The exotic vine Dolichandra unguis-cati (formerly Macfadyena unguis-cati) is a woody, evergreen creeper that has become a significant threat to biodiversity in many sensitive ecosystems around South Africa. The vine is originally native to central, and tropical South America, including the West Indies, but has become invasive in a number of regions of Southern Africa, Australia, New Zealand, India, Mauritius, China, New Caledonia and the USA, including Hawaii. This extensive range has been facilitated through the horticultural trade which distributed the plant as an ornamental. Showy yellow flowers coupled with its climbing habit made the fast-growing creeper ideal as a hedging plant or natural screen for unsightly walls and buildings. The plants' ability to 'climb' is facilitated by its distinctive leaves which consist of two leaflets and a modified three-forked tendril. Each tendril is tipped with a tiny hardened hook which can attach to most surfaces enabling the vine to grow up walls, tree trunks and over other vegetation. It is these tendrils that resemble claws and the feature from which the plant draws its name.
Within South Africa, although spreading, cat's claw creeper is considered to be in the early stages of invasion due to its relatively small distribution. Nevertheless, the weed has formed some very dense infestations in Gauteng, Kwazulu-Natal, Limpopo, Mpumalanga and the North West. Within these provinces the weed has become a significant invader of cultivated orchards and plantations, riparian corridors, natural forest remnants and disturbed areas such as roadsides and urban spaces. Vigorous growth allows the vine to sprawl over other vegetation and, through a combination of both shading and weight, it can kill even the largest canopy trees. In the absence of climbing support, individual stems grow along the ground resulting in a thick carpet which precludes the growth and seed germination of indigenous understorey vegetation.
Due to the problems associated with cat's claw creeper infestations, D. unguis-cati has been declared a category 1b weed in South Africa in terms of the Alien and Invasive Species Regulations (AIS), National Environmental Management: Biodiversity Act (Act No 10 of 2004), which necessitates its control or eradication where possible. No trade or planting is allowed. The management of cat's claw creeper is, however, extremely difficult and little has been achieved with either mechanical or chemical control. Control is hampered by the weed's extensive vegetative growth, profuse seed production, and the presence of subterranean root tubers. Individual stems growing along the ground readily develop roots and tubers wherever nodes touch the ground and can develop into new plants if separated from the parent plant. The presence of tubers therefore, makes infestations extremely resilient as they will readily resprout if above ground parts are damaged or removed, for example via mechanical weeding, fire, or herbicide application. Chemical control, and in particular the use of broadleaf herbicides, is further complicated by the potential for non-target effects to the sensitive or economically important ecosystems that the weed normally invades. Due to these constraints, as well as the prohibitive costs associated with manual and chemical control, weed management practitioners have prioritized biological control as the only practical and long-term solution to cat's claw creeper infestations.
The biological control programme against cat's claw creeper was initiated in 1996 by the Agricultural Research Council's Plant Protection Research Institute and has been sustained through collaboration with the Working for Water Programme (Department of Environmental Affairs: Natural Resource Management Programmes). To date, this programme has investigated seven potential insect biocontrol agents and released four into the country. Feeding from these species on the leaves of cat's claw creeper significantly reduces the amount of area available for photosynthesis. Additionally, at high populations, feeding damage causes premature leaf drop and the die-back of shoot tips, severely hampering the growth of the weed. Research is currently focussing on getting these biocontrol agents established at as many cat's claw creeper infestations around South Africa as possible, as well as evaluating their impact to the plant, and identifying factors that could be influencing this interaction. In conjunction with this work, two additional insect species, the leafhopper Neocrassana undata, and the seed feeding weevil Apteromechus notatus, are also being investigated within quarantine in order to determine their suitability for future introduction as biocontrol agents against the weed. In this way, biological control will address both the negative aspects of already established cat's claw creeper infestations through the use of multiple leaf herbivores, as well as the future spread of the weed with the use of a specialist seed feeder. In light of the achievements to date and continued financial support of this programme, the prospects for biological control of cat's claw creeper in South Africa are good.
A review of this biological control programme was published in 2011 pdf
The following fact sheets can be downloaded:
Contact person: Anthony King, E-mail: KingA@arc.agric.za