AGP - Chromolaena odorata
 

CHROMOLAENA ODORATA (L.) R.M. King & H. Robinson 

 

 

 

Family: Asteraceae Synonyms: Eupatorium odoratum L.

Common names: Siam Weed, Bitter bush, Herbe du Laos, Feijiçao.

A perennial scrambling shrub, growing up to a height of 5 m when support is available. The shoots dry up after flowering in December-January in the Northern Hemisphere, coinciding with the dry season, and become a fire hazard. The pithy dry stems readily burn but the stumps remain alive. When most vegetation in an area is killed by fire, the stumps of C. odorata sprout immediately after the first rain and become a dominant vegetation in the area. Branches of plants scramble and often individual plants occupy areas up to 5 m in diameter.

It is highly allelopathic and suppresses neighboring vegetation by releasing chemicals that are toxic.

C. odorata harbours pests such as Aphis spiraecola Patch. Brachycaudus helichrysi (Kltb.) and Aphis fabae Scopoli. It serves as a non-nutritional source to the serious pest, Zonocerus sp. in W. Africa by providing pyrrolizidine alkaloids and can encourage an eventual population build-up. It grows in many soil types but prefers well-drained soils. It does not tolerate shade and thrives well in open areas.

C. odorata is seasonal and produces thousands of seeds per plant during January to March in the northern hemisphere. Seeds are dispersed by wind.

Manual slashing, use of bush-cutter or tractor-drawn implements are commonly used methods of control. Slashing causes rapid regeneration unless followed by other methods to suppress this weed for an extended period. Manual weeding is labour intensive. Use of tractor drawn equipment is limited to areas that are accessible.

Use of cover crops such as Centrosema pubescens Benth., Pueraria phaseoloides (Roxb.) Benth. Calopogonium muconoides Desv., Desmodium ovalifolium Guill. & Perr. and Tephrosia purpurea (L.) have been recommended to prevent or reduce the incidence of C. odorata in plantation crops. In the southern part of China, use of the pasture grass, Brachiaria decumbens Stapf has been reported to reduce the infestation of the pastures by C. odorata.

Chemical control using herbicides applied at the seedling stage or on early regrowth has given encouraging results. Triclopyr has proven to be the most effective. However, problems in herbicide use include (a) the high cost of the chemicals and their application, (b) ecological concerns and, (c) non-compatibility in many cropping and other environmental situations.

Biological control is a promising method that has been vigorously pursued by various organizations in the world to tackle this weed. The plant's natural enemy (Pareuchaetes pseudoinsulata Rego Barros (Lepidoptera:Arctiidae) introduced and established in Guam, Rota, Tinian, Saipan and Pohnpei has given encouraging results in suppressing this weed. This insect is currently reared in Yap, Belau, Kosrae, Indonesia, South Africa, Ghana and Ivory Coast for field establishment. Other natural enemies currently being investigated are Mescinia parvula (Zeller) (Lepidoptera: Pyralidae), Pareuchaetes aurata, Pareuchaetes insulata (Walker) (Lepidoptera: Arctiidae), Actinote anteasDoubleday (Lepidoptera: Acraeidae). Rhodobaenus cariniventris Champ.(Coleoptera:Curculionidae) and the fungal pathogens Septoria ekmaniana Petrack & Cif. (Deuteromycotina: Coelomycetes) and Cionothrix praelonga Wint. (Arthur) (Basidiomycotina: Uredinales.

The most effective biocontrol has been obtained with the release of Pareuchaetes pseudoinsulata in Guam. The best results are achieved with the release of 500 moths or 2000 larvae. Release should be done repeteadly. It is preferable o release the insect at night.

C. odorata is a problem in pasture lands, disturbed forests, roadsides, waste lands, fence rows, river banks, reserve forests, plantations of coffee, tea, teak, rubber, cocoa, oil palm, citrus, cashew, coconut and fields of rice, cotton, sugarcane, tobacco.

C. odorata is a native of tropical central and south America. It was introduced to Asia in the middle of the 1800s, to Africa in 1937 and to Micronesia in the 1960s.

 

Countries: Benin, Central African Republic, Cameroon, Côte d'Ivoire, Ghana, Indonesia, Papua New Guinea, Thailand, Vietnam

 

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