|Weeds in our Area (Part Ninety Six)
By Bob and Ena McIntyre – Garden Route
Succulents enjoy great popularity and the indigenous South African succulents of Namaqualand, the Little Karoo and Namibia are world famous and equalled in number only by those of the Americas, which includes their cacti - the origin of the local invasive populations. Cacti interestingly are sophisticated succulents with amazing adaptations for survival in hostile, arid environments. Many of these plants are imposing in appearance no doubt adding to their appeal as ornamentals. South African climatic conditions are generally conducive to growing them very successfully. The fruit of some make excellent eating, and the foliage is good animal fodder, and the plants were useful for security hedging. As things happen, we seldom keep a close enough watch and invasions of these plants have reached nightmare proportions throughout our country.
In Article 19 of September 2004 we very briefly touched on these nasties. Since then we’ve been keeping a close watch on the species. Walking along Whites Rd, driving along the N2 to the east of Wilderness village and taking a trip over the mountain into the Oudtshoorn area - one just has to notice how these undesirables are proliferating. In the locations mentioned above we have identified four different types of cactus – Whites Rd: Sweet prickly pear (Opuntia ficus-indica) (illustrated), Cochineal or drooping prickly pear (Opuntia monocantha), along the N2: Moon cactus (Harrisia martinii) (illustrated), Oudtshoorn district: Sweet prickly pear and the torch cactus (Echinopsis spachiana) (illustrated) and then of course in many gardens we still have the “ornamental” queen of the night (Cereus jamacaru) (illustrated). All the above are Category One declared weeds and should be destroyed (except for the spineless cultivars of Opuntia ficus-indica).
Identification: The plants are characterised by succulent stems (cladodes) covered with nasty spines. Some have miniscule leaves that drop off very quickly and several have no leaves at all. The flowers are invariably very attractive but short-lived. Some plants have distinctive shapes – the moon cactus is a spiny succulent shrub with a multitude of long arching stems, the torch cactus has a fat clump of furry grey-green stems that grow up to 1.5m tall, the cochineal cactus has bright green, flattened stems and a wilted appearance.
Control: Some Cactus species have been very effectively controlled with variants of the Cochineal bug, originally introduced in the 1930’s. This method is however only really effective for very dense stands of the invader. Isolated plants should be sprayed or injected with a registered herbicide, e.g. MSMA 720 SL or a glyphosate. Manual control by way of uprooting, desiccating and burning is another option. The plants regrow readily from pieces broken off - please take care that all unwanted material is disposed of responsibly.
References: Alien Weeds and Invasive Plants by Lesley Henderson, Copyright © 2001 Agricultural Research Council, A-Z of Gardening in SA, W. Sheat.