Scientific name

Ageratum conyzoides  L.

Synonyms

A. conycoides  L.; A. obtusifolium Lam.; Cacalia mentrastoVell.

Common names

Billygoat weed, ageratum, invading ageratum, chickweed, goatweed, adwolo (Lango), kimavi cha kuku (Kiswahili), gathenge (Kikuyu).

Family

Asteraceae (Compositae)

Origin

Central and South America and the West Indies

Naturalised distribution (global)

Locations within which Ageratum conyzoides is naturalised include Asia and temperate Brazil (outside its native range) and throughout Africa except for arid areas.

Introduced, naturalised or invasive in East Africa

Ageratum conyzoides is invasive in parts of Kenya, Tanzania and Uganda (CABI Invasive Species Compendium, G.W. Howard pers. com).It is widespread along roadsides and other disturbed areas, especially where it is damp.

Habitat

Ageratum conyzoides commonly grows in the proximity of habitation, thrives in any garden and agricultural soils and is very common in disturbed sites and degraded areas. It invades forest, woodland, grassland, cultivated land, riparian zones (banks of watercourses), wetlands and coastal dunes. A. conyzoides is an important weed of plantation crops and overgrazed pastures.

Description

Ageratum conyzoides is an erect, branching, soft, slightly aromatic, annual herb with shallow, fibrous roots. It grows to approximately 1 m in height. The stems and leaves are covered with fine white hairs; the leaves are egg-shaped with broad end at base (ovate) up to 7.5 cm long.

The flowers are purple, blue, pinkish or white, less than 6 mm across, with around 30 to 50 flowers and arranged in close terminal flower-heads. The fruits are small brown one-seeded achenes fruits.

Reproduction and dispersal

This species reproduces mainly by seed which are dispersed on the hairs of livestock and wild animals, clothes and agricultural machinery. It can complete its lifecycle (germination to flowering) in less than two months. The seeds germinate in response to light (are photoblastic) and are often no longer viable within 12 months.

Similar species

Ageratum conyzoides is often confused with Ageratum houstonianum (blue billygoat weed). These species can be distinguished as follows:

• Ageratum conyzoides has only a few hairs on the bracts surrounding its flower-heads (the involucral bracts are glabrous or sparsely pubescent). Each of the tiny flowers (florets) which make up the flower-heads have two long and narrow projections (style branches) that are about 5 mm long. The bases of the flower-heads are relatively large (5-8 mm across).
• Ageratum houstonianum has numerous sticky hairs on the bracts surrounding its flower-heads (the involucral bracts are glandular pubescent). Each of the tiny flowers (florets) which make up the flower-heads have two short and narrow projections (style branches) that are about 1-2 mm long. The bases of the flower-heads are relatively small (3-6 mm across).

Economic and other uses

Ageratum conyzoides was originally introduced as a garden plant (and probably as a contaminant with other garden plant seeds) is widely utilised in traditional medicine systems wherever it grows (Okunade 2002). In Africa, A. conyzoides is used to treat fever, rheumatism, headache, colic, wounds caused by burns, dyspepsia, eye problem, uterine disorders and pneumonia. While in Kenya East Africa, it is used in traditional medicine for antiasthmatic, antispasmodic and haemostatic effects (Sharma and Sharma 2001; Okunade 2002). However, these uses cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

Ageratum conyzoides is an important weed in all crops in the tropics and subtropics apart from those under deep shade. It is often one of the first species to colonise degraded areas and so able to prevent other plants from establishing. It is also an alternative host of some economically important crop pathogens and nematodes. Its competitive ability impacts upon native biodiversity and it is also poisonous.

A. conyzoides has been included in the Global Invasive Species Database (GISD 2003). It has been listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment).

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. As Ageratum conyzoides is so widespread this is unlikely to be possible in many instances.

If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

As a common agricultural weed, it is managed in small and large cropping situation by tillage and can contribute to soil fertility as a mulch.

Short periods of flooding can be used to control this weed. As a shallow rooter it is easy to remove by hand at low densities. A wide range of herbicides are available for its control. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

The editors know of no biological control agents available for the control of Ageratum conyzoides.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

References

Bromilow, C. (2001). Problem Plants of South Africa. A guide to the identification and control of more than 300 invasive plants and other weeds. Briza Publications, Pretoria, 258pp.

GISD (2006). Global Invasive Species Database online data sheet. Ageratum conyzoides (herb). www.issg.org/database. Accessed March 2011.

Okunade A. L. (2002). Ageratum conyzoides L. Asteraceae. Fitoterapia 73: 1-16.

CABI invasive species compendium online data sheet. Ageratum conyzoides (billy goat weed). CABI Publishing 2011. www.cabi.org/ISC. Accessed March 2011.

Sharma K and Sharma O.P. (2001). Analysis of precocenes in the essential oil of Ageratum spp. by reverse-phase high-performance liquid chromatography. Phytochem Anal. 12(4): 263-5.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: [email protected]