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Fennel (Foeniculum vulgare)

Fennel is an introduced weed found across much of Australia, especially in disturbed areas and along roads, railways and waterways. It can form dense stands that compete with other vegetation and smother native plants.

Key facts

Type: Weed, herb.

Native to: Southern Europe, northern Africa and western Asia.

Established in: QLD, NSW, ACT, VIC, TAS, SA, WA.

Other names: Anise, Aniseed, Wild Fennel, Sweet Anise.

Best time to act: Look for and treat plants while they are young and before flowering, which generally begins around November and continues until autumn.

Identification

  • An erect herb, usually 1–2 metres tall but sometimes reaching 2.5 metres, with a stout, branched taproot.
  • Plants are usually smooth and have a strong aniseed scent; the robust stems have lengthwise ridges.
  • The alternate leaves are feathery, with many fine, thread-like segments, and can be 30–50 centimetres long.
  • Small yellow flowers grow in umbrella-shaped clusters at the ends of branches.
  • Look-alike: Wild carrot (*Daucus carota*) has similar umbrella-shaped flower heads, but its flowers are white or pinkish and its crushed leaves smell carroty rather than of aniseed.
  • Look-alike: Hemlock (*Conium maculatum*) has white flowers and a strong smell that is not aniseed; aniseed plant (*Pimpinella anisum*) has a similar aroma.

Where it grows

In Australia, fennel occurs in the ACT, NSW, Queensland, South Australia, Tasmania, Victoria and Western Australia, in places including roadsides, railways, waterways, disturbed areas, grasslands and open woodland.

Why it matters

  • Established plants compete with other vegetation and can form dense stands that exclude other plants.
  • Along roads, railways and waterways, fennel can prevent native plants from establishing or shade out existing plants.
  • It occurs in agricultural areas, particularly degraded pastures, and in urban gardens and other disturbed sites.
  • Dense infestations along waterways may restrict some recreational activities.

How it spreads

  • Fennel spreads mainly by seed, which can disperse more than 200 metres from the parent plant.
  • Water can carry seed along waterways and drains; seed may also be moved in contaminated soil, gravel, vehicles, machinery, stock and clothing.
  • Pieces of root or crown moved during cultivation can resprout and establish elsewhere.

Control options

  • Treat plants while young, before they elongate and flower, when they are easier to remove or more susceptible to registered herbicides.
  • Spot spray actively growing young plants using registered herbicides; cut-and-paint treatment can be used in winter to spring before new growth, with cuts made close to the base.
  • Hand-chip young plants and follow up to control seedlings; take care when digging mature plants because pieces of root left behind can regrow.
  • Slashing just before flowering may kill plants, while repeat slashing of regrowth may be needed; follow approved methods and dispose of roots and foliage in hot compost.

Hygiene and washdown

  • Clean soil and seed from vehicles and machinery before moving between sites, as fennel seed and pieces of root or crown can be transported this way.
  • Avoid moving contaminated soil or gravel, and check clothing and gear for seed.
  • 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: Regionally controlled / restricted weed (varies by region). Where it is regionally controlled, landowners must take all reasonable steps to prevent its growth and spread on their land. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • 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.

  • 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
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources