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 is a rapid-spreading weed that has become a nuisance in many areas along the eastern coast of Australia. It is particularly invasive on cleared land that is not grazed, such as public reserves, and causes particular problems for horse owners.

Once established, seedlings tolerate shade and grow rapidly. In this way, small infestations of Crofton weed rapidly increase in size unless controlled.

Crofton weed reduces the ecological value of bush land, lowers crop yields and reduces the carrying capacity of grazing land.

The weed spread rapidly during the 1940s and 1950s and it was reported that in some areas dairy farmers and banana growers abandoned their holdings!

The area of Crofton weed infestation has now been substantially reduced through control strategies.

It is poisonous to horses

Horses may preferentially graze the plant even when ample feed is available. Access to Crofton weed for as little as eight weeks can cause sickness.

The first sign of Crofton weed poisoning is coughing, made more pronounced by exercise. If horses are not removed from infested areas, further lung and possible heart damage occurs, leading to shortness of breath even when at rest. Death from respiratory failure is the eventual result, with affected horses often suddenly collapsing and dying during work.

Treatment of Crofton weed poisoning is unlikely to reverse the damage, so early detection of poisoning and removal from the weed infestation is essential. If you suspect poisoning, seek veterinary advice. Poisoned horses may never again be capable of work.

It is possible that Crofton weed is at its most poisonous during or soon after flowering. Pollen inhalation could be a factor in poisoning.

It is a weed of non-agricultural areas

Crofton weed is an aggressive invader of public amenity land such as State forests, national parks and nature reserves, as well as public utility easements such as railway embankments.

What does it look like?

Crofton weed is a member of the Asteraceae or daisy family. It is an erect, perennial shrub with numerous chocolate-brown woody stems emanating from an underground crown and reaching a height of 1–2 m. It has broad, slightly crinkled, trowel-shaped, toothed leaves with chocolate-coloured petioles (leaf stems). It produces white flowers in spring. Crofton weed and mistflower are sometimes mistaken for each other. Table 1 distinguishes between the two species.

Table 1. Comparison between Crofton weed and mistflower.

	Crofton weed	Mistflower
Botanical name	Ageratina adenophora	Ageratina riparia
Growth habit	Erect stems up to 2m tall	Sprawling stems, prostrate to 30cm tall
Leaf shape	Trowel-shaped, broad-toothed	Narrow, elongated, toothed
Flowers	The plants have similar flowers

Where is it found?

Crofton weed is a native of Mexico. It is present as a weed in India, Sri Lanka, the Canary Islands, Jamaica, mainland United States, Hawaii, Fiji, New Zealand and Australia. Since its escape from ornamental cultivation in Australia around 1900, it has become widespread in Queensland coastal areas and on the New South Wales North Coast, and as far south as Wollongong. Isolated infestations also occur on the northern and central tablelands. The weed has been present in the Sydney region for more than 30 years and has spread rapidly in this area since the early 1970s. It is now a problem weed, especially on small farms where horses are kept.

Places where Crofton weed is commonly found include:

• land cleared but not revegetated with pasture
• roadsides and waste areas
• ungrazed small holdings
• State forests and National parks
• abandoned banana plantations
• fencelines.

Maps and records

• Recorded presence of Crofton weed during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  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 Crofton weed plants can produce between 10 000 and 100 000 seeds per year. Seeds are very light (25 000 seeds/g) and are windborne over long distances to invade previously non-infested areas. 

The seeds require light to stimulate germination so that invasion commonly takes place on bare, disturbed sites and only rarely on heavily vegetated areas.

What type of environment does it grow in?

Crofton weed and its close relative, mistflower (A. riparia), infest large areas of the coast, especially steep, well-drained land where annual rainfall is more than 1500 mm and where there are few or no frosts. The seeds require light to stimulate germination so that invasion commonly takes place on bare, disturbed sites and only rarely on heavily vegetated areas.

Places where Crofton weed is commonly found include:

• land cleared but not revegetated with pasture
• roadsides and waste areas
• ungrazed small holdings
• State forests
• National parks
• abandoned banana plantations
• fencelines.

Acknowledgements

Dr Chris Bourke, Senior Research Scientist, Orange Agricultural Institute.

References

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

More information

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Control

Crofton weed can be controlled using a combination of methods, in conjunction with pasture and grazing management practices, aimed at creating an unfavourable environment for weed invasion. 

Mechanical control

Small areas of scattered plants can be dug out with a mattock. Crowns should be removed to prevent regrowth. Slashing is often used to control heavy infestations on accessible land. Regular slashing will reduce flowering and seedset, thus reducing spread by seeds. It will also reduce the vigour and density of Crofton weed infestations and, combined with competitive pastures, will eventually bring them under control. The slashed and dried plant, however, is still attractive and toxic to horses. Take care to keep horses away until the plant has been completely removed from the paddock.

Grazing management

Well-managed, competitive pastures are important in preventing weed invasion and this principle also applies to Crofton weed. Dense pasture swards suppress seed germination and livestock eat young seedlings with the balance of their feed. Therefore, fewer plants grow to maturity. Goats are known to eat Crofton weed. The degree of weed control by goats depends on the stocking rate, weed density and the availability of other suitable feed. Using goats to help control widespread infestations may be worth considering, although some knowledge of goat husbandry and fencing is necessary. The same group of goats should be used for only one or two seasons to avoid risk of chronic health problems.

Biological control

The gall fly (Procecidocares utilis) was released in 1953 for the biological control of Crofton weed. It initially established readily and spread rapidly throughout the range of the weed. However, the insect itself was parasitised by a native insect and its effect is consequently patchy. Visible signs of insect infestation are galls or swellings about 1cm long in the stems of the plant. These galls contain the insect larvae. Galled stems usually die, but the level of galling is usually too low for any substantial effect.

A fungus that was accidentally introduced (Cercospora eupatorii) and a native crown-boring insect (Dihammus argentatus) also attack Crofton weed. The combined effect of these predators and the gall fly reduces the rate of spread of the weed. High levels of Crofton weed control have never been obtained through biological control agents, therefore they should never be solely relied upon.

Chemical control

Chemical treatment appears to work most effectively during late summer and autumn. When spraying Crofton weed with herbicides it is important to ensure that spray does not drift onto desirable plants and to maintain operator safety.

A combination of slashing and chemical application is often used to eradicate Crofton weed. After slashing, the weed is allowed to regrow from the crown to a height of 15–40 cm and then sprayed with herbicide. Combined with the introduction of competitive species, this strategy restores the productivity of infested land.

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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Fluroxypyr 140 g/L + Aminopyralid 10 g/L (Hot Shot™ )
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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Fluroxypyr 140 g/L + Aminopyralid 10 g/L (Hot Shot™ )
Rate: 1.5 L/ha
Comments: Boom 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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Fluroxypyr 200 g/L (Comet® 200 herbicide)
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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 300 mL in 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 food for 7 days after application. See label for more information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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: M, Inhibitors of EPSP synthase
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Metsulfuron-methyl 300 g/kg + Aminopyralid 375 g/kg (Stinger™)
Rate: 30 g per 100 L of water
Comments: Folia spray to thoroughly wet the plants.
Withholding period: 3 - 56 days (see label)
Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors) + I, Disruptors of plant cell growth (synthetic auxins)
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: B, Inhibitors of acetolactate synthase (ALS 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: Spring to autumn. Spray all foliage to point of run-off. Actively growing plants.
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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: I, Disruptors of plant cell growth (synthetic auxins)
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 2023