Click on images to enlarge
stem segment damaged by biocontrol agents (Photo: Sheldon Navie)
young stem segment with tiny leaves (Photo: Sheldon Navie)
flower and flower buds (Photo: Sheldon Navie)
stem segments (Photo: Sheldon Navie)
habit (Photo: Sheldon Navie)
seedlings (Photo: Sheldon Navie)
habit of same plant following attack by biocontrol agents (Photo: Sheldon Navie)
close-up of flower (Photo: Sheldon Navie)
close-up of stem segment (Photo: Sheldon Navie)
infestation (Photo: Sheldon Navie)
Opuntia stricta (Haw.) Haw.
Opuntia dillenni (Ker Gawl) Haw.; Cactus strictus Haw.; Opuntia stricta (Haw.) Haw. var. stricta; Opuntia airampo Phil.; Opuntia anahuacensis Griffiths; Opuntia zebrinaSmall
Common prickly pear, Australian pest pear, coastal prickly pear, common pest pear, common prickly pear, erect prickly pear, pest prickly pear, prickly pear, sour prickly pear, southern spineless cactus
Native to the Caribbean region.
Locations within which Opuntia stricta is naturalised include Australia, east and south Asia, the Middle East, Spain, northern, southern and eastern Africa.
Opuntia stricta is invasive in parts of Kenya (A.B.R. Witt pers. obs.) and is present in Uganda and Tanzania. It is common in northern Kenya (Laikipia and in the north-east) and Tsavo East National Park - east of Voi (A.B.R. Witt pers. comm.). The species was introduced to East Africa in the 1950s. In Kenya, the species has become increasingly problematic in recent years with deterioration in rangeland, creating a perfect opportunity for invasion by O. stricta.
A common weed of semi-arid, subtropical, tropical and warmer temperate regions. It inhabits open woodlands, rangelands, grasslands, pastures, riparian zones (banks of water courses), roadsides, railways lines, coastal environs, gardens, disturbed sites and waste areas. The species is known to invade rocky slopes and river banks as well as degraded area in grasslands and woodlands.
The stems are much-branched and consist of a series of flattened, fleshy (succulent), segments (cladodes). The cladodes (10-35 cm long, 7-20 cm wide, and 10-20 mm thick) are green or bluish-green in colour and longer than they are broad (obovate in shape). They are hairless (glabrous) and covered in small raised structures (areoles) which bear tiny spiny bristles (glochids). The areoles either do not have any spines or may have one or two long sharp spines (2-4 cm long).
The flowers (up to 7 cm long and 6-8 cm across) are bright yellow, but often have pinkish or reddish coloured markings on the outer 'petals'' (most of these are actually petal-like structures known as petaloids). They are borne singly on fleshy bases along the margins of the cladodes. Each flower has large numbers of petaloids and numerous stamens.
The immature fruit are green in colour, but they turn reddish-purple as they mature. These berries (4-8 cm long and 2.5-4 cm wide) are fleshy (succulent), egg-shaped (obovoid), and usually have slightly depressed tips. Each fruit has several tufts of glochids on its surface. The reddish or purplish coloured pulp in the centre of the fruit contains large numbers of seeds. These seeds (4-5 mm long and 4-4.5 mm wide) are generally yellow or pale brown in colour and somewhat rounded (sub-globular) in shape.
This plant reproduces by seed and also vegetatively via its fleshy cladodes which become dislodged from the plant and produce roots. Cladodes are spread by becoming attached to animals, footwear and vehicles. They may also be dispersed by floodwaters and in dumped garden waste. The fruit are eaten by various animals (e.g. birds and rodents) and the seeds then spread in their droppings.
Opuntia stricta is used as a barrier fence and in some parts of the world as livestock fodder.
Opuntia stricta is a very serious problem in the arid lands. It is an irritant due to its spines and glochids (barbed hairs or bristles). People have abandoned homes/villages as a result of this weed. It prevents access, displaces native species and causes injuries to people, livestock and to wild animals. Pastoralists claim that excessive consumption of fruit by livestock causes death - some pastoralists reckon they have lost all of their livestock.
O. stricta is regarded as an environmental weed in many parts of the world. It has been nominated as among 100 of the "World's Worst" invaders by the IUCN Invasive Species Specialist Group and it has been listed as a noxious weed in South Africa and in most Australian states.
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 monacantha 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.
Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.
Germplasm Resources Information Network (GRIN). www.ars-grin.gov/npgs/index.html. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA. Accessed March 2011.
Global Compendium of Weeds. www.hear.org/gcw. Hawaiian Ecosystems at Risk Project. Accessed March 2011.
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.
Lazarides, M., Cowley, K. and Hohnen, P. (1997). CSIRO Handbook of Australian Weeds. CSIRO Publishing, Collingwood, Victoria.
Pacific Island Ecosystems at Risk (PIER). Opuntia stricta (Haw.) Haw., Cactaceae: plant threats to Pacific ecosystems. www.hear.org/pier/species/opuntia_stricta.htm. Institute of Pacific Islands Forestry, Hawaii, USA.
Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.
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).
BioNET-EAFRINET Regional Coordinator: [email protected]