Quick Facts

Quick facts

  • Burr Ragweed (Ambrosia confertiflora), a native plant of North America, is an erect perennial herb to 2 m high, forming large colonies from creeping runner-like roots.
  • It inhabits the dry plains of New South Wales and Queensland, especially in run-down pastures, orchards, roadsides, wastelands and other disturbed areas.
  • Burr Ragweed can be spread long distances by movement of seed, which hooks into animals and clothing, and by water, especially floods. Creeping roots ensure the continued growth of existing colonies.
  • It causes problems in agriculture by competing with pasture plants, contaminating wool and interfering with the harvest in orchards.
  • Its pollen is highly allergenic.
  • It can be controlled successfully with herbicides.

What Does It Look Like?

What is it?

Burr Ragweed (Ambrosia confertiflora) is an erect perennial herb to 2 m high, forming large colonies from creeping runner-like roots. It has grey-green, twice-divided, fern-like leaves, 12–16 cm long and 10–15 cm wide.

Flowers are yellow-green and of two kinds. The male flower consists of shortly stalked hemispherical heads (made up of many tiny male florets), 1 cm in diameter, which are grouped into branching spikes at the ends of the stems. The female florets, without petals, form 1-flowered heads, 5 mm long and 4 mm wide, clustered between the base of the upper leaves and the stems, and surrounded by a ring of spiny bracts (modified leaves). In the male flowers, the bracts are not spiny and they are fused together.

The fruit is about 4 mm long and covered with 10–20 short, hooked spines (Parsons & Cuthbertson 2001). The seeds are brown, woody, 3–4 mm in diameter a

For further information and assistance with identification of Burr Ragweed, contact the herbarium in your state or territory.

Flower colour

Yellow, Green

Growth form (weed type/habit)


Where it currently grows? Preferred habitat

Burr Ragweed occurs in the dry plains of temperate regions, on a variety of soils especially in run-down pastures, orchards, roadsides, wastelands and other disturbed areas (Parsons & Cuthbertson 2001).

Are there similar species?

Burr Ragweed is reminiscent of Chrysanthemum, in the height and leaf form, but the flowers are inconspicuous. Several other weed species are similar, such as Perennial Ragweed (Ambrosia psilostachya) and Chinese Mugwort (Artemisia verlotiorum) (Southern Tablelands and South Coast Noxious Plants Committee undated) but Artemisia species have heads that contain clusters of flowers of both sexes. The seeds of Burr Ragweed have 10–20 short hooked spines, whereas the seeds of Perennial Ragweed have a short pointed beak surrounded by 4–5 blunt projections (Parson & Cuthbertson 2001).

Why Is It A Weed?

What are its impacts?

Agriculture: Burr Ragweed is an extremely competitive plant, readily suppressing pasture species, including Rhodes Grass (Chloris gayana). Its burrs contaminate wool and because of the hooked spines, are not easily removed during scouring. This adds to the cost of processing, because acid carbonate must be used for removal. The plant is also a problem in orchards, competing for nutrients, interfering with the harvest, and both pollen and burrs cause discomfort to pickers.

Human impact: As with the other Ambrosia species, Burr Ragweed is noted for the amount of allergenic pollen it produces, causing severe hayfever and contact dermatitis in susceptible people (Parsons & Cuthbertson 2001).

How does it spread?

Burr Ragweed can be spread long distances by movement of seed, which becomes attached with hooked spines to sheep and other animals, clothing and other fibrous material. It is also spread by water, especially during flooding, as the woody burr is buoyant. It is commonly spread in soil and gravel used in road building and in soil used for top dressing. Natural growth of existing colonies occurs because of the creeping roots and transfer of root fragments severed during cultivation capable of becoming whole plants and colonising new areas (Parsons & Cuthbertson 2001).

What is its history in Australia?

It is not known how, when or why Burr Ragweed arrived in Australia, but it was first recorded at Cloyna, in Queensland, in 1950 (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Chemical control: Herbicides give good control in pastures, suppressing the Burr Ragweed and allowing pasture species to compete effectively. Spraying is usually performed at the budding stage of growth (Parsons & Cuthbertson 2001).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.

Non-chemical control: Physical control: Burr Ragweed is not effectively controlled by cultivation. In fact, it usually makes the infestation worse by spreading pieces of the perennial root and stimulating development from root buds.

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

The seeds of Burr Ragweed germinate in autumn and the rootstock and runners are established during winter. Growth increases in spring and flower stems are produced in early summer. Flowering begins in mid-summer and continues until early autumn. Aerial growth dies in autumn and new growth develops from the rootstock and creeping roots (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

In Queensland, Burr Ragweed is confined to small colonies in the western Darling Downs and the Burnett Pastoral District.

In New South Wales, colonies occur on the Far Western and North Western Plains and on the Central Western Slopes (Parsons & Cuthbertson 2001).

Where does it originate?

Burr Ragweed is a native of the semi-arid plains of the southern United States and Mexico (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Ambrosia confertiflora

Other scientific names (synonyms)?

  • Franseria confertiflora (DC.) Rydb.
  • Franseria tenuifolia Harv. & Gray

Does it have other known common name(s)?

Slimleaf Bursage

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