Weed of the Month: Parthenium

If there is one weed we hope to never find in the Hastings region, it’s this one!

Parthenium weed isn’t big and spiky, but it sure packs a punch to human health, animals and other plants. Parthenium weed is a 1-1.5m tall herbaceous plant from the American tropics that is now a major weed in parts of Australia and India. It releases chemicals into the soil that inhibit the growth of other plants, and produces large amounts of pollen that can cause severe allergic reactions in people and animals. These reactions cause respiratory problems and dermatitis, and can get worse after multiple exposures to the weed. Livestock that eat Parthenium weed may suffer kidney damage and dermatitis.

Parthenium regrowth
Quick growing weed

Parthenium weed starts as a rosette, with lower leaves growing up to 20cm long and becoming deeply lobed. The pale green leaves are covered with soft hairs. They grow from ribbed stems, which have a striped appearance. The tiny flowers are 5mm across and clustered at the ends of stems. They are creamy white and star-shaped with 5 distinct points, without obvious petals. 

Seeds spread via machinery and crop

Each plant produces up to 15,000 long-lived seeds, with seeds produced in as little as 4 weeks in ideal conditions.  Young Parthenium weed can look very similar to other annual weeds such as ragweed (Ambrosia).  Parthenium weed spreads from infested areas (mainly in Central Queensland) by sticking to machinery and vehicles or as a contaminant in hay and grain. Some infestations in NSW have occurred due to seeds contaminating organic chicken feed. 

Report this weed to the biosecurity officer

You should always ensure that any machinery that enters your property, or animal feed that you purchase, is free from contaminants.   Any suspected infestations must be reported to the Biosecurity Officer – do not try to control this plant yourself.

Learn more about Parthenium weed by visiting NSW WeedWise or contacting the Biosecurity Officer directly.

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