Original Research

Evidence that residues of tebuthiuron arboricide present in soil of Mokala National Park can be phytotoxic to woody and grass species

Carl F. Reinhardt, Hugo Bezuidenhout, Judith M. Botha
Koedoe | Vol 64, No 1 | a1658 | DOI: https://doi.org/10.4102/koedoe.v64i1.1658 | © 2022 Carl F. Reinhardt, Hugo Bezuidenhout, Judith M. Botha | This work is licensed under CC Attribution 4.0
Submitted: 04 October 2020 | Published: 18 March 2022

About the author(s)

Carl F. Reinhardt, Unit for Environmental Sciences and Management, Faculty of Natural and Agricultural Sciences, North-West University, Potchefstroom, South Africa; and, Department of Plant and Soil Sciences, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
Hugo Bezuidenhout, Nature Conservation, Scientific Services, SANParks, Kimberley, South Africa; and, Applied Behavioural Ecology and Ecosystem Research Unit, Department of Conservation, University of South Africa, Johannesburg, South Africa
Judith M. Botha, Scientific Services, SANParks, Skukuza, South Africa

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Mokala National Park (MoNP) has a history of arboricide use through South African National Parks (SANPs) having bought commercial game farmland for its establishment in 2007. Tebuthiuron arboricide is known to have been applied for controlling bush densification during the period 1996 to 2004. Persistent negative impacts on MoNP vegetation, which are ascribed to the historical arboricide use, have prompted this investigation from 2016 to 2017. Bioassay experiments employing as test plants the tree species Vachellia erioloba and Vachellia tortilis, the shrub species Senegalia mellifera and the grass Tragus berteronianus were conducted in a glasshouse. Growth responses of these species were assessed upon their exposure to a tebuthiuron concentration range that simulated expected levels in MoNP soil soon and long after application. Chemical analysis as well as bioassay with the test species Lycopersicon esculentum (tomato) were performed on soil samples collected from three depths (0−30, 30−60 and 60−90 cm) of the soil profile at two sites in MoNP where tebuthiuron was applied in the past. The three woody test species showed differential, negative growth response to tebuthiuron, and even growth of the grass species (T. berteronianus) was affected at the higher concentrations. Evidence provided by the tomato bioassay and analysis performed on soil samples collected in situ points to the putative presence of tebuthiuron, more than a decade after the last use of arboricides for controlling bush densification.

Conservation implications: If the reported evidence of the presence of phytotoxic residue of tebuthiuron in soil of MoNP would be substantiated through further research, such findings could at least partly explain the failure of natural recruitment of vegetation in those areas where the woody component was degraded because of arboricide application more than a decade ago.


arboricide; bush densification; ecosystems; environment; herbicide residues; problem plants; soil contamination


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