Siam weed (Chromolaena odorata) is one of the Prohibited Matter weeds in NSW.
One of the world's worst tropical weeds
Although it has not been recorded here yet, it is considered a serious threat to people and agriculture. It is regarded as one of the world’s worst tropical weeds.
Siam weed is native to Central and South America, yet is becoming highly invasive across Africa, tropical America, India, China, South-East Asia and the Pacific. It was detected in Australia in 1994 and now infests areas around Townsville and far North Queensland, although it has been found in Rockhampton and north of Brisbane in recent years. Travellers to these regions need to be aware that weeds such as Siam can hitch a ride on vehicles and equipment, so they should be cleaned before returning home.
Fast growing scrambler
Siam weed grows extremely fast, climbing and scrambling over native vegetation to create dense thickets and reduced biodiversity. The plant emits a pungent odour when crushed, indicating its toxic properties. Siam weed has caused reactions and allergies in sensitive people and is highly toxic to livestock who graze on the plant or are given contaminated feed. It can dominate plantations of tropical crops such as bananas and sugarcane.
Siam weed presents a significant threat to agriculture in our region, and any suspected plants must be reported to council’s Biosecurity officer.
Identifying Siam weed
To those who know weeds, Siam has been described as looking like Billy goat weed or Crofton weed but with a size and growth habit similar to Lantana. It is an upright or sprawling shrub that develops woody stems as it matures. Siam weed leaves are usually arrow-shaped, 5-10cm long and 3-7cm wide. They can have a few teeth along the edge and a drawn out point. Leaves may have a purple tinge when young and are placed opposite each other along the stem. Flowers are arranged at the ends of branches, made up of bunches of thin light blue, pink or white flowers covered in fine threads. They produce fine, wind-blown seeds.
Working together to keep our region free from Siam weed
Siam weed grows in tropical and sub-tropical regions with good rainfall. It is dispersed by wind and water, or on clothing, equipment and animals. It loves to take advantage of disturbed areas after storms and spreads quickly to new locations.
We are constantly on the lookout for this weed and need your help to keep our region free of Siam weed.
More information can be found on NSW WeedWise NSW WeedWise – Siam weed or by contacting council’s Biosecurity officer.
