|Weeds in our Area (Part Seventy Four)
By Bob and Ena McIntyre – Garden Route Branch
A firm and virtually infallible favourite with landscapers and new home owners for many decades, the Ceylon Rose or Oleander secured a firm footing in the Western Cape before becoming a problem plant threatening the ecology of river valleys in our dry regions in particular. Its robustness, resistance to disease, tolerance of adverse soil and climatic conditions undoubtedly gave it the upper hand. Today its invasive status is a declared Category One special effect weed – competitive and poisonous. It is important to note that the category one status does not apply to sterile double-flowered cultivars.
On the coastal side of the Outeniqua and Tsitsikamma mountains there are isolated infestations of Nerium oleander (Oleander). However the main impact of this category one weed is in the watercourses in the semi-arid areas of the Little Karoo. Introduced from the Mediterranean area as a garden subject and as a screening plant we can still today see the excellent examples of Nerium oleander used as screening plants along the N1 between Cape Town and Paarl. Of particular importance is the fact that the primary invader is the pink flowered variety – clearly evident along the Nelsrivier outside Calitzdorp and the river valleys of the Kamanassie region. All parts of the plant are extremely toxic and lethal and the sap is a skin irritant.
Identification: The foliage is slender, leathery dark green leaves. Overall appearance is that of a large robust shrub (up to 6m tall) with an abundance of pink, red or white flowers. The fruits are red-brown in colour, split length-wise when ripe exposing the seeds that have tufts of hair.
Control: The plant coppices when cut back, complicating control. No specific herbicide is registered for the control of this invader weed. There are herbicides that are registered for total weed control which could be used. However, great care needs to be taken with their use to avoid damage to other species. The tufted seeds are wind and water dispersed, therefore recognising and weeding seedlings before they become too large is the best approach. Large plants need to be removed entirely.
Substitutes: We have any number of really stunning large indigenous shrubs that will do your garden justice - a few examples are: Buddleja salviifolia (Sagewood), Clerodendrum glabrum or c. myricoides (Cat’s whiskers/Tontelhout), Diospyros lycioides (Star apple), Dombeya burgessiae (Pink wild pear)
References: “ALIEN WEEDS AND INVASIVE PLANTS”: Lesley Henderson. Copyright © 2001 Agricultural Research Council.