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16 November 2007

Chromolaena odorata (Siam weed)

Datasheet Types: Pest, Natural enemy, Tree, Invasive species, Host plant

Abstract

This datasheet on Chromolaena odorata covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.

Identity

Preferred Scientific Name
Chromolaena odorata (L.) R.M. King & H. Rob.
Preferred Common Name
Siam weed
Other Scientific Names
Eupatorium conyzoides Vahl (1794)
Eupatorium odoratum L. (1759)
Osmia odorata (L.) Schultz-Bip.
International Common Names
English
archangel
bitterbush
Christmas bush
chromolaena
chromolaena
siamweed
Spanish
chimuyo
crucito
Eupatorio oloroso
hierba de chiva
paleca
rey del todo
French
Eupatoire odorante
fleurit-Noël
herbe du Laos
Local Common Names
Australia
butterfly-weed
devilweed
hagonoy
jack-in-the-bush
Bangladesh
Assam lata
Cambodia
kântrèang'khaêt
tönöör
Caribbean
bushy thoroughwort
Christmas rose
guérit-tout
guérit-trop-vite
hemp agrimony
jack-in-the-bush
tonka bean
Central African Republic
apollo
bokassa
jabiinde
China
feijicao
Colombia
varejón de caballo
Congo
comilog
diabantou
kalamana
kalamilebe
lantana of Ngouabi
matapa mbala
Rwandais
yhombi
Cuba
rompezaragüey
Côte d'Ivoire
indépendance
sékou touré
Dominican Republic
niquibey
rompesaraguey
El Salvador
chimuyo
Germany
Siam-Kraut
Guam
kesengesil
masigsig
Honduras
crucito
rey del todo
India
ashoke lata
Eupatorium
Sam-solokh
Indonesia
fausse ramie
Siamweed
Laos
nha flang
nroj pawm thsis
Malaysia
fausse ramie
maleanum
pokok german
Mexico
chiguapatzle
cihuapatli
crucito
xtokabal
Micronesia, Federated states of
floss flower
mahsruhsrihk
otuot
wisolmat en rehwei (Pohnpei)
Myanmar
bizat
taw-bizat
Nepal
barnmara
Nicaragua
crucito olorosa
garrapata
Panama
hierba de Chiva
paleca
Peru
chisca
Philippines
agonoi
daladay
devil weed
gonoi
hulohagonoy
huluhagonoi
lahuneri
malasili
talpuspalad
Puerto Rico
cariaquillo Santa Maria
Santa Maria
Saint Lucia
jack in the bush
South Africa
Amstrong's weed
Armstrong weed
eupatorium
isandanezwa
kingsweed
paraffienbos
paraffin weed
parrafinbush
triffid weed
turpentine weed
Sri Lanka
mile-a-minute
United States Virgin Islands
geritoo
Vietnam
co hoi
yên-bach
EPPO code
EUPOD (Eupatorium odoratum)

Pictures

Chromolaena odorata (Siam weed); habit, with flowers. Communist Pacha, Venapacha- in Hyderabad, India. September 2009.
Flowers
Chromolaena odorata (Siam weed); habit, with flowers. Communist Pacha, Venapacha- in Hyderabad, India. September 2009.
©J.M. Garg/via wikipedia - CC BY 3.0
Chromolaena odorata (Siam weed); invasive habit, with flowers. Kadavoor, Kerala, India. December 2009.
Habit
Chromolaena odorata (Siam weed); invasive habit, with flowers. Kadavoor, Kerala, India. December 2009.
©Jeevan Jose/ia wikipdia - CC BY-SA 4.0
Chromolaena odorata (Siam weed); flowering habit. Ghodbunder Road, nr State Highway 42, Maharashtra, India. Deember 2007.
Habit
Chromolaena odorata (Siam weed); flowering habit. Ghodbunder Road, nr State Highway 42, Maharashtra, India. Deember 2007.
©Dinesh Valke/via flickr - CC BY-SA 2.0
Chromolaena odorata (Siam weed); habit, showing leaves.
Leaves
Chromolaena odorata (Siam weed); habit, showing leaves.
Public Domain - Released by Ashasathees/via wikipedia - CC 0
Chromolaena odorata (Siam weed); habit, showing seeds. nr. Kanhanghad, Keral India. May 2017.
Seeds
Chromolaena odorata (Siam weed); habit, showing seeds. nr. Kanhanghad, Keral India. May 2017.
©Vijayan Rajapuram (Vijayanrajapuram)/via wikipedia - CC BY-SA 4.0
Chromolaena odorata (Siam weed); close view of seeds. nr. Kanhanghad, Keral India. May 2017.
Seeds
Chromolaena odorata (Siam weed); close view of seeds. nr. Kanhanghad, Keral India. May 2017.
©Vijayan Rajapuram (Vijayanrajapuram)/via wikipedia - CC BY-SA 4.0
Chromolaena odorata (Siam weed); fruit.
Fruit
Chromolaena odorata (Siam weed); fruit.
©Laurent Gautier
Chromolaena odorata (Siam weed); burning of a C. odorata thicket during the dry season.
Control measures
Chromolaena odorata (Siam weed); burning of a C. odorata thicket during the dry season.
©Laurent Gautier

Summary of Invasiveness

C. odorata is a very widely distributed tropical shrub that is still expanding its range, and is considered one of the world’s worst weeds. It continues to spread due to its effective short- and long-distance dispersal. It can form pure stands where established, often in disturbed areas, grasslands, fallow areas and forestry plantations, and is highly competitive. It is viewed as a major environmental weed, but is appreciated by some agriculturalists as it shortens fallow time in shifting cultivation.

Taxonomic Tree

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Notes on Taxonomy and Nomenclature

Chromolaena odorata has long been referred to as Eupatorium odoratum. It was transferred to the genus Chromolaena by King and Robinson (1970), and although this conception of the tribe Eupatorieae has met some disagreement among botanists, the new binomial of Chromolaenaodorata (L.) R.M. King & H. Rob. is now widely accepted. Nonetheless, references to E. odoratum and even E. odorata are still used today and are common in current literature. A number of additional synonyms in ISSG (2007) cannot be confirmed and are not included here.

Plant Type

Herbaceous
Perennial
Seed propagated
Shrub
Woody

Description

C. odorata is a herbaceous to woody perennial with a bushy habit which forms a very dense thicket about 2 m high, in almost pure stands. This many-branched plant becomes lianescent when it has the opportunity to climb on a support. Isolated individuals start to branch when they reach a height of about 120 cm. After the first year of growth, the plant develops a strong, woody underground storage organ, which can reach a diameter of 20 cm. Stems are terete and become woody. Twigs are slightly striolate longitudinally, pubescent, opposite-decussate. Leaves are simple, opposite-decussate and without stipules. They are rhomboid-ovate to ovate with an acute apex and a cuneate base. The blades are trinerved a few millimetres after the base, roughly crenate-serrate beyond their maximum breadth, slightly pubescent above and pubescent with numerous small yellow dots below (a lens is needed to see this). The petiole is 1-3 cm long, and the blade 5-14 cm long and 2.5-8 cm broad. Leaves and twigs produce a characteristic smell when crushed (Gautier, 1992a). Capitula are grouped in one, three or five convex trichotomic corymbs 5-10 cm in diameter, at the end of the twigs. The involucre is cylindrical, 8-10 mm long by 3-4 mm broad. It is made of a series of four or five oblong bracts, the external being the shorter. These bracts are obtuse, chartaceous, pale in colour with three or five nerves. The receptacle is convex, without scales. There are 15-35 florets per capitulum. The corolla is 5 mm long and has five lobes. Its colour ranges from pale-lilac to white. Styles are of the same colour, exserted and flexuous. Cypselae are composed of a 3- to 4-mm-long fusiform blackish achene, with five beige barbelate ribs, overtopped by a pappus of about 30 barbelate beige capillary bristles which are 4-5 mm long (Gautier, 1992a).

Distribution

C. odorata is often noted as a native of tropical Central and South America, from Mexico and the Caribbean to Brazil; however, the exact northern and southern limits of its native range remain uncertain and are likely to also include some regions outside of the tropics. USDA-ARS (2007) include as part of the native range Texas and Florida (USA), and all South American countries except Chile and Uruguay, and records from Córdoba in Argentina suggest latitudinal limits of approximately 30° North and South. Gautier (1992b) included Uruguay as part of the native range and USA populations as introduced, neither being confirmed in later studies.

Distribution Map

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Distribution Table

This content is currently unavailable.

History of Introduction and Spread

C. odorata was first introduced to Asia to the Calcutta Botanical Garden in the nineteenth century as an ornamental, but had already spread to Malaysia, Sumatra and Indo-China by the 1920s. Burkill (1935) reported that on the Malay Peninsula it was "spreading in from Siam", thus giving rise to its common name in English, ‘Siam weed’. It was first reported from Laos in 1960, and reached the Philippines later in that decade. It carried on spreading through South-East Asia and was reported as growing rampantly in southern Taiwan some decades later (Peng and Yang, 1998).Further spread of C. odorata in South-East Asia and the western Pacific was associated with the movement of military personnel and equipment during World War II. New foci of invasions have been identified as locations where key military bases were established, for instance Rabaul in New Britain and Jayapura in Irian Jaya (McFadyen, 2002). Similarly, troop movement appears to be responsible for the introduction of the weed to East Timor after 1975. It is very likely that much of the spread of the species in Indonesia resulted from the 1960s transmigration programme.In 1994 small infestations of C. odorata were found in Queensland, Australia and it is suspected that the introduction resulted from contaminated pasture seeds from overseas (Waterhouse, 1994). After years of efforts the species can now be viewed as eradicated, but the threat of re-introduction from neighbouring islands is high (Waterhouse and Zeimer, 2002).In West Africa the plant was accidentally introduced with forestry seeds in Nigeria in 1937 and was deliberately introduced to Côte d'Ivoire in 1952 to control Imperata spp. and other coarse grasses following a recommendation by the famous botanist Auguste Chevalier (1952), despite the fact that he regarded the species as a weed (Chevalier, 1949). The current distribution in West and Central Africa extends from Guinea/Sierra Leone (12°W) to central parts of the Democratic Republic of Congo and the Central African Republic, and south to northern Angola (23°E). It was introduced to South Africa near Durban around 1940 and has since spread to Natal, Transvaal, Swaziland and Mozambique.Comparing the distribution of C. odorata with a climatic map and it is clear that all the regions with a suitable environment are not yet invaded, especially in Africa and Oceania. Crutwell McFadyen and Skarrat (1996) predicted the potential distribution using a climate-matching programme, and noted that C. odorata can be expected to invade the following areas in the future:
in West Africa: Sierra Leone, Guinea-Bissau, Gambia, southern Senegal, southern Mali, southern Burkina Faso
in East and Central Africa: southern Sudan, Ethiopia, Kenya, Tanzania, Uganda, Rwanda, Burundi
in southern Africa: Angola, Zambia, Malawi, Mozambique, northeastern Botswana
in the Atlantic Ocean: Fernando Po, Sao Tomé, Annobon
in Arabia: eastern side of Asir, Masquat area
in the Indian Ocean: Comoros, Reunion, and all other islands in the Indian Ocean except Socotra
in the Pacific Ocean: all the islands included in the pentagon: Hawaii, Galapagos, Easter Islands, New Caledonia
in Oceania: Indonesian islands that are not yet affected.
However, Kriticos et al. (2005) revised this model with a more limited estimated potential distribution, predicting that Mediterranean, semi-arid and temperate climates are unsuitable and reducing some inland extensions. However, the revised model supports the earlier conclusions that much of tropical Africa, the northeastern coast of Australia and most Pacific islands are still at risk of invasion.
Another model was used by Raimundo et al. (2007) to predict future spread, and they predicted that four regions are susceptible to Siam weed spread: (1) Central Africa, currently being invaded from the west; (2) southern Africa, spreading north from South Africa, having already reached Swaziland and Mozambique and may extend to East Africa and Madagascar; (3) northern New Zealand and (4) Australia, the latter two at risk from introductions from uncontrolled infestations on several western Pacific islands.

Introductions

Introduced toIntroduced fromYearReasonsIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Côte d'Ivoire 1952 YesNoPossibly introduced from Nigeria, intentional, to control Imperata
Nigeria 1937 YesNoAs a contaminant of forest seed, accidental

Risk of Introduction

In the early 1990s, C. odorata was declared a prohibited species in Australia and became a primary target of weed surveys conducted in northern Australia, Papua New Guinea and eastern Indonesia. When Australian troops were deployed in East Timor in 1999, the Australian Quarantine and Inspection Service instigated an assessment of the quarantine risks associated with movements of troops and equipment between Australia and East Timor, and the risk of introduction of C. odorata seeds was identified as a primary threat. As a result, all equipment and personnel returning to Australia was systematically inspected and cleaned (Waterhouse and Zeimer, 2002). Due the importance of this weed, further intentional introduction is now considered very unlikely; however, further accidental introduction is still highly probable and countries with suitable climates should take all necessary steps to prevent its introduction. It is a declared noxious weed in Hawaii, USA, as well as Australia, and of concern to many other countries.

Means of Movement and Dispersal

Natural Dispersal (Non-Biotic)

The principal means of local spread is via wind dispersal of the abundant small seeds, aided by the fact that each is attached to a ring of hairs thus increasing potential movement in even the lightest of winds.

Vector Transmission

The achenes can readily attach themselves to animal fur and feathers, and thus animal dispersal is probably sometimes responsible for new foci of invasion.
Agricultural Practices

Achenes can be spread by agricultural machinery. Dispersal as a seed contaminant is possible.

Accidental Introduction

There is a high risk of accidental dispersal via movement of machinery, vehicles and people. Seeds can also easily become attached to clothes and thus people can spread seeds unintentionally. There are reports of the impacts military movements have in spreading C.odorata, especially around the Pacific and adjacent countries.

Intentional Introduction

This species is not now considered as an ornamental, though early introductions were made for this reason, such as the first introduction to India in the 1800s.

Pathway Causes

Pathway causeNotesLong distanceLocalReferences
Crop production (pathway cause)Common as a fallow species and probably spread during clearance, also to control ImperataYesYes
Forestry (pathway cause)As a contaminant of forestryYes 
Military movements (pathway cause)Important historically for introductions around the Pacific and neighbouring countriesYes 
Ornamental purposes (pathway cause)Original introductions as an ornamental, now very unlikely to be repeatedYes  
Seed trade (pathway cause)As a seed contaminantYesYes

Pathway Vectors

Pathway vectorNotesLong distanceLocalReferences
Clothing, footwear and possessions (pathway vector)Shoes, in pockets and bagsYes  
Land vehicles (pathway vector)Military vehicles and equipmentYesYes
Livestock (pathway vector)  Yes 
Plants or parts of plants (pathway vector)As a seed contaminantYesYes
Soil, sand and gravel (pathway vector)Assumed as possible meansYesYes 
Wind (pathway vector)Main means of dispersal Yes 

Host Plants and Other Plants Affected

Similarities to Other Species/Conditions

Retief (2002) has found that in southern Africa the genus Mikania shows strong similarity to C. odorata in its distribution, habit, leaf blade outline, floret colour (both have white corollas), capitulum outline and structure of the achene. It is thought that in Australia some plants showing great morphological similarity actually belong to another species found (Waterhouse and Zeimer, 2002).

Habitat

C. odorata can be considered as a major weed in all perennial crops of the humid tropics as well as in forestry. It also invades pastures. Its aggressiveness is much more serious in the Old World tropics where it is an exotic, rather than in its native Americas. C. odorata is found mainly in the humid part of the inter-tropical zone at elevations below 2000 m, in open secondary habitats such as cultivated lands, abandoned or neglected fields, forest clearings, wastelands, along forest trails, fence rows, roadsides and forest margins. Gils et al. (2006) found significant differences in four habitats invaded in KwaZulu-Natal, South Africa, concluding that spread along paths and lack of control in state forest mean that it is most abundant there, followed by eucalyptus plantations, and a low abundance in sugar cane fields and communal grasslands is thought to be due to fires and ground cover.

Habitat List

CategorySub categoryHabitatPresenceStatus
TerrestrialTerrestrial – ManagedCultivated / agricultural landPrincipal habitatHarmful (pest or invasive)
TerrestrialTerrestrial – ManagedCultivated / agricultural landPrincipal habitatProductive/non-natural
TerrestrialTerrestrial – ManagedManaged forests, plantations and orchardsPrincipal habitatHarmful (pest or invasive)
TerrestrialTerrestrial – ManagedManaged grasslands (grazing systems)Principal habitatHarmful (pest or invasive)
TerrestrialTerrestrial – ManagedDisturbed areasPrincipal habitatHarmful (pest or invasive)
TerrestrialTerrestrial – ManagedDisturbed areasPrincipal habitatNatural
TerrestrialTerrestrial – ManagedDisturbed areasPrincipal habitatProductive/non-natural
TerrestrialTerrestrial – ManagedRail / roadsidesSecondary/tolerated habitatHarmful (pest or invasive)
TerrestrialTerrestrial – ManagedRail / roadsidesSecondary/tolerated habitatNatural
TerrestrialTerrestrial ‑ Natural / Semi-naturalNatural forestsPrincipal habitatHarmful (pest or invasive)
TerrestrialTerrestrial ‑ Natural / Semi-naturalNatural forestsPrincipal habitatNatural
TerrestrialTerrestrial ‑ Natural / Semi-naturalNatural grasslandsPrincipal habitatHarmful (pest or invasive)
TerrestrialTerrestrial ‑ Natural / Semi-naturalNatural grasslandsPrincipal habitatNatural
TerrestrialTerrestrial ‑ Natural / Semi-naturalRiverbanksSecondary/tolerated habitatHarmful (pest or invasive)
TerrestrialTerrestrial ‑ Natural / Semi-naturalRiverbanksSecondary/tolerated habitatNatural
TerrestrialTerrestrial ‑ Natural / Semi-naturalScrub / shrublandsSecondary/tolerated habitatHarmful (pest or invasive)
TerrestrialTerrestrial ‑ Natural / Semi-naturalScrub / shrublandsSecondary/tolerated habitatNatural
Littoral Coastal areasSecondary/tolerated habitatHarmful (pest or invasive)
Littoral Coastal areasSecondary/tolerated habitatNatural

Biology and Ecology

Genetics

Genetic variation in invasive populations has been noted. In Australia, two genotypes have been found (Waterhouse and Zeimer, 2002). Von Senger et al. (2000) found that the form of C. odorata occurring in South Africa is morphologically distinct from other investigated material and that more than one genotype exists. Kriticos et al. (2005) also found that the distribution of C. odorata in South Africa extends further south than predicted by their model, based on Asian and American distribution records, which supports the view the South African variety has different climatic requirements. Zachariades et al. (2004) confirmed that South African populations have a northern Caribbean origin, identical to material from Cuba, Jamaica and Puerto Rico.
Physiology and Phenology

Photosynthesis follows the classical C3 pathway (Saxena and Ramakrishnan, 1984). Due to a very efficient strategy in resource allocation, growth is very rapid and six months after germination the plant reaches a height of 2 m, with profuse branching. If the plant finds a support, the main stem can continue its growth and reach a height of 10 m in subsequent years, but generally the main stem bends and lateral branches take up the vertical growth, with further branching. In the first steps of development, the primary root will curve and grow horizontally for a few centimetres. The root system will then branch abundantly, resulting in a very dense but superficial network. After the first year of growth, the horizontal part of the root will develop massively, resulting in a lignified storage organ which can reach a diameter of 20 cm. This storage organ will ensure resprouting if the aerial parts of the plant become damaged. Seedlings can grow extremely rapidly, with growth rates of up to 20 mm per day having been recorded (Hills and Ostermeyer, 2000).

Reproductive Biology

Sexual reproduction can occur at the end of the first growth season (Gautier, 1993). Flowering is seasonal and generally occurs in the dry season. Flowers are visited by various unspecialised insects, but reproduction is often apomictic. Seventy-five days after the first appearance of the flower buds, fruits are ready to be dispersed. Fruit production of 1 ha of C. odorata thicket can reach 1 billion. Most of the seeds enter the soil and build up a seed bank (Epp, 1987) and seeds may survive in the soil for up to 6 years (Waterhouse and Zeimer, 2002) but usually less than a year unless sheltered microsites exist (Witkowski, 2002). Nevertheless, many are dispersed away from the original site, seeds are generally wind-disseminated but they also stick to fur, feather and clothes. Vegetative reproduction by layering can occur, with branches developing adventitious roots if they touch the ground during the growing season. In general terms, germination behaviour is adapted to secondary habitats but depends widely on the population considered (Edwards, 1974), especially with respect to dormancy and the effect of shade. Humidity and temperatures above 20°C enhance germination. Green and far-red light reduce germination, whereas red or white light has a positive effect (Soerohaldoko, 1975; Ambica and Jayachandra, 1980a; Erasmus and Van Staden, 1986). Seed germination in South Africa was between 20 and 46% (Witkowski, 2002). Seedlings often appear in very high densities (>2000 per m²) and very severe intraspecific selection occurs in the first months of growth. Yadav and Tripathi (1981) and Kushwaha et al. (1981) described population dynamics of C. odorata.

Environmental Requirements

C. odorata can grow in areas with an annual rainfall below 1000 mm, provided the dry season is not too long. It is limited to around 2000 m altitude, which might indicate that C. odorata cannot endure frost. It grows on soils ranging from sand dunes to heavy clays (Liggit, 1983). C. odorata is heavily dependent on the availability of light. Its competitive strategy depends largely on rapid plastic responses that can only be achieved through a high productivity dependent on light. The response of C. odorata to fire is complex. It is true that it cannot establish in areas that are burned annually, such as African savannahs. However, if fire becomes erratic, or has a low intensity, C. odorata can develop and form a dense thicket that will even prevent fire in humid years. In dry years, this thicket will burn but the underground storage organ of C. odorata will then ensure rapid regrowth.

Associations

The very high competitiveness of C. odorata is due to various features. The plant develops a group strategy: its massive establishment due to prolific reproduction, together with its fast growth and branching habit, ensures rapid domination and the suppression of other species through competition for resources and mechanical pressure. Under the very dense canopy of a C. odorata thicket, light is scarce and other fast-growing species cannot survive. Slow-growing, shade-tolerant species are regularly bent to the ground by the continuous pressure of the growth of new C. odorata twigs on the upper layer of the thicket (Gautier, 1992a). It has a very efficient root system for the capture of nutrients (Bennet and Rao, 1968), and allopathic effects may also be involved (Ambika and Jayachandra, 1980b; Nakamura and Nemoto, 1993).

Climate

Climate typeDescriptionPreferred or toleratedRemarks
A - Tropical/Megathermal climateAverage temp. of coolest month > 18°C, > 1500mm precipitation annuallyPreferred 
Af - Tropical rainforest climate> 60mm precipitation per monthPreferred 
Am - Tropical monsoon climateTropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))Preferred 
As - Tropical savanna climate with dry summer< 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])Preferred 
Aw - Tropical wet and dry savanna climate< 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])Preferred 
Cf - Warm temperate climate, wet all yearWarm average temp. > 10°C, Cold average temp. > 0°C, wet all yearPreferred 

Air Temperature

ParameterLower limit (°C)Upper limit (°C)
Absolute minimum temperature0 

Rainfall

ParameterLower limitUpper limitDescription
Dry season duration  number of consecutive months with <40 mm rainfall
Mean annual rainfall10003000mm; lower/upper limits

Rainfall Regime

Summer
Winter

Soil Tolerances

Soil texture > light
Soil texture > medium
Soil texture > heavy
Soil reaction > acid
Soil reaction > neutral
Soil drainage > free

List of Pests

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Natural enemy of

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Notes on Natural Enemies

The aggressive nature and competitiveness of C. odorata in the Palaeotropics can be explained by the lack of host-specific natural enemies. In its native range in the Neotropics, it is attacked by a large number of arthropods (Crutwell, 1974; Gagne, 1977) and diseases (Elango et al., 1993; Barreto and Evans, 1994), reviewed by Crutwell McFadyen (1991). The most damaging and those that are promising potential biological control agents are given in the List of Natural Enemies, which includes successful introductions that have already been made. These natural enemies are either host-specific or only attack a narrow range of species related to C. odorata.

The defoliating habit of Pareuchaetes spp. larvae made them the first choice as a biological control agent and they have been studied in most detail. Cock and Holloway (1982) clarified Pareuchaetes taxonomy and showed that there are a series of species present throughout the native range of C. odorata, each with different ecological requirements. Consequently, they recommended matching the climates of areas where biological control of C. odorata was desired with those of Pareuchaetes spp. in order to select the most appropriate species for introduction. Other biological control agents have also been released in Malaysia and Thailand.

Natural enemies

Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Acalitus adoratusHerbivore
Stems
Leaves
  Malaysia 
Actinote anteasHerbivore
Leaves
    
Alternaria zinniae (leaf spot of zinnia)Pathogen     
Anhellia nigerPathogen
Stems
Leaves
    
Anoplocnemis curvipes (giant coreid bug)Herbivore     
Aphis gossypii (cotton aphid)Herbivore     
Aphis spiraecola (Spirea aphid)Herbivore     
Apion brunneonigrumHerbivore
Inflorescence
  Malaysia 
Cercospora eupatoriiPathogen     
Cionothrix praelongaPathogen
Leaves
    
Cremastobombycia chromolaenaeHerbivore    
Fusarium pallidoroseum (fungal gummosis (of Leucaena))Pathogen     
Melanagromyza eupatoriellaHerbivore
Stems
  Thailand 
Mescina parvulaHerbivore
Stems
    
Ophiociliomyces bauhiniaePathogen     
Pareuchaetes aurataHerbivore
Leaves
    
Pareuchaetes pseudoinsulataHerbivore
Leaves
  Africa; Ghana; Guam; Malaysia; Mariana Islands; Micronesia; South Africa; Thailand 
Passalora perfoliataPathogen
Leaves
    
Procecidochares connexaHerbivore
Stems
    
Redbia trichomambustaPathogen     
Septoria ekmanianaPathogen
Leaves
    

Impact Summary

CategoryImpact
Animal/plant collectionsNone
Animal/plant productsNone
Biodiversity (generally)None
Crop productionNone
Economic/livelihoodPositive and negative
Environment (generally)Positive and negative
Fisheries / aquacultureNone
Forestry productionNegative
Human healthNone
Livestock productionNegative
Native faunaNegative
Native floraNegative
Rare/protected speciesNone
TourismNone
Trade/international relationsNone
Transport/travelNone

Impact

C. odorata can be considered as a very serious weed in all types of perennial crops in the humid areas of the Palaeotropics. In low-growing plantations such as coffee and cocoa, C. odorata can completely smother the crop, whereas in taller plantations such as rubber or teak, as soon as the canopy is closed the weed is no longer a problem.

In shifting cultivation, C. odorata replaces the natural secondary succession and becomes the dominant fallow species (De Foresta and Schwartz, 1991; De Rouw, 1991; Gautier, 1992a; Roder et al., 1995; Slaats, 1995). It is often considered as beneficial by local farmers (Baxter, 1995) because it is easier to clear than the secondary vegetation, helps to suppress Imperata cylindrica, and is believed to accelerate the recovery of soil fertility. This last aspect is still a matter of debate among scientists, but there is an increasing requirement for further studies on the influence of the C. odorata fallow system before any biological control programme is launched (Herren-Gemmil, 1991; De Foresta, 1996).

C. odorata causes severe problems in pastures in the Central African Republic (Audru et al., 1988), Java (Indonesia) and the Philippines because it invades overgrazed areas. Due to the high nitrate content of the leaves, C. odorata is poisonous to cattle and generally not grazed (Sajise et al., 1974).

C. odorata can also transmit pathogenic fungi (Vayssière, 1957; Esuruoso, 1971; Oritsejafor, 1986), and act as a host for insect pests including Zonocerus variegatus (Modder, 1984; Chapman et al., 1986), whose nymphs feed on leaves, flowers and fruits in Africa; Aphis citricola and Rhopalosiphum maidis in India; as well as various other polyphagous insects.
In regions where there are dry seasons C. odorata can be a fire hazard (Englberger, 2009).

Impact: Economic

C. odorata can be considered as a very serious weed in all types of perennial crops in the humid areas of the Palaeotropics. In low-growing plantations such as coffee and cocoa, C. odorata can completely smother the crop, whereas in taller plantations such as rubber or teak, as soon as the canopy is closed the weed is no longer a problem.

In shifting cultivation, C. odorata replaces the natural secondary succession and becomes the dominant fallow species (De Foresta and Schwartz, 1991; De Rouw, 1991; Gautier, 1992a; Roder et al., 1995; Slaats, 1995). It is often considered as beneficial by local farmers (Baxter, 1995) because it is easier to clear than the secondary vegetation, helps to suppress Imperata cylindrica, and is believed to accelerate the recovery of soil fertility. This last aspect is still a matter of debate among scientists, but there is an increasing requirement for further studies on the influence of the C. odorata fallow system before any biological control programme is launched (Herren-Gemmil, 1991; De Foresta, 1996).

C. odorata causes severe problems in pastures in the Central African Republic (Audru et al., 1988), Java (Indonesia) and the Philippines because it invades overgrazed areas. Due to the high nitrate content of the leaves, C. odorata is poisonous to cattle and generally not grazed (Sajise et al., 1974).

C. odorata can also transmit pathogenic fungi (Vayssière, 1957; Esuruoso, 1971; Oritsejafor, 1986), and act as a host for insect pests including Zonocerus variegatus (Modder, 1984; Chapman et al., 1986), whose nymphs feed on leaves, flowers and fruits in Africa; Aphis citricola and Rhopalosiphum maidis in India; as well as various other polyphagous insects.

Impact: Environmental

Impact on Habitats

Depending on the length and the intensity of the dry season, C. odorata represents a serious fire hazard because of the presence of volatile oils in stems and leaves. Uncontrolled fires can destroy plantations, villages and infested natural vegetation. This problem is particularly acute in Natal, South Africa, where C. odorata is reported to burn even when green in the growing season (Macdonald, 1983).

Impact on Biodiversity

C. odorata invades natural vegetation such as forest margins and savannahs in Africa (Macdonald, 1983, Macdonald and Frame, 1988; Gautier, 1992a, 1996). In South Africa it is posing a very serious threat to the continued survival of the Nile crocodile (Leslie and Spotila, 2001).

Threatened Species

Threatened speciesWhere threatenedMechanismsReferencesNotes
Crocodylus niloticus
South Africa
  

Impact: Social

In some regions, such as southwestern China, the appearance of C. odorata has allowed a shortening of fallow periods in shifting cultivation and thus the species is welcomed by these traditional agriculturalists (Momose, 2002).

Risk and Impact Factors

Invasiveness

Proved invasive outside its native range
Has a broad native range
Abundant in its native range
Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
Pioneering in disturbed areas
Highly mobile locally
Benefits from human association (i.e. it is a human commensal)
Fast growing
Has high reproductive potential
Has propagules that can remain viable for more than one year
Reproduces asexually

Impact outcomes

Ecosystem change/ habitat alteration
Modification of fire regime
Modification of nutrient regime
Modification of successional patterns
Monoculture formation
Negatively impacts agriculture
Negatively impacts forestry
Negatively impacts livelihoods
Reduced native biodiversity
Threat to/ loss of endangered species
Threat to/ loss of native species

Impact mechanisms

Causes allergic responses
Competition - monopolizing resources
Competition - shading
Competition - smothering
Poisoning
Rapid growth
Rooting

Likelihood of entry/control

Highly likely to be transported internationally accidentally
Difficult to identify/detect as a commodity contaminant
Difficult/costly to control

Uses

A very important though facultative use of C. odorata is as a green manure or fallow component. Being invasive, it has replaced native secondary successional species in much of the tropical Old World, and farmers have learnt to live with as a component of the farming system, especially in shifting cultivation and rotational practices. It is often preferred over native species as it easier to cut and clear, and is observed to suppress another invasive species, Imperata cylindrica, which has much worse impacts on agriculture. Reports that C. odorata improves soil fertility require confirmation, though clearly the fallow period will have a positive effect. C. odorata can also be cut and cleared prior to seed set, composted and used as a valuable organic soil amendment. It is generally regarded as poisonous to animals and thus not recommended as a livestock feed. However, some studies show its benefits in low concentrations, such as up to 5% for egg-laying chickens which also improved yolk colour (Fasuyi et al., 2005).
In Malaysia, where C. odorata is an invasive exotic, plant parts are used by traditional practitioners for treatment of burns, wound healing, skin infections, post-natal wounds, and as an anti-malarial (Nurul Huda et al., 2004). Several medical studies have confirmed that leaf extracts have certain anti-microbial, anti-inflammatory and wound-healing effects, and are identified as a potential source of human medicines.

Uses List

Environmental > Soil conservation
Environmental > Soil improvement
Materials > Fertilizer
Medicinal, pharmaceutical > Source of medicine/pharmaceutical
Fuels > Fuelwood
Animal feed, fodder, forage > Fodder/animal feed

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Control

Cultural control

Slashing C. odorata stems manually or mechanically is not a solution, because the plants coppice profusely from the roots. The root itself must be dug out, which can sometimes be done by hand if the soil is moist, or by mechanized equipment. This type of control must be conducted at least twice during the growing season (Liggit, 1983; Audru et al., 1988; Muniappan and Marutani, 1991). Cultural practices involving other competitive species have been proposed: using Leucaena leucocephala in pastures in the Philippines (Castillo et al., 1977); Tephrosia purpurea in cocoa plantations in Sri Lanka (Salgado, 1972); and signalgrass (Brachiaria decumbens) in Yunnan, China (Wu and Xu, 1991). For perennial plantations, a ground-cover crop such as Pueraria phaseoloides, Calopogonium mucunoides, Centrosema pubescens or Vigna unguiculata can control C. odorata in the first years, before the crop canopy is closed (Liggit, 1983; Audru et al., 1988; Muniappan and Marutani, 1991). In South Africa, an annual burning regime can effectively control the plant in grassland situations by killing mature plants and preventing new seedlings from establishing (Goodall and Zachariades, 2002).

Mechanical control

Seedlings and young plants can be removed by hand-pulling, but follow-up clearance every 2-3 months is necessary because of rapid regrowth (Zachariades and Goodall, 2002).

Chemical control

C. odorata is most susceptible to chemical control when it is growing vigorously, such as at the beginning of the rainy season. Best control is usually obtained when herbicides are applied to young shoots after slashing. For control of germinating C. odorata, pre-emergence herbicides may be used, such as diuron or metribuzin in yams and cassava, oxyfluoren in cassava, cyanazine+atrazube or atrazine+terbutryn in maize, and dipropetrin in groundnuts and cotton, The following may be used as post-emergence treatments: 2,4-D; glyphosate; asulam; paraquat; triclopyr; imazapyr; metsulfuron; tebuthiuron; atrazine (which also inhibits germination); picloram and classical combinations such as picloram+2,4-D; dicamba+2,4-D. Some of these, such as 2,4-D, atrazine and paraquat, are only likely to be effective on seedlings or young plants. For mature plants, glyphosate or combinations including picloram, dicamba or triclopyr will be needed, and even then, repeat treatments are likely to be necessary. More detailed suggestions for the use of herbicides are provided by Ikuenobe and Ayeni (1998). Ferrar et al. (1998) provide a valuable update on many aspects of controlling this weed. Vermeulen et al. (1996) give the latest South African recommendations including use of granular formulations of tebuthiuron and cut stump treatments with imazapyr and triclopyr. In Australia the herbicides used are picloram + triclopyr or fluoxypyr, in combination with a wetting agent. Picloram + triclopyr were used where a residual action is desired (Waterhouse and Zeimer, 2002).

Biological control

As C. odorata is found in forests, pastures and on wasteland as well as in arable areas, biological control is an attractive approach, especially where use of herbicides is uneconomic. Biological control in the Neotropics was pioneered by the Commonwealth Institute for Biological Control [IIBC] in the mid-1970s and work has been continued by other agencies, notably research teams from South Africa and Australia. Pareuchaetes pseudoinsulata was selected as the first agent for trial in West Africa and has been widely released there, in South and South-East Asia and the Pacific. Initial results were disappointing because establishment was hampered by poor climatic matching and predation of the larvae feeding exposed on the leaves. Although establishment took place readily in Sri Lanka and Sabah (Malaysia), P. pseudoinsulata did not build up in sufficient numbers to have any beneficial impact, but when it was released in Guam, C. odorata was suppressed (Muniappan et al., 1988; Seibert, 1989). This difference in performance on small islands and larger land masses is attributed to the lower level of predation on small islands. Attempted introductions of the inflorescence-feeding weevil, Apion brunneonigrum, in West Africa and in Asia were impeded by the need to send field-collected adults because no successful mass-breeding technique had been developed. None was successful. Incidentally, the weevils released in Sabah were contaminated by the gall mite Acalitus adoratus, which became established and has spread widely in the region (Crutwell McFadyen, 1995). This mite is known to be completely host specific and presents no threat although the damage it does is too slight to have a major impact on C. odorata. A regional co-operative programme in South-East Asia started in 1993 made the first introductions of the stem gall fly, Cecidochares connexa [Procecidochares connexa], which is now established in most Indonesian islands and gives good control of the plant 4-5 years after release (Chiu et al., 2005). McFadyen (2002) reported that the fly was cleared for release in Papua New Guinea, while the release permit is awaited in the Philippines and Guam. The moth Pareuchaetes pseudoinsulata is now widely established in northern Sumatra (Indonesia), and in some sites in northern Papua New Guinea. A butterfly, Actinote anteas, which also attacks a closely related invader Mikaniamicrantha, has been released in Indonesia but its successful establishment has yet to be confirmed. In West Africa, Paraeuchaetes pseudoinsulata has been successfully established and there is an ongoing programme in South Africa. However, the strain of C. odorata found there is different to that in Asia and elsewhere in Africa, and it is proving difficult to find agents that will attack it. Nonetheless, recent studies confirm the potential of Lixus aemulus, a stem-boring weevil imported from Brazil, in reducing biomass and seed production (Kluge and Zachariades, 2006).
McFadyen (1996) reviewed the situation to the early 1990s and more recent progress in biological programmes and future plans throughout the tropics have been reviewed in Zachariades et al. (2002), and more recent reviews include Strathie and Zachariades (2004) and LiHua and YuLong (2007).

Integrated control

In view of the limited success achieved with released biological control agents and the difficulty in preventing the spread of C. odorata, integrated control strategies are being explored. These include either excluding fire (coastal forest sites), or using fire prior to seed release to kill plants and soil-stored seeds immediately prior to seed production, together with chemical and/or physical clearing (Witkowski, 2002). The quest for effective control agents is also being pursued and a sustained effort to maintain people's awareness is also seen as a key factor in any management programme (Zachariades and Goodall, 2002). In Australia, herbicide application, hand-pulling or fire are often used in combination depending on local site conditions (Waterhouse and Zeimer, 2002).

Links to Websites

NameURLComment
Chromolaena odoratahttp://www.arc.agric.za/home.asp?pid=5229This website acts as a portal of the Working Group on Chromolaena odorata, a working group under the International Organization for Biological Control of Noxious Plants and Animals (IOBC). Other invasive Eupatorieae are also covered.
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.
Global register of Introduced and Invasive species (GRIIS)http://griis.org/Data source for updated system data added to species habitat list.

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  • Global spatial distribution of Chromolaena odorata habitat under climate change: random forest modeling of one of the 100 worst invasive alien species, Scientific Reports, 10.1038/s41598-023-36358-z, 13, 1, (2023).

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