alert list for environmental weeds
Siam weed or chromolaena – Chromolaena odorata
Current Potential
Siam weed or chromolaena (Chromolaena odorata) Siam weed or chromolaena The problem
Siam weed is on the Alert List for Environmental Weeds, a list of 28 non- native plants that threaten biodiversity and cause other environmental damage. Although only in the early stages of establishment, these weeds have the
potential to seriously degrade – Chromolaena odorata Australia’s ecosystems.
Siam weed is recognised as one of the world’s worst tropical weeds. It has an extremely fast growth rate (up to 20 mm per day) and prolific seed production. In the tropics of Africa and Asia it is a major pest of crops such as coconuts, rubber, tobacco and sugar cane. Some All plants in an infestation of Siam weed flower at the same time. Photo: Colin G. Wilson agricultural areas in South-East Asia have been abandoned because Siam weed plant becomes hard and woody while the has taken over pastures and crops. It is Key points branch tips are soft and green. The leaves also toxic to stock. are arrowhead-shaped, 50–120 mm • Siam weed, one of the world’s worst weeds, Although only present in Australia in long and 30–70 mm wide, with three is established in a few small infestations in a few small infestations in Far North characteristic veins in a ‘pitchfork’ pattern. northern Queensland. Queensland, Siam weed could degrade They grow in opposite pairs along the • It is far more cost-effective to prevent Siam World Heritage-listed rainforests and stems and branches. As the species weed’s spread than to try to control large riverbanks. It also has the potential to name ‘odorata’ suggests, the leaves infestations. increase the fuel load in bushfires, and emit a pungent odour when crushed. • All known outbreaks of Siam weed are being can cause allergic reactions. controlled, with the aim of eradication. Clusters of 10–35 pale pink–mauve tubular flowers, 10 mm long, are found • Siam weed flowers and seeds are conspicuous The weed at the ends of branches. The seeds are during June–July. If you find Siam weed, report dark coloured, 4–5 mm long, narrow it to your state or territory weed management Siam weed has a minimum life span of and oblong, with a parachute of white agency, which will assist in eradicating it. approximately ten years. In open areas hairs which turn brown as the seed dries. it spreads into tangled, dense thickets The root system is fibrous and generally up to 2 m tall, and higher when climbing reaches a depth of 300 mm. up vegetation. Many paired branches grow off the main stem. The base of the 2
Growth calendar Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Flowering Seed formation Seed drop Dieback Regrowth Germination
General pattern of growth 80 mm Siam weed is a perennial species, as it lives for more than one year. It is very well adapted to the wet–dry tropical climate of Australia’s north because its above- The flowers are pink–mauve and tubular; the ground foliage can die off during the dry season (May–October) when virtually no leaves are arrowhead-shaped with serrated rain falls. However, the roots remain alive and the vegetation grows back vigorously edges and veins in a ‘pitchfork’ pattern. during the wet season (November–March). Photo: Colin G. Wilson
Siam weed seeds germinate during the wet season. Seedling growth is prolific, and seedlings that have germinated early in the wet season may flower during the In Australia infestations of Siam weed following flowering season in June–July. Because flowering is triggered by day were discovered in the Tully region of Far length, all plants in an area flower at much the same time of the year. The fruits North Queensland in 1994. One large ripen and drop several months after flowering. infestation had spread down the Tully River – Chromolaena odorata and another was found in pasture in the Bingil Bay area. Other smaller patches How it spreads into India in the 1840s. In particular, were located in the El Arish/Silkwood much of the spread has been attributed areas. These infestations are thought Siam weed spreads mostly through its to the movement of people, equipment to have arisen from contaminated seed numerous seeds – potentially in the and materials during World War II. It is that was brought into Australia from millions in larger bushes – being easily now a serious weed throughout the Indian Brazil in the 1970s. transported short distances by wind due subcontinent and South-East Asia, and to the tufts of hair that catch any breeze. central, western and southern Africa. Where it grows Seeds also readily become lodged in Siam weed is also present in many of
Siam weed or chromolaena Siam weed or chromolaena clothing, animal fur or machinery, and Australia’s near neighbours, including Siam weed grows best in the tropics and in this way Siam weed has spread large East Timor, Philippines, Papua New subtropics, and though not tolerant of distances since initially being introduced Guinea and several Pacific islands. frost it can be found at altitudes up to 1000 m. It grows on most soil types but prefers well drained soils in full sun. It has a competitive advantage over other plants in climates with distinct wet and dry seasons because it survives fires and grows back vigorously following rain.
As an invasive, fast growing plant, Siam
7 mm weed thrives in disturbed areas such as pastures, plantations, clearings, roadsides and riverbanks, particularly those in well-lit sites.
Siam weed is misleadingly named as it is actually a native of Central and northern South America, from Mexico to Brazil. Although first introduced into India as
A parachute of brown hairs helps the seed spread short distances. an ornamental, it has quickly spread Photo: Colin G. Wilson throughout its current range.
Weed Management Guide • Siam weed or chromolaena – Chromolaena odorata 3 1 m
Siam weed invades pastures and crops and has Infestations of Siam weed throughout South-East Asia are potential sources of seed spread into serious impacts on agriculture: West Timor, Australia: West Timor, Indonesia. Indonesia. Photo: Colin G. Wilson Photo: Colin G. Wilson
Why we need to be ‘alert’ • is already present in a few small • has a history of being spread large to Siam weed infestations in Far North Queensland. distances with human activity and Seeds can remain viable in the soil for could easily be reintroduced into other Siam weed poses great risks to Australia’s at least eight years, and therefore parts of the country environment and economy. It: ongoing follow-up work is required • is present in Australia’s neighbours to • outcompetes and smothers crops and • could spread further into very large the immediate north and northeast, native vegetation areas of the productive east coast and and is widespread throughout Asia wet–dry tropics to the north • is toxic to cattle and Africa.
The Alert List for Environmental Weeds
The Federal Government’s Alert List for Environmental Weeds was declared in 2001. It consists of 28 weed species that currently have limited distributions but potentially could cause significant damage. The following weed species are therefore targeted for eradication:
Scientific name Common name Scientific name Common name Acacia catechu var. sundra cutch tree Koelreuteria elegans ssp. formosana Chinese rain tree Acacia karroo Karroo thorn Lachenalia reflexa yellow soldier Asystasia gangetica ssp. micrantha Chinese violet Lagarosiphon major lagarosiphon Barleria prionitis barleria Nassella charruana lobed needle grass Bassia scoparia kochia Nassella hyalina cane needle grass Calluna vulgaris heather Pelargonium alchemilloides garden geranium Chromolaena odorata Siam weed Pereskia aculeata leaf cactus Cynoglossum creticum blue hound’s tongue Piptochaetium montevidense Uruguayan rice grass Cyperus teneristolon cyperus Praxelis clematidea praxelis Cytisus multiflorus white Spanish broom Retama raetam white weeping broom Dittrichia viscosa false yellowhead Senecio glastifolius holly leaved senecio Equisetum spp. horsetail species Thunbergia laurifolia laurel clock vine Gymnocoronis spilanthoides Senegal tea plant Tipuana tipu rosewood Hieracium aurantiacum orange hawkweed Trianoptiles solitaria subterranean Cape sedge
Weed Management Guide • Siam weed or chromolaena – Chromolaena odorata 4
Weed control contacts
State / Department Phone Email Website Territory ACT Environment ACT (02) 6207 9777 [email protected] www.environment.act.gov.au NSW NSW Agriculture 1800 680 244 [email protected] www.agric.nsw.gov.au NT Dept of Infrastructure, Planning and (08) 8999 5511 [email protected] www.nt.gov.au Environment Qld Dept of Natural Resources and Mines (07) 3896 3111 [email protected] www.nrm.qld.gov.au SA Dept of Water, Land and Biodiversity (08) 8303 9500 [email protected] www.dwlbc.sa.gov.au Conservation Tas Dept of Primary Industries, Water 1300 368 550 [email protected] www.dpiwe.tas.gov.au and Environment Siam weed or chromolaena Vic Dept of Primary Industries/Dept of 136 186 [email protected] www.dpi.vic.gov.au Sustainability and Environment www.dse.vic.gov.au WA Dept of Agriculture (08) 9368 3333 [email protected] www.agric.wa.gov.au
The above contacts can offer advice on weed control in your state or territory. If using herbicides always read the label and follow instructions carefully. Particular care should be taken when using herbicides near waterways because rainfall running off the land into waterways can carry herbicides with it. Permits from state or territory Environment Protection Authorities may be required if herbicides are to be sprayed on riverbanks.
The East Timor infestation is of particular significant and lead to a loss of biodiversity. risk of further spread, and the potential concern because of the large numbers To limit escalation of these impacts, it is introduction of new genetic diversity that of defence and non-defence personnel, vital to prevent further introduction of could make future control more difficult.
equipment and vehicles returning to new weed species, such as Siam weed, – Chromolaena odorata There is a high probability of reintroducing Australia from the area. Despite the into uninfested natural ecosystems. Siam weed from infestations throughout vigilance of the Australian Quarantine Early detection and eradication are also South-East Asia, including East Timor, and Inspection Service (AQIS), who are important to prevent the spread of Siam Papua New Guinea and some Pacific actively seeking Siam weed seeds in weed. Small infestations can be eradicated islands. For this reason a vigilant approach equipment and materials as they leave East if they are detected early but an ongoing to surveillance and quarantine in northern Timor and arrive in Australia, there is a commitment is needed to ensure new Australia is required, especially around, very high risk that it will be reintroduced infestations do not establish. but not limited to, military bases. to Australia. Because military exercises are conducted If not quickly eradicated, a new infestation Quarantine is required to in many parts of Australia, Siam weed could rapidly become uncontrollable. prevent further introductions could easily be spread to a remote The Queensland infestation has spread location from military equipment used The importation of Siam weed into only moderately because the climate previously in East Timor. Australia is not permitted because of the there is probably too wet. Under ideal conditions in East Timor, Siam weed has infested virtually the entire country in only 20 years.
What to do about it
Prevention is better than the cure
As with all weed management, prevention is better and more cost-effective than control. The annual cost of weeds to agriculture in Australia, in terms of decreased productivity and management Each seed head can contain hundreds of seeds; even small infestations can potentially produce costs, is conservatively estimated at $4 millions of seeds per year. billion. Environmental impacts are also Photo: Colin G. Wilson
Weed Management Guide • Siam weed or chromolaena – Chromolaena odorata 5
An eradication program for Siam weed in Far North...case Queensland study
In recognition of its potential for Helicopters are used to search for new • continued monitoring and treatment damage throughout northern Australia, infestations during flowering because of infestations by landowners and the current infestations of Siam weed the flowers and maturing seeds are local government. are the target of a nationally funded highly visible from the air. In mid 2003 an infestation of Siam eradication project managed by the Some of the management strategies weed outside the main site was Queensland Department of Natural that are being used to combat the spread reported by a landholder who had Resources and Mines (DNRM). of Siam weed include: previously noticed an unusual plant but Herbicides are sprayed onto patches of not recognised it as Siam weed until he • preventing the use of unsterilised sand Siam weed. Two full-time Strategic Weed saw the television commercial. This from the Tully River Eradication and Education Project staff infestation and several others found at • maintaining strict hygiene standards have been employed to eradicate, monitor the same time were successfully treated for machinery in contact with the and map known infestations, train local by DNRM staff. However, the eradication infestations people and raise public awareness. team are facing a difficult task because • preventing stock movements and the Television commercials are broadcast in the likelihood of eradication is diminished sale of pasture seed from the area prime time and have been particularly if infestations are allowed to flower effective in informing the community • regulating camping and bushwalking and spread seed before being found caseof the threats posed by Siam weed. studyin the area and controlled. – Chromolaena odorata
Mail order seeds are another potential New infestations of Siam Biological control source of infestation. Do not buy seeds weed The potential exists to treat Siam weed via the internet or from mail order Because there are relatively few Siam with biological control agents. A leaf feed- catalogues unless you check with weed infestations, and it can potentially ing moth (Pareuchaetes pseudoinsulata) quarantine first and can be sure that be eradicated before it becomes and a gall fly (Cecidochares connexa) they are free of weeds like Siam weed. have shown some success in controlling established, any new outbreaks should Call 1800 803 006 or see the AQIS Siam weed in Indonesia. Biological control be reported immediately to your state import conditions database agents do not generally eradicate their or territory weed management agency
Apart from its conspicuous flower, which Maps: Data used in the compilation of is present between June and July, Siam actual and potential distribution maps The larvae of the biological control gall fly weed’s leaf, with a pitchfork-style pattern provided by Australian herbaria via (Cecidochares connexa) feed in the stem, which of veins, is quite distinctive. then swells into a gall and harms the plant. Australia’s Virtual Herbarium and Sainty Photo: Colin G. Wilson and Associates P/L, respectively.
Weed Management Guide • Siam weed or chromolaena – Chromolaena odorata Quick reference guide
Identification carpet of off-white seeds on surrounding management agency or local council, vegetation. The Queensland DNRM who will offer advice and assistance on You will first need to confirm its use this natural phenomenon to its control. Because it spreads so easily identity. Contact your state or territory search for new infestations of Siam and poses such a serious threat, its control weed management agency for help in weed from the air should be undertaken with the appropriate identifying the plant. You will need to • leaves are arrowhead or diamond- expertise and adequate resources. take note of the characteristics of the shaped, with serrations on the outer plant in order to accurately describe it. edges and three veins running under- Follow-up work will be Some important features of Siam weed neath the leaf surface in a characteristic required include: ‘pitchfork’ pattern. The leaves give Once the initial infestation is controlled, • flowers are pink–mauve, tubular and – Chromolaena odorata off a pungent odour when crushed. follow-up monitoring and control will about 10 mm long be required to ensure that reinfestation • seeds are spread by the wind, carried by Reporting occurrences does not occur. a parachute of brown hairs. All Siam Once identified, new occurrences of weed plants flower at the same time Siam weed should be reported to the (June–July in Australia), resulting in a relevant state or territory weed
Collecting specimens State or territory herbaria can also identify plants from good specimens. These organisations can provide advice on how to collect and preserve specimens. Siam weed or chromolaena Siam weed or chromolaena State/Territory Postal Address Phone Web Australian National GPO Box 1600 (02) 6246 5108 www.anbg.gov.au/cpbr/herbarium/index.html Herbarium Canberra, ACT, 2601 National Herbarium Mrs Macquaries Rd (02) 9231 8111 www.rbgsyd.nsw.gov.au of New South Wales Sydney, NSW, 2000 National Herbarium Private Bag 2000 Birdwood Avenue (03) 9252 2300 www.rbg.vic.gov.au/biodiversity/herbarium.html of Victoria South Yarra, Vic, 3141 Northern Territory Herbarium PO Box 496 Palmerston, NT, 0831 (08) 8999 4516 http://www.nt.gov.au/ipe/pwcnt/ Queensland Herbarium c/- Brisbane Botanic Gardens (07) 3896 9326 www.env.qld.gov.au/environment/science/herbarium Mt Coot-tha Rd Toowong, Qld, 4066 South Australian Plant PO Box 2732 (08) 8222 9311 www.flora.sa.gov.au/index.html Biodiversity Centre Kent Town, SA, 5071 Tasmanian Herbarium Private Bag 4 Hobart, Tas, 7000 (03) 6226 2635 www.tmag.tas.gov.au/Herbarium/Herbarium2.htm Western Australian Locked Bag 104 (08) 9334 0500 http://science.calm.wa.gov.au/herbarium/ Herbarium Bentley DC, WA, 6983
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