Prickly Pears: Invaders?

Prickly Pear (Opuntia ficus-indica)

Prickly Pear, when approaching the subject from the alien invader control side, poses a prickly situation. Is it a weed or not? After some research, I have found out that there is a cultivated plant and an invader.

The Prickly Pear can be found spread throughout the country, it favours dry rocky places like the Magaliesberg and the Karoo. The plant spreads via seeds in animal droppings. Birds and baboons eat the spineless variant as well as the fruit from the spined variant. It is important to note that through cross-pollination the plant can revert back to its spiny invader form.

Originally from Mexico, a spineless hybrid of the plant was introduced into South Africa as animal fodder. The shrub can grow up to 5m tall. It grows upright with its stem forming leafless cladodes between 20 and 60cm long. The invasive version is covered in spines up to 2.5cm long while the cultivated version lacks spines. Each areole, on the invasive species, will have 1 or more spines. Prickly Pears have orange flowers that open during the day and produce fruit with sweet, edible pulp. As the invader variant is guarded by spines, it is more likely to survive and spread. It will slowly overwhelm natural vegetation, hence its classification as a category 1 weed.

Prickly Pear has become a popular crop due to the times of drought South Africa has been through recently. The cultivated version is referred to as “sweet” Prickly Pear. This variant of the plant has no spines; they flower between October and December and produce edible “egg-shaped” fruit. The rest of the plant is also edible as a vegetable (this is quite common in Mexico, where the pads are called “Nopals”). I recently tried this out using the invasive variant as I must remove them anyway. Braaing the pads and adding it to our potato salad worked out rather nicely. They produce quite a lot of “gooey” liquid when being cooked. I’ll add some photos of the process at the end of the post.

Controlling the invasive variant can prove difficult if they are left to form thickets of the plant. I found this video rather interesting: https://www.youtube.com/watch?v=K9THmDhhA4A. The video speaks about an infestation of Prickly Pear in the Karoo in the early 1900’s. There are several ways to control the plant depending on how bad the infestation is and the size of the plants you need to remove. Removal and bio-control options are possible. 

Removal Method: Smaller plants can be pulled out by the root and crushed (They can create quite a splash!). For larger plants, you will need to remove the root; this can be done by cutting it to ground level (below the spines) and pulling or kicking it out. The whole plant should then be put up in a tree or on a rock in the sun to dry out. Placing the plant in the sun is vital, otherwise it will regenerate from the cladode if in contact with the soil.

Bio-control Method: Dactylopius opuntiae are a cochineal insect (insects that only feed on plants of the cactus species). When introduced to the Prickly Pear population, it causes yellowing of the leaves (Cladodes) and will eventually cause the plants to die. However, this method is not effective on young plants in the shade.

Another method of bio-control is the Cactus Moth (Cactoblastis cactorum). The moth lays eggs, that imitate a spine, on the cladodes. When the larvae hatch, they will hollow out the cladodes of larger plants causing rot and eventually the death of the plant.

Further reading and references:

https://www.farmersweekly.co.za/agri-technology/farming-for-tomorrow/commercial-potential-for-the-humble-cactus-pear/

https://www.arc.agric.za/arc-ppri/Pages/Prickly-pear.aspx

“A Field Guide to the Invasive Alien Plants of the Magaliesberg”, (Klein & Neser)

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