National survey on lookout for inasive Siam weed

A major national survey of one of the world’s most invasive tropical weeds is set to start with nationwide backing.

NSW Department of Primary Industries (DPI) is supporting a new pest plant survey to establish the full extent of Siam weed (Chromolaena odorata) within Australia.

NSW DPI weeds agronomist Bob Trounce said Siam weed infestations are currently known to exist in the Tully, Townsville and Thuringowa areas of north Queensland. At present these infestations are being controlled with an aim of eradication.

“However, Siam weed has the potential to spread into other areas such as northern New South Wales where conditions favour the weed,” Mr Trounce said.

“The cooperation of NSW authorities and communities in the national survey is essential as the potential for the plant to spread includes parts of NSW. Early identification is essential to save costly eradication programs which have been necessary in Queensland.

“The weed is a native of Central America and is now a serious pest weed through many tropical and subtropical countries, including Australia’s neighbours Papua New Guinea and East Timor.”

Siam weed is thought to have arrived in Australia with the movement of heavy equipment, freight or contaminated pasture seed. It is easily spread via people, machinery and animals. Agricultural and horticultural production, forestry plantations and World Heritage Sites are potentially at risk.

“Siam weed has an extremely fast growth rate and is a prolific seed producer. The plant is toxic to stock and has been known to degrade agricultural lands in south-east Asia to the extent that this land has now been abandoned,” Mr Trounce said.

“While Siam weed tends to grow more abundantly along watercourses it has also been found growing on granite hillsides.

“It is an erect or sprawling shrub, forming dense tangled thickets up to six metres high when growing in the open, or up to 20 metres as a climbing vine. Its leaves are almost triangular with a distinctive ‘pitchfork’ three-vein pattern and it can emit a pungent odour when crushed.

“Siam weed’s flowers range from white to a pink mauve and occur in clusters of dense tasselled heads similar in appearance to blue top and Billy goat weed. Flowering occurs predominantly in the May to July period and occasionally in the September to October months in suitable climate and soil conditions.

“As winter months are a major flowering time it is important for people to be on the lookout for this weed.”

Media Contact: NSW DPI weeds agronomist Bob Trounce 02 6391 3156