Opuntia engelmannii (Prickly Pear Cactus)

Scientific name

Opuntia engelmannii Salm-Dyck ex. Engl.

Synonyms

Opuntia lindheimeri Engelm.; Opuntia tardospina Griffiths

Common names

Prickly pear cactus, Engelman's prickly pear, Cactus apple, cow's tongue cactus

Family

Cactaceae

Origin

North and Central America

Naturalised distribution (global)

Locations within which Opuntia engelmannii is naturalised include southern and eastern Africa.

Introduced, naturalised or invasive in East Africa

Opuntia engelmannii is invasive in parts of Kenya including Loisaba in northern Kenya.. The editors are not aware of any records of this species in Uganda and Tanzania, though this does not necessarily mean that it is absent from these countries.

Habitat

Sandy and gravelly soils, semi-arid areas and savanna.

Description

Opuntia engelmannii is a succulent branched shrub that grows up to 1.5 m tall.

The pads (cladodes) are grey-green, egg-shaped in outline but with the narrower end at the base (obovate) to round, about 15-30 cm long and 12-20 cm wide. The yellow to white spines, mainly found in the top half of the cladode, are up to 6 cm long, slightly curved and very hard.

The flowers are yellow, occasionally reddish, funnel-shaped, 5-8 cm in diameter and about the same in length.

The plant bears purple fleshy fruits that are 3-7 cm long. The fruit is edible.

Reproduction and dispersal

Opuntia engelmannii reproduces by stem fragments (stem segments may become dislodged and produce roots) and also by seeds.

Economic and other uses

Opuntia engelmannii is cultivated as an ornamental or as live hedge and the fruit is edible. However, these uses cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

Opuntia engelmannii is a weed of pasture land and The spines can injure people, livestock and wild herbivores. The plant lowers the value of pastures and it also curtails movement of grazing animals. It displaces native species and prevents the free movement of wildlife.

O. engelmannii (under the name of Opuntia lindheimeri) 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 in most Australian states.

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.

Manual control can be effective when numbers of plants are very low but must be done carefully otherwise plant fragments will resprout into new plants, thus exacerbating the infestation. Both the spines make this a difficult and uncomfortable process). Burning of uprooted plants will help minimise this risk if there is enough dry material to ensure that the material burns. Plants can be treated by herbicide stem injections. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

Controlled burns have been used to control Opuntia species. Such burns must be well-timed and coordinated to reduce the risk of creating a bushfire and there must be sufficient material to carry a hot fire. Fire could be used for small, isolate stands but it will not penetrate large stands.

The moth Cactoblastis cactorum feeds on this plant in its larval stages and can help control Opuntia engelmannii as part of an integrated control programme. It was introduced to Tanzania but never established. It is likely that some cochineal species which feed on Opuntia species have been introduced to East Africa. This group offers some prospects for biological control of Opuntia species.

Legislation

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

References

Anderson, E.F. (2001). The Cactus Family. Timber Press, pp. 497-498.

Turner, R.M., Bowers, J.E. and Burgess, A.L. (1995). Sonoran Desert Plants: an Ecological Atlas. Tucson: The University of Arizona Press, pp. 291-293.

Wikipedia contributors. "Opuntia engelmannii." Wikipedia, The Free Encyclopedia. Accessed March 2011.

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