South Africa Scores a Century
Chain-fruit cholla (Cylindropuntia fulgida var. fulgida) is one of the cacti under complete control in South Africa since the establishment of a cladode sucker (Dactylopius tomentosus) (inset). Image - Hildegard Klein
Biocontrol of weeds got underway in South Africa in 1913 with the introduction of a cochineal insect (Dactylopius ceylonicus) to combat an invasive cactus called drooping prickly pear (Opuntia monacantha). It was to be the start of great things.
Drooping prickly pear was within a few years brought to its knees, and has remained under control ever since. This inaugural project gave many the impression that weed biocontrol was quick and easy, when in fact most projects have required years of careful research, with no assurance of success, and a long wait for benefits to be realised. One hundred and six species of biocontrol agents have now been released against 48 plant species resulting in the establishment of 75 species.
“There have been some pretty spectacular successes against a range of weeds but in particular aquatic plants, cacti, and trees have proven amenable to this approach,” concluded John Hoffmann of the University of Cape Town. Because a number of invasive trees in South Africa provide important social and commercial benefits (e.g. firewood, shade, fodder and timber) only agents that target the reproductive structures have been released. “This allows the trees to remain and be used while preventing unwanted spread,” explained the chair of the 14th ISBCW, Fiona Impson. Twelve weeds are now considered to be under complete biological control, and a further 20 are under substantial control (see table pg 6). Cost–benefit analyses confirm that investment in weed biocontrol in South Africa is reaping some remarkable returns. A recent analysis suggested the most modest cost–benefit ratio was a still highly respectable 1:8 for red sesbania (Sesbania punicea) with the highest a whopping 1:3726 for perennial invasive Australian trees, with cacti not too far behind on 1:2731.
Just as important as achieving success has been the lack of negative consequences. No significant damage to crop plants or native species has occurred as a result of the released agents. Despite this record of success and safety the South African weed biocontrol programme, like many others internationally, began in the 1980s to suffer from an escalation in exaggeratedly risk-averse attitudes and restrictive political structures and processes for gaining approval to release new agents. This meant that during the past decade the release of new agents nearly ground to a halt. However, fortunately during the centenary year, common-sense has prevailed with key agencies (Department of Agriculture, Fisheries and Forestry; Department of Environmental Affairs, and the South African National Biodiversity Institute) reactivating a peer-review process for assessing release applications. “This has allowed a protracted stalemate to be broken and for new agents to again be approved and released,” confirmed John.
A hallmark of the successful South African biocontrol programme is interagency collaboration and cooperation to make the best use of resources. The Working for Water (WfW) programme (set up to clear catchments of woody vegetation, along with providing social benefits like employment), Plant Protection Research Institute, and South African universities work closely together on weed biocontrol programmes together with local and national conservation bodies. “Quarterly technical liaison meetings, workshops and also a planning meeting attended by 70–100 participants are held annually,” said Fiona. The WfW programme, which provides most of the funds for weed biocontrol activities in South Africa, has recently engaged a new partner to help out. The South African Sugarcane Research Institute, which rears many biocontrol agents for insect pests of sugar cane, has expanded its scope to mass-rear weed biocontrol agents, allowing greater numbers to be produced and released more rapidly. With an estimated 20 million hectares of land in South Africa infested with unwanted plants there is still much to be done. Fortunately increased funding has been made available and overall, as the rainbow nation moves into its second century of weed biocontrol activity, the future appears bright.
Contact:
John Hoffmann
john.hoffmann@uct.ac.za