Economic evaluation of chemical and biological control of four aquatic weeds in South Africa

ABSTRACT

Invasive alien plants (IAPs) pose a threat to biodiversity and the economy of the countries they invade. In South Africa, the Department of Environment, Forestry and Fisheries, Natural Resources Management Programmes, previously The Working for Water Programme (WfW) is tasked with controlling IAPs in a way that protects the environment, as well as producing maximum return to society through poverty alleviation. Biological control is one of the management tools used to control IAPs in South Africa. Four aquatic weeds, Pista stratiotes, Salvinia molesta, Azolla filiculoides and Myriophyllum aquaticum, are under complete biological control in South Africa. However, in the absence of biological agents, the WfW programme would have used herbicides to control these weeds. This paper presents a retrospective analysis of the relative herbicide cost-saving associated with the use of biological control instead of chemical control. The study used cost benefit analysis (CBA) framework with an 8% discount rate. The estimated cost of the biological control on all four aquatic weeds was about R7.8 million, while the estimated cost of chemical control to achieve the same level of control varied between R150 million and R1 billion, depending on the method of application and number of follow up operations. Benefit to cost ratios varied between 90:1 and 631:1, again depending on method of application and number of follow up sprays. The results remained robust under a 5% and 10% sensitivity test and show that biological control is the most cost-effective management option for aquatic weeds in South Africa.

KEYWORDS:

• Invasive alien plants
• cost benefit analysis
• cost-effectiveness
• herbicide cost-saving
• working for water

Acknowledgements

Research on biological control of invasive plants in South Africa is funded by the Department of Environmental Affairs, Natural Resource Management Programme, (previously the Working for Water Programme). The South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa provided further funding. Any opinion, finding, conclusion or recommendation expressed in this material is that of the authors, and the National Research Foundation does not accept any liability in this regard.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Department of Environmental Affairs, Natural Resource Management Programme; National Research Foundation of South Africa; The South African Research Chairs Initiative of the Department of Science and Technology.