Fennel

(Foeniculum vulgare)
Fennel, photo: Tim Rudman

What is fennel?
  • Fennel is a significant weed of open, exposed sites like roadsides, railways, wastelands, channels and drains which receive abundant water or runoff. Fennel is also grown as a commercial crop in Tasmania.
  • Fennel is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of fennel are prohibited in Tasmania.

How to identify fennel

  • Fennel is a perennial (long-lived) herb with a stout branched taproot, jointed stems and feathery leaves that smell like aniseed. Fennel typically grows to between 1.5 to 2 metres high.
  • Flowering stems are produced from the centre of the plant each spring bearing an umbrella of small greenish yellow flowers. Aromatic seeds replace the small flowers at the ends of the flowering stems in summer and autumn.
  • For further help in identifying fennel, search the Dennis Morris Weeds and Endemic Flora database for fennel illustrations. If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.

Fennel in Tasmania

  • Fennel is a common roadside weed in Tasmania, and is also found along creek lines and streams and in waste areas receiving moderate rainfall or run-off. Significant infestations of fennel occur at Orielton Lagoon, around Glenorchy, and at Devonport.
  • Once well established fennel excludes most other plants, possibly due to the plant's unusual chemical properties.
  • Whilst fennel is a weed, the plant also has many useful attributes and has long been used as a vegetable and for its medicinal qualities. Trash resulting from harvesting of commercial crops is also used as garden mulch.

What is the legal status of fennel in your area?

Detailed management and control guidelines for fennel can be found in the Fennel Control Guide. Refer also to Herbicides for Fennel Control. For further information see Weed Links and Resources.

See also
Herbicides for Fennel Control
Statutory Management Plan for Fennel
Weed Links and Resources

Other useful links
Pest Genie
APVMA

Fennel Control Guide

Do

  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see Herbicides for Fennel Control for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Revisit and regularly inspect the site and ensure follow-up is undertaken;
  • Use a combination of different control methods; and
  • Establish vigorous pasture (or native species) after removal to reduce re-infestation.

Don't

  • Don't introduce fennel to fennel-free areas (e.g. by failing to wash down machinery and equipment between sites);
  • Don't start your control program without first planning your approach;
  • Don't allow fennel to flower and set seed before treatment;
  • Don't rely on one attempt at removal - follow-up is essential;
  • Don't rely on just one control method.

Spread of fennel

  • Fennel is spread mainly by seed. Fennel seed falls to the ground very near the parent plant.
  • Longer-distance movement of seed occurs where seeds contaminate agricultural produce, machinery, animal skins and human clothing. Seeds are also spread in water along drainage lines.
  • Fennel can regrow from crown and root fragments. Spread occurs when crown or root fragments are moved by cultivation or earth-moving machinery.

Avoid the introduction of fennel

  • Avoid introducing fennel seed or root fragments into clean areas, or into areas from which the weed is being eradicated.
  • Implements and vehicles which have been used on infested areas should be thoroughly cleaned before leaving the site.
  • See the Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading fennel.

Physical removal

  • Fennel can be grubbed out, but all root material needs to be removed to stop re-sprouting from root fragments.
  • Slashing can be used before and over the flowering period to reduce fennel seeding.

Chemical control

Herbicides for Fennel Control

Herbicides for Fennel Control

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To the extent permitted by law, the Department of Natural Resources and Environment Tasmania (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using information or material (in part or in whole) contained on this website.​