Scientific name
Chromolaena odorata (L.) R. M. King & H. Robinson
Common name
Siam weed
Khmer/Indigenous name
kântrèang’khaêt; tönöör
Family
Asteraceae
Plant type
Dicot
Description/ Characteristics
An upright (erect) or sprawling shrub forming thickets and usually growing 1.5 to 3 m tall in the open. However it may reach greater heights (6-20 m) when climbing over trees and other taller vegetation.The slender stems are generally yellowish-green and somewhat hairy (pubescent), but become woody towards the base of the plant. These stems grow up to 7 m or more in length and several are usually produced from the plants long-lived root-stock (crown). They are much-branched, with the side (lateral) branches usually being produced in pairs in the leaf forks (axils).The oppositely arranged leaves (5-12 cm long and 3-7 cm wide) are triangular or egg-shaped in outline with broad end at base (ovate) and have a pointed tip (acute apex). They are hairy (pubescent) on both surfaces and have coarsely toothed (serrated) margins. These leaves are borne on stalks (petioles) up to 6 cm long (usually 10-15 mm), and give off a strong odour when crushed.The small flower-heads (capitula) do not have any ‘petals’ (ray florets) and are borne in dense clusters at the ends of the branches (in terminal panicles). These flower-heads (about 10 mm long and 3 mm wide) are pale pink or pale mauve in colour (sometimes appearing whitish when older) and consist of numerous (15-30) tiny flowers (tubular florets). These tiny flowers (10-12 mm long) are surrounded by several layers of overlapping slender bracts (an involucre) 8-9 mm long. Each flower-head (capitulum) is borne on a stalk (peduncle) 10-30 mm long.
Habitat – Biology
It grows on soils ranging from sand dunes to heavy clays along roadsides and in wastelands. It can be found growing on bunds around rice fields but not likely to persist in the rice field itself. Siam weed produces huge numbers of windborne seeds within 8–10 weeks after flowering. Siam weed dies back in the dry season but re-shoots after rain.
Control methods
Mechanical control: Physical removal of the basal/root ball is very effective.
and recommended for smaller infestations. However, it is
extremely important to make sure the removed plant does
not remain in contact with soil, as any contact will result
in the plant re-shooting.
Chemical control: Herbicide application, such as Glyphosate, at the correct rates, and before flowering, will provide effective control if carried out
regularly. Incorrect application can lead to herbicide pruning,
which will allow the plant to re-shoot. Always read the label
before using any herbicide.
http://www.cabi.org/isc/datasheet/23248
More info:
http://www.knowledgebank.irri.org/step-by-step-production/growth/weed-management
Image copyright
Dr Robert J. Martin
University of Sydney
bob.martin@sydney.edu.au
WeedID Project 