Opuntia ficus-indica
(prickly pear)

Pictures

Picture	Title	Caption	Copyright
Title Flower and young fruit Caption Opuntia ficus-indica (prickly pear); cladode with flower and young fruit. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Flower and young fruit	Opuntia ficus-indica (prickly pear); cladode with flower and young fruit.	©Plant Protection Research Institute, Pretoria, South Africa
Title Habit Caption Opuntia ficus-indica (prickly pear); dense infestation in Tigray, northern Ethiopia. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Habit	Opuntia ficus-indica (prickly pear); dense infestation in Tigray, northern Ethiopia.	©Plant Protection Research Institute, Pretoria, South Africa
Title Natural enemy Caption Opuntia ficus-indica (prickly pear); Dactylopius opuntiae infesting a cladode. It is a highly effective biological control agent. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Natural enemy	Opuntia ficus-indica (prickly pear); Dactylopius opuntiae infesting a cladode. It is a highly effective biological control agent.	©Plant Protection Research Institute, Pretoria, South Africa
Title Larvae attacking prickly pear|Natural enemy Caption Opuntia ficus-indica (prickly pear); Cactoblastis cactorum larvae infesting a prickly pear cladode. This natural enemy is effective in controlling small plants. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Larvae attacking prickly pear|Natural enemy	Opuntia ficus-indica (prickly pear); Cactoblastis cactorum larvae infesting a prickly pear cladode. This natural enemy is effective in controlling small plants.	©Plant Protection Research Institute, Pretoria, South Africa
Title Natural enemy Caption Opuntia ficus-indica (prickly pear); larvae of the natural enemy, Cactoblastis cactorum (cactus moth). Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Natural enemy	Opuntia ficus-indica (prickly pear); larvae of the natural enemy, Cactoblastis cactorum (cactus moth).	©Plant Protection Research Institute, Pretoria, South Africa
Title Harvested fruits Caption Opuntia ficus-indica (prickly pear); fruit harvest from infestations to be sold on the informal market. South Africa. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Harvested fruits	Opuntia ficus-indica (prickly pear); fruit harvest from infestations to be sold on the informal market. South Africa.	©Plant Protection Research Institute, Pretoria, South Africa
Title Fruits for sale Caption Opuntia ficus-indica (prickly pear); roadside vendors selling prickly pear fruit harvested from infestations. South Africa. Copyright ©Plant Protection Research Institute, Pretoria, South Africa	Fruits for sale	Opuntia ficus-indica (prickly pear); roadside vendors selling prickly pear fruit harvested from infestations. South Africa.	©Plant Protection Research Institute, Pretoria, South Africa

Identity

Preferred Scientific Name

• Opuntia ficus-indica (L.) Mill.

Preferred Common Name

• prickly pear

Other Scientific Names

• Cactus compressus Salisb.
• Cactus ficus-indica L.
• Cactus opuntia L.
• Opuntia compressa McBride
• Opuntia cordobensis Speg.
• Opuntia ficus-barbarica Berger
• Opuntia gymnocarpa F.A.C. Weber
• Opuntia megacantha Salm-Dyck
• Opuntia streptacantha Lem.
• Opuntia tuna-blanca Speg.
• Opuntia vulgaris Mill.

International Common Names

• English: barbary fig; cactus pear; Indian fig; Indian fig prickly pear; Indian pricklypear; mission fig; smooth prickly pear
• Spanish: chumba; chumbera; higo Indico; higuera de las Indias; nopal de castille; tuna; tuna mansa
• French: figuier de barbarie; figuier d'Inde

Local Common Names

• Brazil: nopal; palma adensada; palma forrageira; palma-de-gado
• Ethiopia: beles
• France: raquette
• Germany: Indischer Feigenkaktus
• Italy: fico d'India; pero pungente
• Mexico: nochtli
• Netherlands: schijfcactus
• South Africa: turksvy

EPPO code

• OPUFI (Opuntia ficus-indica)

Summary of Invasiveness

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 lead 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.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Caryophyllales
•                         Family: Cactaceae
•                             Genus: Opuntia
•                                 Species: Opuntia ficus-indica

Notes on Taxonomy and Nomenclature

Considerable variation within many Opuntia species is common. The taxonomic confusion started when taxonomists described new species from single specimens resulting in names being created for variants or biotypes within a species. This problem is particularly apparent in Opuntia and DNA sequencing is now being applied to resolve the confusion. Many species are now recognized as mere variants of O. ficus-indica. Kiesling (1999) recognized two forms of O. ficus-indica, namely, O. ficus-indica f. ficus-indica (including O. tuna-blanca Speg., O. ficus-indica var. gymnocarpa Speg., O. ficus-indica var. decumana (Willd.) Speg.) and O. ficus-indica f. amyclaea (Ten.) Schelle (including O. cordobensis Speg., O. megacantha Salm-Dick and O. streptacatha Lem.). However, although it was suggested by Kielsling (1999) that O. megacantha and O. streptacatha be retained, they are treated as synonyms within this datasheet. Other names that were used for this species include Cactus ficus-indica L., C. opuntia L., Opuntia vulgaris P. Miller (including Platyopuntia vulgaris (P. Miller) F. Ritter), C. compressus R. A. Salisbury, O. compressa McBride and O. ficus-barbarica Berger (Anderson, 2001). Recently, Scheinvar (1995) described a new species, O. albicarpa Scheinvar which groups together O. megacantha, O. amyclaea and O. ficus-indica var. amyclaea so adding to the taxonomic confusion surrounding the O. ficus-indica taxon. Concerning common names, 'prickly pear' is now more widely used to describe the spiny, wild-growing and weedy types of O. ficus-indica whereas 'cactus pear' is confined to the spineless forms which are widely cultivated. Many other names are also commonly used (e.g. Bravo-Hollis, 1978).

Description

O. ficus-indica is a large trunk-forming segmented cactus which can attain a height of 5-7 m with a crown of over 3 m in diameter and a trunk up to 1 m in diameter. Cladodes are green to blue-green, whereas the terminal cladodes are always bright green and produce the flowers and new growth. Large pads (cladodes) bear few spines to 2.5 cm or are completely spineless. Cladodes are obovate to oblong, 20-60 cm long and 10-40 cm wide, generally a half to two-thirds as broad as long. Glochids are yellow, numerous, caducous, or may not be present. Basal cladodes become woody with age. Flowers form on the perimeter of the cladodes, yellow or orange, cup-shaped, 6-7 cm long by 5-7 cm across. The fruit is oblong, 5-10 cm long by 4-9 cm across, green at first ripening to yellow, orange, red or purple in colour depending on the variety.

Plant Type

Distribution

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.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

Probably originating from the central Mexican plateau, O. ficus-indica has been introduced to all continents except Antarctica, following the colonization of the Americas. The first introductions to Europe in the 1500s were more as a curiosity, and the multiple uses of the plant were only discovered later. Spineless forms of cactus pear are used in cultivation because they are always vegetatively reproduced whereas the main means of the spread of the spiny weedy O. ficus-indica is by seeds (Annecke and Moran, 1978). It is speculated that mainly spineless types were initially cultivated and that, as the plants naturalized and spread, they reverted back to the original spiny and weedy forms through gene recombination and natural selection, as animals would avoid feeding on spiny types preferring the spineless ones.

Infestations of the spiny O. ficus-indica are recorded from countries that have cultivated it for more than 100 years and it is very invasive in Australia, Eritrea, Ethiopia, South Africa and Hawaii, USA and also to some extent in Somalia and Yemen (Brutsch and Zimmermann, 1995). Countries that have only recently started to cultivate O. ficus-indica, e.g. Brazil, China, India and Pakistan are likely to see similar developments occurring, although the process may take up to 100 years. Infestations do not develop easily in strictly Mediterranean climates because of the long and dry summers. However, Le Houérou (2002) notes that cactus plantations and hedges probably cover approximately one million hectares in the Mediterraean Basin, including O. ficus-indica fa. amyclaea (the spiny form), but unlike in other subtropical zones, cacti never became an invasive pest. Le Houérou (2002) concludes that spineless cacti never become invasive pests as they are grazed out, unless totally protected from herbivores, either naturally (cliffs) or artificially (fences).

Risk of Introduction

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.

Habitat

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.

Habitat List

Hosts/Species Affected

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.

Biology and Ecology

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.

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Rainfall Regime

Soil Tolerances

Soil drainage

• free

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• light
• medium

Special soil tolerances

• shallow

Natural enemies

Notes on Natural Enemies

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.

Means of Movement and Dispersal

Natural Dispersal (Non-Biotic)

Non-biotic natural dispersal does not play a major role in the spread of O. ficus-indica. However, some seeds may be transported by floods to lower-lying areas, but this is thought to be a minimal route of dispersal. Also, cladodes that fall to the ground, often during the fruiting season, root and grow and this causes local increases in stand density and minor local spread.

Vector Transmission (Biotic)

Most dispersal is via many animals, including antelopes, baboons, monkeys, elephants and birds, but also man, which all eat the fruit and disperse the seeds.

Intentional Introduction

Man is by far the most important long-distance vector of O. ficus-indica. Since the colonization of the New World, all introductions can be traced to deliberate planting by missionaries, colonists and more recently development agencies (Bright, 1998). Plants were then carried by landowners to the most remote parts of the countries of introduction. The same qualities that make an agroforestry species successful are often the same ones leading to invasion (Hughes, 1995). The resulting conflicts of interest restrict control options and in such cases biological control is seldom an acceptable solution. Methods to deal with such complicated cases are available, provided the problem is recognized at an early stage of invasion (Hughes, 1995; Zimmermann and Olckers, 2003).

Pathway Causes

Pathway Vectors

Plant Trade

Impact Summary

Impact

O. ficus-indica reduces the availability of pasture grasses and invades crop land in some countries, though the actual economic loses have not been quantified. Also, where livestock are forced to feed almost exclusively on O. ficus-indica this can lead to a loss of condition or even result in death. However, O. ficus-indica is regarded as both an aggressive invader and as a source of food in the areas where the plant proliferates. That O. ficus-indica is a commercial crop will mean that there are often substantial economic gains from presence of this species leading to a requirement for balancing economic calculations to evaluate whether there are gains or losses in any given situation. This conflict of interest also restricts the control options available. The more O. ficus-indica invades an area the more people become dependent on it because it will also reduce the availability of other options or resources.

Economic Impact

O. ficus-indica reduces the availability of pasture grasses and invades crop land in some countries, though the actual economic loses have not been quantified. Also, where livestock are forced to feed almost exclusively on O. ficus-indica this can lead to a loss of condition or even result in death. However, O. ficus-indica is regarded as both an aggressive invader and as a source of food in the areas where the plant proliferates. That O. ficus-indica is a commercial crop will mean that there are often substantial economic gains from presence of this species leading to a requirement for balancing economic calculations to evaluate whether there are gains or losses in any given situation. This conflict of interest also restricts the control options available. The more O. ficus-indica invades an area the more people become dependent on it because it will also reduce the availability of other options or resources.

A detailed study on the positive versus negative impacts of O. ficus-indica on rural livelihoods was recently carried out in South Africa (Shackleton et al., 2007). This found that in areas where invasion was widespread, local people did not want it controlled, rather the inverse, that they wanted more of it. At one site, “92% of people wanted prickly pear at the highest possible densities. Reasons for this included: (1) they loved it and wanted more, (2) such densities would provide enough fruit for more people to sell, (3) it would reduce the distance required to walk to find sufficient quantities, (4) it was “beautiful to look at,” and (5) it was a useful supplementary food.” On the basis of this study, it would appear essential to assessment the views of local people before considering the implementation of any control programme, and O. ficus-indica is clearly a highly valued species.

Environmental Impact

O. ficus-indica has the ability to out-compete all other vegetation. The invasion process is exacerbated by selective grazing of stock on the few remaining native plants which eventually results in monocultures of O. ficus-indica with a dramatic loss of biodiversity.

Threatened Species

Social Impact

Where people have to abandon their land because of invasions, the social impact can be severe. The abundance of fruit for a short period of the year also creates health problems, mainly malnutrition and constipation. As the process of invasion is slow, sometimes spanning two or more human generations, people's perception also change with time to the extent that invasions are regarded as natural or normal. Even more so, Shackleton et al. (2007) found that villagers in parts of South Africa found that invasion had had a very positive effect upon them, leading to improved livelihoods, and they would prefer a higher plant density in most places.

Risk and Impact Factors

• Proved invasive outside its native range
• Abundant in its native range
• Highly adaptable to different environments
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Highly mobile locally
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually
• Has high genetic variability

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Negatively impacts agriculture
• Negatively impacts tourism
• Reduced amenity values
• Reduced native biodiversity
• Transportation disruption

• Competition - monopolizing resources
• Competition - shading
• Competition
• Interaction with other invasive species
• Rapid growth
• Produces spines, thorns or burrs

• Highly likely to be transported internationally deliberately
• Difficult/costly to control

Uses

Both the spiny as well as the spineless varieties of O. ficus-indica are extensively used as a source of food, fodder and for producing dyes. The fruits are widely commercialized in many parts of the world, eaten raw, and have one of the highest concentrations of vitamin C of any fruit. Figures are not available for the global commercial trade in O. ficus-indica fruit as much is very localised other large international export markets exist. In addition, in parts of the Americas, the leaves (or cladodes) are traded, being cooked and eaten as a vegetable known as 'nopalitos'. Cochineal insects are reared and multiplied on O. ficus-indica plants to be processed for the dye (carminic acid) they contain; and there are also numerous other secondary products (Saenz-Hernandez, 1995), including medicinal uses (Andrade et al., 2006) and an oil from the seeds. Thornless forms provide an excellent supplementary livestock forage, thorny forms also if these are burned off prior to feeding, and special fodder varieties are extensively planted, often in rows, in and around fiends and pastures for this purpose. Integrated agroforestry systems including rows of Opuntia with rows of forage legumes are used in some regions, such as the semi-arid North-East of Brazil. Commercial production is most developed in Mexico where indigenous people have learned to utilize this resource over thousands of years. Although O. ficus-indica makes a good fodder, animals need supplementary feeds to make up for deficiencies in a pure cactus diet, and also, the high water content causes severe diarrhoea in animals if left to feed on O. ficus-indica for too long (Mondragon-Jacobo and Perez-Gonzalez, 2001).

Uses List

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

General

• Ornamental

Human food and beverage

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

Materials

• Dye/tanning

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Ornamental

• Potted plant

Similarities to Other Species/Conditions

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.

Prevention and Control

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.

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Contributors

27/11/2007 Updated by:

Nick Pasiecznik, Consultant, France

Distribution Maps