Burr ragweed (Ambrosia confertiflora)

Burr ragweed is an erect perennial herb with spiny burrs. It competes with pasture plants, reduces productivity and the burrs contaminate wool.

Profile

How does this weed affect you?

Burr ragweed forms dense stands. It:

• outcompetes other plants
• is not palatable to livestock and can reduce productivity
• has burrs with hooked hairs which damage wool
• produces large amounts of pollen which can cause hay fever
• can irritate skin after contact with the plant.

What does it look like?

Burr ragweed is a perennial plant that can grow up to 2 m tall. Plants die back to the roots over winter then regrow quickly in spring and summer. They flower mid-summer to early autumn. During very dry summers plants can die back and re-sprout in autumn.

Leaves are:

• green to grey-green
• deeply lobed giving a fern-like appearance
• up to 16 cm long and 15 cm wide
• finely hairy on both surfaces
• fragrant
• on short stalks with wings where stalks join the stem
• opposite on the lower stems becoming alternate higher up the stem

 Flowers:

There are separate male and female flowerheads present in summer.

Male flowerheads are:

• yellow-green
• cup-shaped and droop downwards
• 1 cm in diameter
• on spike-like clusters. 

Female flowerheads are:

• below the male flowers
• 5 mm long and 4 mm wide
• singular and upright and grow In the leaf fork of the upper leaves

Fruit are:

• woody, brown burrs, covered in hooked spines
• around 4 mm long with a single seed
• in clusters.

Seeds are:

• brown and woody
• 3-4 mm in diameter
• egg-shaped or round
• covered in 10 - 20 short, stout, hooked spines.

Stems are:

• upright
• grey-green, green or whitish
• hairy
• up to 2m long.

Roots are:

• short and thick 
• dense
• usually growing in the top 30 cm but can reach 1 m deep.

Similar looking plants

Burr ragweed is similar to other ragweed species including:

• perennial ragweed (Ambrosia psilostachya) which has pointed triangular lobes on its leaves.
• annual ragweed (A. artemisiifolia), which can grow to 3.5 m and has no burrs on the seeds.
• lacy ragweed (A. tenuifolia) which is much shorter, only up to 75 cm and has grey hairy leaves with a lacy appearance.

It also looks similar to parthenium weed (Parthenium hysterophorus), which has white star shaped flowerheads at the end of stems rather than greenish yellow flowers.

Where is it found?

In NSW, burr ragweed is mostly found in the Western region. Isolated infestations have also been found in the North West, Central West and Riverina regions. It is also present in south-east Queensland.

Burr ragweed was introduced from the southern USA and Mexico.

Maps and records

• Recorded presence of Burr ragweed during property inspections (Map: Biosecurity Information System - Weeds, 2017-2026)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

The burred seeds can be spread by:

• sticking to clothing, wool and fur 
• water, including during floods
• people dumping green waste
• moving contaminated soil.

Seeds germinate in autumn. 

By plant parts

A new plant can grow from a root, or root fragment. These can be spread by people dumping green waste and in contaminated soil.

References

Auld B.A.  and Medd R.W. (1999). Weeds. An illustrated botanical guide to the weeds of Australia. Inkata Press, Melbourne.

Pasiecznik, N. (2020). CABI data sheet: Ambrosia confertiflora (burr ragweed). CABI Compendium. Retrieved 11 July 2025 from: https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.120550

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 2018 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ambrosia~confertiflora

More information

back to top

Control

Controlling burr ragweed can be difficult  because of its strong root system. Plants can sucker or re-sprout therefore cutting or mowing is not a good option and may make things worse. 

Prevention

Avoid moving soil, vehicles and machinery contaminated with burr ragweed roots or burrs. Clean vehicles or machinery before moving to a new site,

If possible do not graze livestock in areas with burr ragweed as they can spread the seeds to clean areas. 

Early detection

Learn to identify burr ragweed and remove plants early to reduce the chance of spread. Controlling small seedlings is easier and they won’t have dropped seed.

Physical removal

Hand pulling or digging out small plants may be effective if all the roots can be removed. If roots break off and stay in the soil the plant can regrow.

Chemical control

Spray actively growing plants. Ensure all of the foliage is covered.

Herbicide options

See Using herbicides for more information.

---

PERMIT 14249 Expires 31/03/2030
Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon® Extra)
Rate: 250-500 mL per 100 L
Comments: Spray plants less than 1.5 metres tall from October to May. For areas of native vegetation and non-cropland areas. See permit for critical comments.
Withholding period: Where product is used to control woody weeds in pastures there is a restriction of 12 weeks for use of treated pastures for making hay and silage; using hay or other plant material for compost, mulch or mushroom substrate; or using animal waste from animals grazing on treated pastures for compost, mulching, or spreading on pasture/crops.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

PERMIT 14249 Expires 31/03/2030
Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 250-500 mL per 100 L
Comments: Spray plants less than 1.5 metres tall from October to May. For areas of native vegetation and non-cropland areas. See permit for critical comments.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

Dicamba 750 g/L (Kamba® 750)
Rate: 5.9 L / ha Use a minimum of 1500 L/ha water carrier. Add a surfactant.
Comments: Boom spray for non-crop situations. Spray prior to flowering.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

Dicamba 750 g/L (Kamba® 750)
Rate: 400 mL /100 L of water
Comments: Spray prior to flowering. For non crop situations.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

Dicamba 750 g/L (Kamba® 750)
Rate: 87 mL / 15 L of water. Add a surfactant.
Comments: Spot spray prior to flowering. For non-crop situations.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

Glyphosate 360 g/L (Various products)
Rate: 10 mL /1 L water
Comments: Spot spray. For general weed control in Domestic areas (Home gardens), Commercial, Industrial and Public Service areas, Agricultural buildings and other farm situations.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

back to top

Biosecurity duty

The content provided here is for information purposes only and is taken from the NSW Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
Central Tablelands	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Central West	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Western	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

back to top

Reviewed 2025