Description: A scrambling woody shrub to 3 metres (higher as a scrambling climber) with distinctive

forked leaf venation and purple flush on new leaves. Clusters of white flowers in May-June and

October are a key identification feature. Distinguished from other weeds Bluetop, Praxelis and Billy

goat weed which all have mauve to purple flowers and are much smaller than Siam weeds’ 1-3 metres

in height.

Distribution: Widespread but localised in the Upper Herbert from Ravenshoe to Blencoe Creek, now

localised and abundant in the middle Herbert River above Abergowrie.

Impacts: This species can form dense thickets and outcompete native species and pasture in both

disturbed and undisturbed sites. Prefers richer soils in alluvial and riparian zones but will grow in rock

and escarpment.

Key projects: Subject of an National Eradication Program up until 2012 now in a transition to

management.

Delimitation

Detailed survey and surveillance is required to ensure Siam weed has not

established outside of the Herbert River Gorge and river channel. Landholders

downstream of Abergowrie to the mouth of the Herbert River should be on the

lookout for Siam weed during peak flowering times during May-June

Prevention

Siam weed produces wind-borne seed which can be easily spread by

machinery, vehicles and stock. Avoiding infested areas is essential for

preventing spread. Stock and agricultural machinery movements from

adjoining core infestation areas in the Upper Herbert, Tully/Murray, Johnstone

or Townsville areas should be managed to ensure they do no increase the

risk.

Asset protection

Siam weed currently occurs in difficult to access gorge and riverine country of

the Herbert River with the densest infestations upstream of Abergowrie.

Integrated control through a combined use of manual removal of single

plants, herbicide control of denser infestations and follow up after fire with

the control of seedlings will reduce the impacts of Siam weed.

Chromolaena odorata (Siam weed) P

rio

rity

D

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Biology x

Peak t

First/last flush p

Occasional y

n/a

Control x

Optimal t

Good p

Marginal y

Not recommended

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1 2 3 4 5

Restricted matter category

6

0.0/5 0.0/5 4.0/5 5.0/5 4.0/5 4.0/5 3.0/5 3.0/5 3.0/5

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flower t x x t p t x t seed p t x x x x x t spray t x x x x x t t t t p p

mechanical y y y y y y y y y y y y cut x x x x x x t t t t t t

burn p t x x x t t

J F M A M J J A S O N D

Restricted matter category

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t A

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Bio

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P

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l Chromolaena odorata (Siam weed)

Control

Spread

What is my biosecurity obligation?

Delimitation Ensure any machinery or vehicles moving from the infested areas are

free from plant material and soil. Spot spray isolated plants and

control isolated infestations. Control plants before seeding and prior

to slashing or disturbance.

Report any suspected plants or infestations to Hinchinbrook Shire

on 07 4776 4607.

Prevention zone

Asset protection

Ensure best practice weed hygiene measures are in place to reduce

risk of spread to new locations. Maintain weed free areas. Identify

high value assets and protect them from impacts where possible.

For more information on management aims in each zone refer to Using the Biosecurity Plan templates

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