footwear, machinery and vehicles, and avoid moving contaminated hay or pasture seed.
  • Yard stock for four to five days before moving them from infested paddocks to reduce seed carried in dung or on their hides.
  • 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: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. 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: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class B. Class B: growth and spread must be controlled. All declared weeds are also Class C, so they must not be brought into the NT.
  • 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.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources