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Siam weed
Pest alert
If you have seen this plant
Call QPIF 13 25 23
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- Dying flowers of Siam weed
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- Siam weed flowers
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- Siam weed plant
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- Siam weed seedling
General information
Siam weed (Chromolaena odorata) is a Class 1 declared pest plant in Queensland. Class 1 pests are subject to eradication from the state. Landowners must take reasonable steps to keep land free of Class 1 pests. It is a serious offence to introduce, keep or supply a Class 1 pest without a permit issued by the Department of Primary Industries and Fisheries. Penalties of up to $60,000 apply.
Siam weed is considered one of the world's most invasive weeds. It is the target of a nationally funded eradication program.
Overview
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Scientific name |
Chromolaena odorata |
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Impacts |
- quickly invades and smothers native vegetation
- out-competes pastures, crops, and native vegetation
- causes skin problems and asthma in allergy-prone people
- increases frequency and intensity of bushfires
- poisons stock
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Description |
- grows as a dense, tangling bush to 2-3 m
- scrambles up trees to 20 m
- root system is fibrous and shallow in most soils
- develops an enlargement at the junction of stem and root, called a basal ball
- leaves are soft, green, hairy and roughly triangular in shape with a distinctive 'pitchfork' three-vein pattern
- new leaf growth can have purple colouration
- leaves emit a distinctive odour when crushed
- stems are smooth, round and fairly brittle, becoming woody at the base when old
- produces masses of pale lilac flowers, appearing white from a distance
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Habitat/distribution/life cycle |
- suited to highly productive land types
- grows easily along watercourses, foreshores and swamps
- generally found in areas with rainfall over 600 mm per annum
- found in the Townsville City Council, Charters Towers Regional Council, Cassowary Coast Regional Council, Cairns Regional Council and Tablelands Regional Council areas
- produces large numbers of windborne seeds (more than 80,000 seeds per plant per season)
- grows at a rate of 20 mm per day or 5 m per year
- dies back in the dry season but reshoots after rain
- grows back quickly after fire, slashing or chemical pruning
- most seeds germinate after rain, although some appear to remain dormant for several years
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Control |
- apply registered chemicals at correct rates
- for smaller infestations remove basal/root ball. Ensure vegetative pieces are not left in contact with the ground where they can reshoot
- see the siam weed fact sheet for further information on control, including registered chemicals and application rates
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Declaration details |
- a declared Class 1 plant under the Land Protection (Pest and Stock Route Management) Act 2002
- importation, possession and sale is prohibited
- landowners are required by law to keep their land free of this plant
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Further information |
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