Siam weed control

Page last updated: Wednesday, 5 February 2020 - 8:53am

Please note: This content may be out of date and is currently under review.

Control methods for Siam weed (Chromolaena odorata) a declared pest in Western Australia.


Information about this pest can be found on the Siam weed: declared pest page.

Chemical requirements

When using any agricultural chemicals please ensure that you always follow instructions on the label and any permit. Users of agricultural chemical products must always strictly comply with the directions on the label and the conditions of any permit. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website.

Chemical control options

Chemical control options can be found below. For other methods of control please refer to the aquatic weed control page, and the declared plant control handbook.

Recommended herbicides

Triclopyr + picloram

Herbicide: Triclopyr + picloram (Group I) (various trade names: see APVMA link)

Active ingredient

300g/L triclopyr + 100g/L picloram

Rates of dilution for spot spraying

1:300 to 1:200

Amount of product/10L water

35mL for plants up to 1.5m tall at flowering

50mL for dense stands greater than 1.5m tall at flowering

Wetting agent

Non-ionic, e.g. BS-1000 @ 10mL/10L


  • A similar product Access™ could also be used, but can only be mixed with distillate
  • A new product Grazon™ Extra in addition to containing picloram + 2,4-D amine has a third herbicide aminopyralid which may give it more activity on woody weeds. Use at 35mL/10L water.

More information and other control methods

Fluroxypyr (333g/L) at 20mL/10L water. Imazapyr and glyphosate also being tested in Queensland.

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080