Jubase1, Jorge L. Renteria2, David Maphisa1,3 and Ernita van Wyk4
1South African National Biodiversity Institute, South African National Biodiversity Institute, Private Bag X7, Claremont, 7735, Cape Town, South Africa.
2Department of Environmental Science and Policy, University of California, Davis, CA, USA
3Department of Statistical Sciences, University of Cape Town, South Africa
4ICLEI – Local Governments for Sustainability, Cape Town, South Africa
Naturalizing populations of Asphodelus fistulosus (onion weed), native to Europe, were recorded in South Africa for the first time during the early 1990s. This represents the first record of an invasive member of the Asphodelaceae family in South Africa. Initial records lodged in 2012 indicated the presence of two populations. Further surveys and public awareness raising initiatives led to the discovery of five more populations between 2012 and 2016. All known populations occur along roadsides but in other parts of the world the species has demonstrated the ability to spread into adjacent native vegetation and crop fields. Population sizes vary from 4m2 to 486m2 and plant density varies from13 plants/m2 to 4310 plants/m2. Randomized fixed plots were used to monitor the response of A. fistulosus populations to mechanical and chemical control and to track spread over time. Results over a four-year period suggest that suppression of reproduction is possible (age at reproduction is six months) and both mechanical and chemical control were effective. As the plant is highly detectable and control methods are effective, we believe existing naturalized populations can be extirpated with persistent effort. There is substantial uncertainty in terms of knowing whether all naturalized or cultivated individuals have been found. This limits the suitability of the species as a national eradication target. However, based on the invasive risk it poses and given encouraging results from extirpation effort as shown in this study, we conclude that site-specific extirpation is a feasible management goal for this species.