Crofton weed (Ageratina adenophora)

Crofton weed is a rapid-spreading shrub. It is a nuisance in many areas along the eastern coast of Australia.

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How does this weed affect you?

Crofton weed spreads quickly and: 

• is poisonous to horses 
• reduces crop yields 
• competes with pasture grasses, reducing productivity 
• outcompetes native plants 
• reduces habitat and food for native animals. 

Livestock poisoning 

Crofton weed can cause death in horses. Grazing crofton weed for as little as eight weeks can cause sickness.  Horses may graze crofton weed even when there is plenty of other feed. Inhaling the pollen could also make horses sick.  

The first sign of crofton weed poisoning is coughing which can become much worse by exercise. Continuing to graze the weed will damage the horse’s lungs and heart. Horses will then be short of breath, even when at rest. Eventually they may die from respiratory failure. Affected horses often suddenly collapse and die during work. 

It is not possible to treat Crofton weed poisoning. Early detection and removing horses from the weed is the best approach. If you suspect poisoning, seek veterinary advice.  

What does it look like?

Crofton weed is an erect, perennial multi-stemmed shrub 1–2 m tall.

Leaves are:

• dark green
• 4–12 cm long, 3–9 cm wide
• triangular to diamond shaped with a pointed tip and broad base
• toothed along the edges
• slightly crinkled and with prominent hairy veins
• on stalks 2 - 4 cm long.

Flowers are:

• white
• 5-8 mm in diameter
• daisy-like but without petals
• in clusters on the end of stems
• present in spring.

Seeds are:

• black
• 1-2 mm long
• tipped with white hairs 3-4 mm long.

Stems are:

• reddish to purplish brown when young and grey when old
• soft when young and woody as they age
• smooth and cylindrical
• branched.

Roots include:

• a pale yellow thick root that smells like carrot
• many branching roots that can spread 1 m from the base of the plant and up to 40 cm deep

Similar looking plants

Crofton weed looks like mistflower (Ageratina riparia), which has narrow spear- shaped leaves. It is usually shorter (up to 30 cm) and the stems are often spreading rather than upright.

Where is it found?

Crofton weed grows on the NSW east coast as far south as Wollongong, becoming more common further north. There are isolated infestations on the Northern and Central Tablelands.

The plant was introduced as a garden plant and naturalised around 1900. During the 1940s and 1950s, it spread rapidly. In some areas, dairy farmers and banana growers abandoned their farms due to the crofton weed infestations. It has been growing in the Sydney region since the early 1970s.

Crofton weed is native to Mexico. It is a weed in India, Sri Lanka, the Canary Islands, Jamaica, mainland United States, Hawaii, Fiji, and New Zealand.

What type of environment does it grow in?

Crofton weed prefers coastal areas with well-drained soil and a high annual rainfall (more than 1500 mm /year). It is not very frost tolerant. It can grow in steep areas. Most infestations are on bare or disturbed sites. Infestations in well vegetated areas are rare. Seedlings can tolerate shade and grow rapidly once established. It is commonly found in:

• cleared land
• roadsides and waste areas
• ungrazed small holdings
• woodlands and forests
• abandoned banana plantations
• fence lines and easements.

Maps and records

• Recorded presence of Crofton weed during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  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?

Mature plants can produce between 10,000 and 100,000 seeds per year. The seeds require light to germinate therefore infestations are much more likely on bare disturbed sites than heavily vegetated areas.

Seeds are spread:

• by wind and water
• in contaminated agricultural produce
• in contaminated soil
• by mud stuck to vehicles and machinery, animals, people’s boots or clothing.

References

Harvey, K.J., McConnachie, A.J. Sullivan, P. Holtkamp, R. & Officer, D. (2021). Biological control of weeds: a practitioner's guide for south east Australia. New South Wales Department of Primary Industries, Orange. 

McKenzie, R. (2020). Australia's poisonous plants, fungi and cyanobacteria: A guide to species of medical and veterinary importance. CSIRO PUBLISHING. 

Parsons, W.T. & Cuthbertson, E. G. (2001). Noxious weeds of Australia. CSIRO publishing. 

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 6 June from:  https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Ageratina~adenophora

Trounce B. & Dyason R. (2003). Crofton weed. Agfact P7.6.36. NSW Agriculture, Orange.  

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means looking for and killing regrowth or new seedlings. Using a combination of control methods is usually more successful.

Pasture management

Dense pastures suppress seed germination. Combine pasture improvement, slashing and herbicide treatments to restore infested land.

Grazing

Livestock eat young seedlings while grazing other plants. Goats will eat mature Crofton weed and may be useful to help control widespread infestations. Some knowledge of goat husbandry and fencing is essential. How well goats can control the weed depends on stocking rate, weed density, and the availability of other suitable feed. Only use the same goats for one or two seasons or they may develop chronic health problems.

Physical removal

By hand

Pull or dig out small areas of scattered plants. Remove crowns to prevent regrowth.

Slashing

Slashing can control heavy infestations on accessible land. Regular slashing will reduce flowering, seedset, vigour and density of the infestations. Slashing combined with maintaining competitive pastures will help control crofton weed. Horses will still eat slashed and dried Crofton weed. Keep horses away until the plant is completely removed from the paddock.

Avoid slashing flowering or seeding plants as the seeds can be spread by the slasher.

Biological control

Three biological control agents have established in Australia for crofton weed:

• Crofton weed rust fungus (Baeodromus eupatorii), which attacks the young leaves. This agent is suitable for redistribution.
• Crofton weed leaf spot fungus (Passalora ageratinae), which also attacks the leaves, is already widespread and does not need redistribution.
• The gall fly (Procecidocares utilis) causes swelling and death in the stems of the plant. This agent is also already widespread and does not need redistribution.

The combined effect of these agents can have a significant effect on crofton weed.

The accidentally introduced fungus (Cercospora eupatorii) and a native crown-boring insect (Dihammus argentatus) also attack Crofton weed.

Chemical control

Spray actively growing plants before they start flowering. Check labels for specific timing.

A combination of slashing and chemical application can be used to eradicate Crofton weed. Spraying can be in combination with slashing. After slashing, wait till plants are 15 - 40 cm tall and then spray.

Herbicide options

See Using herbicides for more information.

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2,4-D 300 g/L + Picloram 75 g/L (Tordon® 75-D)
Rate: 650 mL per 100 L of water
Comments: For use in grass pasture when weed is actively growing.
Withholding period: Do not graze or cut crops (except sugar cane 8 weeks) or pastures for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Fluroxypyr 140 g/L + Aminopyralid 10 g/L (Various products)
Rate: 700 mL in 100 L of water
Comments: Spot spray application. Apply to actively growing plants from October to April
Withholding period: Not required for pastures when used as directed. Do not graze or cut crops for stock food for 7 days after application. See label for export restrictions.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Fluroxypyr 200 g/L (Various products)
Rate: 500 mL per 100 L of water
Comments: Apply to actively growing seedlings and young plants up to flowering.
Withholding period: Do not graze failed crops and treated pastures or cut for stock feed for 7 days after application. See label for further information.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 300 mL in 100 L of water
Comments: Spray actively growing seedlings and young plants up to flowering.
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 500 mL per 100 L of water
Comments: Actively growing plants with full foliage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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MCPA 340 g/L + Dicamba 80 g/L (Kamba® M)
Rate: 190–270 mL per 100 L of water
Comments: Spray during active growth. For use in grass pastures.
Withholding period: Do not 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

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MCPA 340 g/L + Dicamba 80 g/L (Kamba® M)
Rate: 2.8–4.0 L/ha
Comments: Spray during active growth. For use in grass pastures.
Withholding period: Do not 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

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Metsulfuron-methyl 300 g/kg + Aminopyralid 375 g/kg (Various products)
Rate: 30 g per 100 L of water (always add a Wetter 100 mL/100L)
Comments: Spray to thoroughly wet all foliage but not to cause run-off. Best results obtained on younger plants. If regrowth occurs, retreat in the subsequent growth period. Adjuvant: Wetter 1000g/L non-ionic alcohol alkoxylate (Titan wetter 1000 or BS1000 or equivalent)
Withholding period: Pastures - Grazing for meat production or cutting for animal feed: Do not graze for 56 days after application. See label for further details
Herbicide group: 2 (previously group B), Inhibition of acetolactate and/or acetohydroxyacid synthase (ALS, AHAS inhibitors) + 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: High/Moderate

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Metsulfuron-methyl 600 g/kg (Various products)
Rate: 15 g per 100 L of water
Comments: Add surfactant. Thoroughly wet all foliage to point of run-off up to bud stage to prevent seed set.
Withholding period: Nil (recommended not to graze for 7 days before treatment and for 7 days after treatment to allow adequate chemical uptake in target weeds).
Herbicide group: 2 (previously group B), Inhibition of acetolactate and/or acetohydroxyacid synthase (ALS, AHAS inhibitors)
Resistance risk: High

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Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 350 mL in 100 L of water
Comments: Spray all foliage of actively growing plants to point of run-off (spring to autumn).
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

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Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 350 mL per 100 L of water
Comments: Spring to autumn. Spray all foliage to point of run-off. Actively growing plants.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 500 mL per 10 L of water
Comments: Gas gun / Splatter gun application. Apply to actively growing bushes.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the 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.
Hunter	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2024