Solanum mauritianum (Bugweed)

Scientific name

Solanum mauritianum Scopoli

Synonyms

Solanum auriculatumAiton

Common names

Bugweed, bug berry, bug tree, bugtree, earleaf nightshade, flannel leaf, kerosene plant, tobacco bush, tobacco weed, tree tobacco, wild tobacco, wild tobacco bush, wild tobacco plant, wild tobacco tree, woolly nightshade.

Family

Solanaceae

Origin

Native to South America (Brazil, Uruguay and northern Argentina).

Naturalised distribution (global)

Locations within which Solanum mauritianum is naturalised include Australia, southern Europe, tropical and southern Africa, southern USA and in many oceanic islands with warm climates.

Introduced, naturalised or invasive in East Africa

Solanum mauritianum is invasive in parts of Kenya (A.B.R. Witt pers. obs.) and Uganda (Haysom and Murphy 2003) and it is present in Tanzania (A.B.R. Witt pers. obs.). It is particularly problematic in Uganda in degraded forests and its control is going to very costly as more forests become degraded abetting its further spread.

Habitat

Agricultural areas, coastland, natural forests, planted forests, forest margins, riparian zones (banks of watercourses), ruderal/disturbed, urban open spaces. It is tolerant of many soil types.

Description

Solanum mauritianum is a large shrub or small tree usually growing 1.5-4 m tall but sometimes up to 10 m. It has a life of up to thirty years.

Its large oval leaves are grey-green in colour and covered with felt-like hairs. One or two ear-shaped leafy structures are usually present at the base of the leaf stalks.

The flower is purple with a yellow centre are produced in dense branched clusters. The plant can flower year round. Its fruit are yellow globular berries (10-15 mm across).

S. mauritianum is a favoured food plant of the African olive-pigeon (Columba arquatrix). It is poisonous for many other organisms, including humans (Olckersa and Zimmermann 1991).

Reproduction and dispersal

Spread from seed in dumped garden waste, and dispersed by birds.

Similar species

Quite distinctive in its size. There are smaller purple-flowered native nightshades (Solanum species), of which the most similar are Solanum stelligerum (devil's needles) and Solanum densevestitum. These also have furry grey-green leaves, but they are smaller and narrower, and the plants are usually only 1m high. S. stelligerum usually has some prickles scattered on the stems, as do most native nightshades found on the south coast, but S. densivestitum does not.

Two native shrubs or small trees, both typical of moist areas such as gullies and rainforest edges, can have large densely furry leaves, particularly on new growth. They are Clerodendrum tomentosum, whose leaves often have a purple leaf stalk, and Astrotricha latifolia, whose leaves are often held at an angle of nearly 90° to the leaf stalk. The upper leaf surface is green and glossy but the lower surface, leaf stalk and new growth is matted with clumps of soft woolly hairs.

Economic and other uses

Solanum mauritianum can be grown as a nursery plant. However, this use cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

Solanum mauritianum can form dense stands that inhibit the growth of other species through overcrowding and shading. All parts of the plant are toxic to humans, especially the green berries. The fine hairs on the leaves can be an irritant.

S. mauritianum has been included in the Global Invasive Species Database (GISD 2006). 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) and Australia.

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. 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.

Small plants may be hand-pulled but mature plants will re-sprout if they are cut down. Solanum mauritianum is easily killed with herbicides applied as foliar, basal bark (painting herbicide onto the bark) or cut stump applications. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

Biological control has been instituted in South Africa, with the release of a sap-sucking lace bug (Gargaphia decoris) in 1999.

Legislation

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

References

CABI Invasive Species Compendium online data sheet. Solanum mauritianum (tree tobacco). CABI Publishing 2011. www.cabi.org/ISC. Accessed March 2011.

GISD (2006). Global Invasive Species Database online data sheet. Solanum mauritianum (tree, shrub). www.issg.org/database. Accessed March 2011.

Haysom, K.A. and Murphy, S.T. (2003).The status of invasiveness of forest tree species outside their natural habitat: a global review and discussion paper. Forest Health and Biosecurity Working Paper FBS/3E. Forestry Department. FAO, Rome (unpublished).  www.fao.org/docrep/006/j1583e/j1583e00.htm.

Henderson, L. (2001).  Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa.  Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.

Olckers, T. and Zimmermann, H.G. (1991). Biological control of silverleaf nightshade, Solanum elaegnifolium, and bugweed, Solanum mauritianum, (Solanaceae) in South Africa.  Agriculture, Ecosystems and Environment, 37(1-3):137-155.

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: eafrinet@africaonline.co.ke