Game of Thorns
One A.C. MacDonald of the Agriculture Department was engaged in attempts to exterminate the prickly-pear overgrowth near Cookhouse reported Grocott’s Mail on 16 December 1891. MacDonald, who was based in Grahamstown, had hooked up a 900-litre tank of arsenic solution to a wagon, and sprayed a two-acre thicket of prickly pears with it. His goal was to figure out what strength of solution was needed – 1:4, 1:7 or 1:10 – to kill off as many prickly pear plants as possible as cheaply as possible. Arsenic would cause the plant’s leaves to drop off after ten days, but did not seem to affect the woody stem at all.
It also killed everything else it touched. MacDonald thought that the poisoned ground would recover following heavy rain, but this did not make spraying arsenic everywhere any safer. The Grocott’s added that the total cost of MacDonald’s day of experiments was £6, including nearly 50kg of arsenic powder. This was expensive, the newspaper conceded, but necessary: only by experimentation would MacDonald be able to come up with a viable plan to wipe out the highly invasive cactus.
It’s fair to say that by the 1890s, South Africa would have been happy to pay a lot more than £6 to get rid of the prickly pear. Native to Mexico, opuntia ficus-indica had been introduced to many agricultural regions worldwide because of its value as an emergency source of fodder for livestock in arid areas. It could also be used as a boundary marker, as livestock were unwilling to push their way through the spiny leaves, it prevented soil erosion, and also produced delicious fruit. But the cactus, which can grow to 5m in height, did not stay where it was put. Animals spread the seeds when they ate the fruit, and as if that wasn’t enough, entire plants could grow from broken fragments of the leaves.
By the 1920s, the prickly pear infestation was a national disaster in South Africa. Whole stretches of the Eastern Cape were choked with the dense spiny blades, and were no use as grazing land at all. MacDonald’s arsenic solution had eventually proved unsuitable, as a lot of arsenic was needed, and spreading the poison was too dangerous to people, livestock and wildlife.
Salvation eventually came in the form of the cochineal beetle, cactus moth and stem-borer weevil, all of which feasted happily upon the prickly pear, and today the prickly pear population of South Africa is under control. However, it is still classified as a Category 1 weed, which means that it is illegal to plant it. (There is a spineless, edible varietal that is allowed; however, the two plants hybridise easily). Anyone who has driven along the N2 between Port Elizabeth and East London knows how widespread the prickly pear still is, and given the current situation of extreme drought, the question must be asked: should we redouble our efforts to get rid of it as invasive vegetation, or grow more of it to feed animals?
This is the last article in this series. I hope that you have enjoyed reading them as much as I have enjoyed writing them! Queries, suggestions, tips and corrections to firstname.lastname@example.org.