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Parthenium weed (Parthenium hysterophorus)

How does this weed affect us?

Parthenium weed invades pastures and crops. It causes severe human health problems including:

  • respiratory problems
  • severe dermatitis.
It can also cause health problems in livestock.

Parthenium weed:

  • is unpalatable to livestock
  • outcompetes pastures
  • can taint meat or milk
  • reduces crop yields
  • contaminates grain
  • is a host plant for crop viruses.

Where are you likely to find it?

Parthenium weed has recently been found in many locations across NSW.

Look for it where:

  • livestock (including poultry) have been fed grain or hay, particularly if it has come from Queensland
  • earthworks have taken place, particularly if machinery has been in Queensland
  • there is bare soil (cultivated areas, roadsides, poor pastures)
  • grain crops have been harvested by a contractor.
Check regularly and especially after rain.

What does it look like?

It usually grows up to 1.5 m tall but can be up to 2 m tall.

Leaves are pale green and covered in soft fine hairs. Lower leaves are 5–20 cm long and deeply divided. Upper leaves are smaller and less divided.

Flowers are creamy white, 4–6 mm across and star-like with 5 distinct corners. Flower clusters are delicate and look a bit like "baby 's breath".

Stems are grooved, woody when older, and have many branches when flowering.