Photo guide to weeds

Crofton weed (Ageratina adenophora)

  • Close up photograph of the flowers on a Crofton weed bush
    Crofton weed flowers
  • Close up photograph of the leaves on a Crofton weed plant
    Crofton weed

General information

Native to Mexico and Central America, crofton weed was introduced to Australia in 1875 as an ornamental plant but then spread out of control. Newly-cleared land along the New South Wales and Queensland borders was overrun in the 1940s.

Crofton weed is most prevalent in South East Queensland, invading pastures and colonising roadsides and forest edges. Crofton weed is an aggressive weed which is poisonous to horses, causing serious respiratory damage that can cause death.

Crofton weed in not a declared pest plant under Queensland legislation.


Scientific name Ageratina adenophora
  • Herb that is perennial, very shrubby with woody rootstock and upright branching stems. growing 1-2m high.
  • Stems red which dull with age, soft young stems establish roots where they touch the ground.
  • Leaves are bright-green, opposite trowel-shaped, 50-75mm long and 25-50mm broad, with toothed edges.
  • Flowers are white growing in small, dense heads at the ends of branches, 5-8mm across.
  • Seeds are slender, angular, 2mm seeds are almost black with fine white hairs at the tip.
  • Grows in wet shaded areas fringing forest and along streams
  • Favours southerly facing damp slopes.
  • Found along roadsides and overgrazed pastures.
  • Restricted to south-eastern Queensland,
  • Scattered infestations occur in drier scrub soils
Life cycle
  • Usually buds in August and flowers from September onwards.
  • Produces many windblown seeds.
  • Can germinate during wet summer periods and develop within 12 weeks to flower the following spring.
  • Seeds can spread by water and wind.
  • Can also spread by machinery, vehicles, animals, footwear and clothing.


  • Invades pastures.
  • On wet slopes invades kikuyu grass pasture.


  • In horses causes serious respiratory damage leading to death.

The best form of weed control is prevention. Treat weed infestations when they are small - do not allow weeds to establish.
Ways to prevent weed spread


Physical control

  • Chip out small infestations before flowering.

Mechanical control

  • Cultivation, grubbing, hoeing and burning, along with planting of competitive pastures combined with fertilisation, will control the weed in accessible areas.

Herbicide control

  • Herbicides are effective.

See the crofton weed fact sheet (PDF, 215KB) for herbicide control and application rates.

Biological control

  • A stem gall-fly (Procecidochares utilis) was introduced in 1952 but became heavily parasitised and now exerts little impact on plants.
  • A leaf spot fungus (Phaeoramularia eupatorii-odorati) does exert some effect, especially on seedlings.
  • White smut fungus (Entyloma ageratinae) is released for mistflower and will have some impact on Crofton weed.
Declaration details
  • not a declared species under Queensland legislation but may be declared under local government law

Last updated 26 February 2014