Crofton weed

Native to Mexico and Central America, crofton weed is a shrubby perennial herb with red stems and bright green leaves. It was introduced to Australia in 1875 as an ornamental plant but then spread out of control. By the 1940s, newly cleared land along the Queensland - New South Wales border was overrun with the plant.

Crofton weed is now most prevalent in South East Queensland, invading pastures and colonising roadsides and forest edges. Crofton weed is also poisonous to horses, and causes Tallebudgera Horse Disease, which results in serious respiratory damage and death.

Crofton weed is not a prohibited or restricted invasive plant under the Biosecurity Act 2014.

Scientific name

Ageratina adenophora

Other names

  • Catweed, hemp agrimony

Description

  • Shrubby perennial herb with woody rootstock and upright branching stems, up to 1-2m tall.
  • Stems are red, growing duller with age, soft young stems can establish roots where they touch ground.
  • Leaves are bright green, opposite, trowel-shaped, 50-75mm long, 25-50mm wide, with toothed edges.
  • Flowers are white, 5-8mm wide, grow in small, dense heads at ends of branches.
  • Seeds are slender, angular, 2mm long, almost black, with fine white hairs at tip.

Habitat

  • Grows in wet shaded areas of fringing forest and along streams.
  • Favours south-facing damp slopes.
  • Found along roadsides and overgrazed pastures.

Distribution

  • Restricted to South East Queensland.
  • Scattered infestations occur in drier scrub soils

Life cycle

  • Usually buds in August and flowers from September.
  • Produces many windblown seeds.
  • Can germinate during wet summer periods and develop in 12 weeks to flower following spring.

Affected animals

  • Horses

Impacts

Economic

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

Social

  • In horses, causes serious respiratory damage leading to death.

How it is spread

  • Seeds spread by water and wind.
  • Also spread by machinery, vehicles, animals, footwear and clothing.

Control

Physical control

  • Chip-out small infestations before they flower.

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, 1MB) for herbicide control and application rates.

Biological control

  • A stem gall-fly (Procecidochares utilis) was introduced in 1952 but became heavily parasitised and now has little impact.
  • A leaf spot fungus (Phaeoramularia eupatorii-odorati) does have some effect, especially on seedlings.
  • White smut fungus (Entyloma ageratinae) has been released for mistflower and will have some impact on crofton weed.

Legal requirements

  • Crofton weed is not a prohibited or restricted invasive plant under the Biosecurity Act 2014. However, by law, everyone has a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with invasive plants and animals under their control.
  • Local governments must have a biosecurity plan that covers invasive plants and animals in their area. This plan may include actions to be taken on certain species. Some of these actions may be required under local laws. Contact your local government for more information.

Further information