Prickly pear (Opuntia ficus-indica) (Cactaceae)
The weed
Prickly pear (also referred to in South Africa as sweet or mission prickly pear) is of Mexican origin. It is a tree or tall shrub, up to 5 m tall, with a thick, woody trunk. The stems are divided into flattened, narrow, elliptical segments or leafpads (cladodes) that are green but covered with a dull, bluish wax. In the invasive form, the cladodes and trunk are armed with one or more long (up to 2.5 cm), white spines per areole. Furthermore, short, fine bristles (glochids) occur on all the areoles. Prickly pear produces orange flowers that open during the day, and which give rise to elliptical or egg-shaped fruits with colours ranging from yellow and orange to red and purple. Despite numerous glochid-bearing areoles, the fruits have a pale, sweet pulp, which makes them very popular with humans, other mammals and frugivorous birds.
Centuries ago, a hybrid, which had been selected for spinelessness and high fruit quality, was introduced into South Africa, where a variety of cultivars are still being used as a source of fruit and fodder, and as a hedge plant. Subsequently, spiny forms have emerged from these spineless cultivars through cross-pollination. Whereas the spineless cultivars are browsed by various animals, the spiny form is protected from herbivores, thus gaining a competitive advantage that allows them to gradually displace the natural vegetation and pastures. The seeds are dispersed effectively by birds, humans and other mammals. Prickly pear is present throughout the country, but invades mainly dry and rocky places in the savanna, thicket and karoo.
In terms of the Alien and Invasive Species Regulations (AIS), National Environmental Management: Biodiversity Act (Act No 10 of 2004), the spiny form of
O. ficus-indica was declared a category 1 weed, which neccesitates its control, or removal and destruction if possible. No trade or planting of prickly pear is allowed, with the exception of fruit if used for human consumption. However, all spineless cultivars and selections (commonly known as Cactus Pear) are exempt from this legislation, and may be cultivated without legal objections.
Control
Two stem-injected chemicals are registered for use as herbicides against prickly pear in South Africa. However, biological control is a more economical and environmentally-friendly option. Three species of biocontrol agents for prickly pear are present in South Africa. These are a host-specific cochineal species,
cochineal species, Dactylopius opuntiae, the
cactus moth,
Cactoblastis cactorum, and a
stem-boring weevil, Metamasius spinolae. Together, these insects are keeping prickly pear populations at relatively low levels, prevent it from becoming a national disaster again, the way it used to be during the 1920s in the Eastern Cape province. This biological control projects was one of the first such research projects to be undertaken in South Africa.
More information
- A review on the biological control of prickly pear in South Africa was published during 1978
pdf - The following brochures can be downloaded:
- The control (mainly chemical) of prickly pearpdf
- The use of young prickly pear cladodes for human consumptionpdf
- A (biological) control strategy for prickly pearpdf
- A detailed brochure on cochineal insects pdf
- A detailed brochure on the cactus moth pdf
- Two prickly pear stem-boring beetles,
Metamasius spinolae and
Archlagocheirus funestus pdf
Contact: Hildegard Klein, E-mail
KleinH@arc.agric.za
