Opuntia ficus-indica
(prickly pear)

O. ficus-indica is the most widespread and most commercially important cactus, and has been, and continues to be, widely introduced as a commercial fruit and fodder crop and more recently as part of forestry or agroforestry projects in developing countries. This has led to a large improvement to livelihoods, but has also resulted in environmental problems when the plant has become invasive. Animals disperse seed widely and vegetative propagation has made this species difficult to eradicate by mechanical and chemical means. Biological control has proved effective in some areas, but the conflict with commercial production has limited the adoption of this method in other countries.

O. ficus-indica has been cultivated from pre-Columbian times in Mesoamerica and it is thus almost impossible to locate the exact origin of the species, although most ethnobotanists seem to agree that it probably originated in the Central Mexican valley. It has been introduced throughout the world and is very widespread. There is probably hardly a country with Mediterranean or sub-tropical to tropical climate that is without this species, and no attempt has been made to include all records of presence around the world as a cultivated species. The distribution list includes the countries where O. ficus-indica has reverted to spiny forms or where thorny varieties have been introduced, though is likely to be missing many other countries where non-cultivated forms exist, and those where naturalisation has begun to occur.

The risk of further introductions is high, as this species is intentionally planted as a new fruit and fodder crop. It is highly valued as a commercial species and many countries especially in Asia have recently established large-scale plantations. However, historical records appear to indicate a time-lag of about 100 years between introduction and the beginnings of invasive spread, thus the actual risk may be low. It should be noted that Robertson et al. (2003) ranked O. ficus-indica as the third most important invasive plant in terms of management requirements in South Africa.

It is native to regions with a temperate to sub-tropical climate with typical summer rains and cool and dry winters (Hoffmann, 1995). In other parts of the world where O. ficus-indica is invasive, similar climates exist, for example in Eritrea, Ethiopia and the Eastern Cape, South Africa. Although it is now successfully cultivated in several Mediterranean countries, critical moisture shortage can be a limiting factor during the hot and dry summers unless the plantations are irrigated, which may explain why the plant has never seriously invaded Mediterranean areas. Its climatic tolerances are wide and it can proliferate in rainfall regimes of 250 to 1200 mm per annum with very hot summers of over 40°C, and cold winters with temperatures frequently falling below 0°C for brief durations (Le Houérou, 2002). Plants do not tolerate salinity but thrive on well-drained soils and because of their superficially spreading root system can proliferate in shallow and rocky substrates. Abandoned agricultural land is ideal for O. ficus-indica invasion, and it also establishes well in disturbed savanna, bush and shrub land vegetation but poorly in high rainfall grassland. Around the Mediterranean, from Spain to Turkey (Bekir, 2006), it can often be found growing on pathsides or roadsides, on sleep slopes and rocky outcrops where little else grow, as well as around fields and suburban plots, and here, thickets can be dense, and may reach many metres in height. O. ficus-indica does not thrive in tropical situations with constantly high humidities, in shady conditions, nor in areas with extreme drought or very long dry periods.

O. ficus-indica is not a normally a crop weed. However, in Ethiopia, infestations and hedges that surround cultivated lands are invading from the periphery, which then gradually reduce the cultivatable area and farmers have very limited means to control these invading plants from their lands. These aggressive invasions can, in time, take over entire cultivated land areas. Dense infestations also out-compete with other plants eventually leading to monospecific stands of O. ficus-indica which occurs on pastures and grazing is severely impeded, with stock forced to eat predominantly O. ficus-indica for survival.

Genetics

The genetic history of many domesticated plants is difficult to unravel and O. ficus-indica is no exception. This and many similar species in Mexico show great phenotypic variability, especially in rural home gardens where man has been cross-breeding and selecting types for his specific needs. This variability of domesticated and wild populations arose via natural hybridization and selection associated with polyploidy and geographic isolation (Gibson and Nobel, 1986). These varieties further reproduced by self-fertilization, fraternal crossing with sister plants or the original parent giving rise to further variation (Grant and Grant, 1979). During the early stages of domestication, phenotypes with higher ploidy levels, vigorous cladodes and bigger fruit were probably preferentially selected and established in gardens and small cultivations (Pimienta-Barrios and Munoz-Urias, 1995). It is these selections were probably introduced to Europe and later elsewhere. Cultivated O. ficus-indica plants are all octoploids with 2n=88 chromosomes according to Pimienta-Barrios and Munoz-Urias (1995), whereas Nobel (2002) notes that cultivated forms may be octoploids (2n=88) or hexaploids (2n=66). Spontaneous forms are either diploid (2n=22) or tetraploid (2n=44) (Nobel, 2002).

Phenology and Physiology

The ecological successes of O. ficus-indica and other Opuntiae lies mainly in their ability to conserve water. This is done by means of the CAM (Crassulacean acid metabolism) photosynthetic pathway which conserves water by nocturnal stomatal opening and by a relatively small stomatal surface area (Nobel, 1995; Nobel and Bobich, 2002) while still retaining a high productivity compared to other plants (Nobel, 1988; 1994). In addition O. ficus-indica is able to store water within their vacuoles in the photosynthetic and parenchyma cells. Further adaptations include the epidermis, a single layer of cells on the outer side of the chlorenchyma and the thick, waxy, waterproof cuticle. Germination and the survival of the young seedling are the critical phases in the phenology of O. ficus-indica. Survival is higher where seedlings are associated with nurse plants for protection. Once the seedlings have reached the 4-cladode stage and have become succulent, survival is considerably increased. Plants originating from seeds take longer to establish and flower than plants from cuttings.

Among the main modifications in the course of evolution of Opuntia are the modified stems (cladodes) which have undergone changes towards succulency including increased stomatal frequency, a palisade cortex, a large internal surface area due to extensive intercellular spaces, wood modifications and atypical pith features (Sudzuki Hills, 1995). Very young cladodes produce rudimentary leaves which dehisce within about a week leaving the plant leafless with the cladodes becoming increasingly succulent and taking over the function of leaves. A typical feature of the younger cladodes are the areoles which are the axillary buds imbedded in the epidermis and which give rise to new shoots, flowers and roots from the meristematic tissue. They are distributed over the entire surface of a cladode in a helical pattern. Spines also develop from the basal meristem cells in the areoles and could be either the typical long white ones or the very short ones that occur as clusters inside the cavities of the areoles and are known as glochids (spine hairs). Older cladodes become more woody and the green epidermis is eventually replaced by bark (periderm). These woody stems provide the necessary support that eventually gives rise to the typical shape of an O. ficus-indica tree. O. ficus-indica has a life-span of over 80 years.

Reproductive Biology

Reproduction is both sexual and vegetative (Pimiento-Barrios and Del Castillo, 2002). Even a small section of a cladode can root and grow provided there are at least two areoles present. Pieces of a cladode can survive for long periods in extreme conditions waiting for moisture to take root. Asexual reproduction can also be apomyctic when embryogenesis occurs without pollination, and in O. ficus-indica, 10.9 to 18.5% of the seeds are produced by apomyxis (Mondragon-Jacobo and Pimiento-Barrios, 1995). The number of viable seeds per fruit can vary from 177 to 357 with a few aborted seeds present. Although scarification is necessary for germination, the dormancy period is short and maximum germination occurs after 9 months where seeds have been stored at room temperature.

Environmental Requirements

O. ficus-indica colonizes well in areas with mild winters usually associated with a prolonged dry spell followed by a hot summer rainfall period of low humidity. This explains in part why O. ficus-indica is less invasive in Mediterranean climates although it has become an important crop in these areas. A mean annual rainfall of 350–500 mm is required for good growth (Inglese, 1995). O. ficus-indica is well adapted to proliferate in a wide range of soils, from sub-acid to sub-alkaline provided the clay content does not exceed 15–20% and the soil is well-drained. The superficial root system allows the plant to grow in shallow soils and explains why O. ficus-indica proliferates on mountain slopes.

O. ficus-indica is not invasive in its country of origin, Mexico, for several reasons. Firstly, the plant is heavily utilized by man and animals and secondly, the plant is under constant attack by a large complex of specialized natural enemies and diseases (Zimmermann and Granata, 2002). In the countries of introduction, O. ficus-indica is released from this pressure and this explains in part its aggressive behaviour in these areas. Although some polyphagous insects may occasionally feed on O. ficus-indica in introduced countries, this is sporadic and of no consequence.

Animal feed, fodder, forage

• Forage
• Invertebrate food for dye-containing insects

Environmental

• Agroforestry
• Erosion control or dune stabilization
• Revegetation
• Shade and shelter
• Soil conservation
• Windbreak

Human food and beverage

• Emergency (famine) food
• Fruits
• Honey/honey flora
• Seeds
• Vegetable

Materials

• Dye/tanning

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Ornamental

• Christmas tree
• Cut flower
• garden plant
• Potted plant
• Propagation material
• Seed trade

O. ficus-indica is often confused with several other similar tree-like Opuntia species including Opuntia megacantha, Opuntia streptacantha, Opuntia tomentosa and Opuntia amyclaea, the former also included as synonyms in this datasheet. The confusion is compounded by the many varieties or cultivars that have been selected over the course of several thousand years (Kiesling, 1999). The lack of thorns is a defining character where this feature is retained, but separation of thorny types may be difficult.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Cultural control

One of the novel methods of dealing with the problem of O. ficus-indica invasion in countries such as Ethiopia is to treat it not as a weed but as an abundant resource – control by utilization. People are exposed through extension programmes to all the uses of the plant with emphasis on fodder, 'nopalitos' (cladodes, or leaf pads) for human consumption, and production of cochineal dye, and by doing so, reduce the O. ficus-indica populations (Haile et al., 2002). However, for adequate control, utilization may need to be combined with chemical and mechanical methods in certain areas as utilization alone may not reduce large infestations. By providing inhabitants with new sources of income it is hoped that better tools and equipment can be purchased to help manage and process this resource more effectively. Harvesting the fruit can provide additional nutrition especially in terms of vitamin C, possible financial gains if sold, and will also reduce propagule pressure. However, in a control programme, it is likely that better management may depend more on utilisation of the leaves (cladodes) as a fodder source, as these comprise the vast bulk of the standing biomass, are also propagules, and can provide large volumes of fodder often where alternative sources are lacking. Thornless cladodes are made more palatable by ‘wilting’, i.e. curing and leaving them to dry out for a number of days or weeks before allowing livestock to feed on them. In the Americas, wild native thorny Opuntia can be made palatable by singeing or burning off the spines; in Texas, USA this being carried out in the dry season with a flame-thrower. Cattle there are habituated, and when hungry and thirsty, will run in from far away at the sound of the flame-thrower in operation.

Mechanical control

Grubbing, cutting and removing O. ficus-indica as a control method is highly labour intensive and may aggrevate the infestations because it results in many new 'cuttings' which take root and develop into new plants. This is, however, the predominant method employed in Tigray, in the lowlands of Ethiopia where O. ficus-indica invades cultivated lands, as Ethiopian farmers have very limited means to control the species although this does allow them to maximise the use of the plant as a fodder resource. Prior to biological control in South Africa, O. ficus-indica plants were cut in pieces, stacked and burnt. The shortage of fuel to burn O. ficus-indica excludes this method from other problem areas such as Ethiopia and Somalia.

Chemical control

Arsenic-based herbicides are very effective against all members of the Cactaceae. In the past, arsenic pentoxide was widely and successfully used in many countries. When use of this herbicide became unacceptable, hormone-based herbicides were used, e.g. picloram (Pritchard, 1993). The method prescribed in South Africa required plants to be cut and piled into a heap before treatment. This method proved to be very expensive, and Australia and South Africa embarked on a subsidy scheme to assist landowners in controlling O. ficus-indica. The herbicide MSMA, an organic arsenate with relatively low toxicity, was later registered for O. ficus-indica control in South Africa. Treatment is by means of stem injection of equal parts of MSMA and water thus reducing the need for the use of large volumes of herbicides (Zimmermann, 1989).

Biological control

Several countries opted for biological control after conventional control was shown to be ineffective (Julien and Griffiths, 1998). Other countries do not consider biological control as a solution because a large proportion of the population also depends on the plant as a source of food and fodder. However, in other parts of these same countries, O. ficus-indica is also regarded as a pest and threat and this conflict of interest limits the control methods available.

Hawaii, Australia and South Africa have used biological control to reduce O. ficus-indica infestations along with other Opuntia species. Control was achieved using mainly four insects introduced from Argentina, Mexico and the USA, namely, the cactus moth, Cactoblastis cactorum, the cochineal Dactylopius opuntia, the long-horn stem borer, Archlagocheirus funestus and the stem-boring weevil, Metamasius (Cactophagus) spinolae (Dodd, 1940; Pettey, 1948; Mann, 1970; Annecke and Moran, 1978; Moran and Zimmermann, 1984). The control achieved was satisfactory, with the cochineal D. opuntiae achieving best results in South Africa where infested plants are felled and stacked. The cactus moth C. cactorum was not able to kill large plants but is an excellent biological control agent of smaller plants with less than 10 cladodes (Zimmermann and Malan, 1981). The cactus weevil, M. spinolae, released in South Africa in 1948, gives total control of large plants but dispersal is very slow from the point of release (Zimmermann and Moran, 1991). Overall, the biological control of O. ficus-indica in South Africa was satisfactory to the point where the remaining populations are not a threat and are now being utilized fully with no risk of continued invasions. Although both C. cactorum and D. opuntiae are now pests in commercial cactus pear plantations, they can be easily controlled and do not prevent the commercial production of fruit and fodder. In retrospect, the decision to opt for biological control in South Africa, and knowing well the consequences for commercial cactus pear production, was still a good one as several important Opuntia invaders, including O. ficus-indica, are kept under control by these two natural enemies (Annecke and Moran, 1978). Other countries such as Ethiopia, where circumstances are different, have decided not to use biological control and instead opted to embark on a campaign to increase the utilization of the resource as a control method.

Integrated control

In South Africa, the integration of biological and chemical control is the best option for some landowners who decide to, or are obliged to, remove or reduce O. ficus-indica infestations on their land. During some years, usually in association with wet cycles, there is a resurgence of O. ficus-indica and landowners become concerned that the situation that prevailed before biological control may return. Populations of the cactus moth C. cactorum usually increase where there is an abundance of small plants and good control is usually achieved within a few years, assisted by the cochineal D. opuntiae during hot and dry seasons. Landowners limit chemical control using stem-injections of MSMA for plants larger than the 14-cladode stage as these may not succumb to attack by the cactus moth. This integration of control methods can also be combined with utilizing O. ficus-indica as a fodder resource. Special equipment is employed, which shreds O. ficus-indica plant material, which is then mixed with other fodder and fed to cattle and sheep.

27/11/2007 Updated by:

Nick Pasiecznik, Consultant, France