Parthenium Weed (Parthenium hysterophorus)

Parthenium Weed is a fast-growing plant from central and south America. It was first recorded in Australia in 1955 and has continued to spread across Queensland and patches of NSW. Parthenium Weed is a Priority Weed across NSW and has recently been found near Parkes, Walgett, Forbes, and Engadine. This weed can degrade pastures and crops along with causing various health issues in livestock and even humans.

Fortunately, most outbreaks in NSW have been controlled. However, it is important that we continue to prevent and slow the spread of this weed. 

What does Parthenium Weed look like?

Parthenium weed is an erect annual herb that usually grows around 1–1.5m tall but can grow to 2m tall.

Leaves are:

  • pale green.
  • lower leaves are 5–20 cm long and deeply divided.
  • upper leaves less divided and smaller.
  • covered with soft, fine hair.
  • alternate on the stem.
  • Most leaves die after the plant flowers.

Flowers are:

  • creamy-white and 4–6 mm in diameter.
  • star shaped with 5 distinct points.
  • made up of many tiny florets: each of the 5 points is a ray floret with petals and the centre has many (12-60) tiny tubular disc florets.
  • at the end of stems in clusters that look a bit like ‘baby’s breath’.

For a video on Parthenium identification please click here

Parthenium weed flowers:

Parthenium weed flowers.png


Parthenium weed seedling:

Parthenium weed seedling.png

How does it spread?

Parthenium weed primarily spreads by seed. The seeds can germinate, flower, and seed in the space of four weeks in good conditions. One plant can produce up to 15,000 seeds. The seeds can remain dormant in the soil for several years.

Spread is usually caused when machinery or vehicles pick up mud from infested areas and move through unaffected areas. It is also transported in contaminated soil, compost, mulch, feed, and even chicken feed. 

How is Parthenium a threat to NSW biosecurity?

Parthenium already covers a majority of western Queensland and is easily transported accidentally over the border. The plant can quickly cover entire areas and release a toxin into the soil stunting the growth of other plants, competing with crops and native species.

Parthenium is not palatable to stock and can cause poisoning and even death. It is also a health hazard to human health and can cause serious respiratory issues and contact dermatitis. 


Reporting Parthenium Weed sightings

If you have found a suspected outbreak of Parthenium Weed please do not attempt to treat or dispose of this weed yourself. Report the sighting by the Biosecurity Helpline on 1800 680 244. Alternatively, please contact Council's Biosecurity Team on 02 6861 2333.

NSW DPI and any relevant authorities will lead an initial response for the treatment and disposal of the plant to stop it from spreading.


Parthenium Weed control

Parthenium is listed as Prohibited Matter in NSW, and everyone is lawfully obliged to prevent the spread of this weed.

Landholders must always be mindful of importing or exporting machinery and organic matter and ensure that all relevant biosecurity measures are followed.

For more information, please see the links below: