Photo guide to weeds

Parthenium weed (Parthenium hysterophorus)

  • Photo of the Parthenium weed
    Parthenium weed
  • Photo of the Parthenium Weed
    Parthenium weed infestation

General information

Parthenium found in Australia is native to North America but a distinctly different biotype occurs in South America. Parthenium is an annual herb with a deep taproot and an erect stem that becomes woody with age.

Parthenium costs the beef industry a total of $16.5 million per year and cropping industries several million dollars per year.

Parthenium weed is a declared Class 2 pest plant under Queensland legislation and a Weed of National Significance (WONS).

Scientific name Parthenium hysterophorus
Similar species Annual ragweed
Description
  • Grows to 1 to 1.5m high, developing many branches in its top half when mature.
  • Pale green leaves, up to 2mm long, deeply lobed and covered with fine soft hairs.
  • Small creamy white flowers on stem tips. 4 to 10mm in a 5 sided shape.
  • Flowers contain four to five black seeds that are wedge-shaped, 2mm long with two thin, white scales.
Habitat
  • Grows in most soil types, most dominant in alkaline, clay and loam soils.
  • Found along roadsides, railway lines, pastures and disturbed areas.
Distribution
  • Parthenium found in Australia is native to North America but a distinctly different biotype occurs in South America.
  • Initially recorded at Toogoolawah in 1955 and north of Clermont in 1960.
  • Well-established in Central Queensland, west to Longreach and northern and southern Queensland.
  • Infestations also found in New South Wales.
Life cycle
  • Normally germinates in spring and early summer, produces flowers and seed throughout its life and dies around late autumn.
  • With suitable conditions (rain, available moisture, mild temperatures), can grow and produce flowers at any time of the year.
  • In summer, can flower and set seed within four weeks of germination, particularly if stressed.
Spread Seeds spread by water, vehicles, machinery, and stock, feral and native animals and in feed and seed.
Impacts

Environmental:

  • Invades disturbed bare areas along roadsides, heavily stocked areas around yards and watering points.

Economic:

  • Invades pastures.
  • Reduces beef production.
  • Costs cropping industries millions of dollars per year.
  • Competes with crops for nutrients and space.

Social:

  • Pollen contains potent allergens that can cause reactions such as dermatitis and hay fever.
  • Affects human health in several countries.
Prevention
  • 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
  • Pastures maintained in good condition, with high levels of grass crown cover, will limit parthenium colonisation.
  • Drought, and the subsequent reduced pasture cover, creates the ideal window of opportunity for parthenium colonisation when good conditions return.

Hand weeding small areas is not recommended because:

  • there is a health hazard from allergic reactions
  • danger that mature seeds will drop off and increase the area of infestation.
Herbicide control

Non-crop areas:

  • Spray early before it can set seed. Keep a close watch on treated areas for at least two years.
  • Treat small and/or isolated infestations immediately. Herbicide control will involve a knockdown herbicide to kill plants that are present and a residual herbicide to control future germinations. Repeated spraying may be required even within a single growing season to prevent further seed production.
  • Extensive infestations will require herbicide treatment in conjunction with pasture management. Timing of spraying is critical so that parthenium is removed when plants are small and before seeding has occurred. Grasses should be actively growing and seeding so that they can recolonise the infested area.
  • See the parthenium fact sheet (PDF, 351.1KB) for herbicide control and application rates.

Cropping areas:

  • Controlling parthenium in cropland requires selective herbicide use and/or crop rotations. For further information on parthenium control in crops consult your local agronomist or local government officer.
Biological control
  • The combined effects of biological control agents reduced the density and vigour of parthenium and increased grass production.
  • There are currently a number of insect species and two rust pathogens that have been introduced to control parthenium:
    • Epiblema strenuana (stem galling moth)
    • Listronotus setosipennis (stem weevil)
    • Zygogramma bicolorata (leaf beetle)
    • Smicronyx lutulentus (seed weevil)
    • Conotrachelus albocinereus (stem galling weevil)
    • Bucculatrix parthenica (leaf feeding moth)
    • Carmentia ithacae (root feeding moth)
    • Stobaera concinna (sap feeding plant hopper)
    • Platphalonidia mystica (stem boring moth)
    • Puccinia abrupta var. partheniicola (leaf rust)
    • Puccinia xanthii var. parthenii-hysterophorae
Declarations details
  • A declared Class 2 species under the Land Protection (Pest and Stock Route Management) Act 2002.
  • Taking for commercial use, introduction, keeping, releasing and supplying (including supplying things containing reproductive material of this pest) is prohibited without a permit issued by Biosecurity Queensland.
  • Landholders are required to control declared pests on their properties.

Last updated 26 February 2013