What is onion weed?
- Onion weed is a pasture weed.
- Onion weed is a
declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of onion weed are prohibited in Tasmania.
How to identify onion weed
Image top: Onion weed plant in flower.
- Onion weed is an erect, clump-forming herb that grows to 75 cm high. The roots are fibrous, thick and yellow. The stems are rigid and hollow, while the leaves all emerge from the base of the plant and are almost cylindrical in cross section. The white or pink flowers are arranged alternately along the flowering stems which are longer than the leaves. The fruit is a globular, wrinkled capsule.
- Seeds germinate at all times but mainly in late summer and autumn. After flowering and fruiting in spring and summer the flowering stems die back but most leaves remain alive through summer. New leaves and stems are produced from the base of the plant in the autumn.
- For help in identifying onion weed, search the
Dennis Morris Weeds and Endemic Flora database for onion weed illustrations. If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.
Image above: Close-up of onion weed flower.
Onion weed in Tasmania
- Onion weed occurs as an occasional weed on King Island, Flinders Island and around Hobart.
- Onion weed can invade disturbed land such as roadsides, degraded pastures, neglected areas and sandy coastal environments. Onion weed infestations can reach high densities. The weed is unpalatable and can significantly reduce pasture carrying capacity.
What is the legal status of onion weed in your area?
Detailed management and control guidelines for onion weed can be found in the Onion Weed Control Guide. Refer also to
Herbicides for Onion Weed Control. For further information see Weed Links and Resources
Herbicides for Onion Weed Control
Statutory Management Plan for Onion Weed
Weed Links and Resources
Other useful links
Onion Weed Control Guide
- 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 the
Herbicides for Onion Weed Control link 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 introduce onion weed to onion weed-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 onion weed 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 onion weed
- Spread of onion weed is by seed.
- Onion weed seed can be spread by water, on wool and clothing, in produce, and on vehicles and farm machinery.
- Seed on dead plants can be spread during cultivation when the plant is dragged along by machinery, or when the dead plants are blown about by the wind.
- Seeds can remain viable in the soil for many years.
- 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 onion weed.
- Single plants and small infestations can be removed by hand-pulling or hoeing. Remove plants before seeding.
- Larger infestations should be controlled by cultivation or establishing a vigorous legume pasture.
- Onion weed is readily killed by cultivation as it does not have rhizomes or tubers from which plants can regrow.
- If plants are cut below the soil surface they will die. However, plants which are only partly turned over during cultivation can survive, particularly when the soil is moist.
- Cultivation may not be feasible on more arid sites where the weed occurs. A suitable program can be to cultivate in summer when the soil is dry to kill existing plants, cultivate in a second summer, and then plant a cereal crop under-sown with lucerne in early winter. Avoid grazing the lucerne in the first year.
- On non-arable land, sow with legume pasture to compete with germinating onion weed seedlings.
Herbicides for Onion Weed Control