​​​​​​There are various means of managing invasive alien plants:

1. Mechanical control

This entails damaging or removing the plant by physical action. Different techniques could be used, e.g. uprooting, felling, slashing, mowing, ringbarking or bark stripping. This control option is only really feasible in sparse infestations or on small scale, and for controlling species that do not coppice after cutting. Species that tend to coppice, need to have the cut stumps or coppice growth treated with herbicides following the mechanical treatment. Mechanical control is labour intensive and therefore expensive, and could cause severe soil disturbance and erosion. Read more about mechanical control in the ARC-PHP publication Rehabilitation recommendations after alien plant control by Peta Campbell (order from Andrew Mfolo). Contact Jeremy Goodall for more information on mechanical control measures.

2. Chemical control

Chemical control involves the use of registered herbicides to kill the target weed. ARC-PHP's research on the chemical control of plant invaders is aimed at developing safe, selective and affordable herbicide treatments which will provide effective control in a wide range of environmental conditions and which are compatible with biological control. The Division also tests herbicides for registration purposes. Contact Jeremy Goodall for more information.

Further reading:
  • Two ARC-PHP publications: Rehabilitation recommendations after alien plant control and Wattle Control, both by Peta Campbell (order from Andrew Mfolo)
  • A 2007 publication by the Registrar (Act No. 36 of 1947): A Guide to the Use of Herbicides of Bush Encroachment, Noxious Plants and Aquatic Weeds, obtainable from tel. +27 12 319 7141 or fax +27 12 319 7260.
  • The Working for Water Programme's website www.dwaf.gov.za/wfw/Control/docs/controltables.doc

3. Biological control

Biological weed control consists in the use of natural enemies to reduce the vigour or reproductive potential of an invasive alien plant. Research into the biological control of invasive alien plants is the main activity of the Weeds Research Programme of ARC-PPRI. ​​​​

Read more about the important role the Working for Water Programme plays in the biological control of invasive alien plants in South Africa. 

To obtain biocontrol agents, the biocontrol implementation officers of the National Resource Management Programmes (NRMP) within the Department of Environment Affairs (DEA), previously known as the Working for Water Programme,​ can be contacted. Alternatively, contact the provincial representatives of the  Directorate: Land Use and Soil Management (LUSM)​, Department of Agriculture, Forestry and Fisheries (DAFF)​. Bioocontrol agents ​for all cactus species can be obtained from the Uitenhage ​mass-rearing station of the Centre for Biological Control, Rhodes University, by contacting Dr Iain Paterson​.

More information

​The following documents can be downloaded:

4. Mycoherbicides

A mycoherbicide is a formulation of fungal spores in a carrier, which can be applied to weeds in the same way as a chemical herbicide. The spores germinate on the plant, penetrate the plant tissues and cause a disease, which could eventually kill the plant. Mycoherbicides are indigenous to the country of use and therefore are already naturally present in the environment. Under natural conditions they do not cause enough damage to the weed to have a damaging impact. They are therefore mass produced and applied in an inundative inoculation, using herbicide application equipment, which leads to an epidemic of the disease knocking the weed population down. They can’t maintain the epidemic under natural conditions, and need to be re-applied at regular intervals. Because mycoherbicides are indigenous but only cause low levels of disease under natural conditions, they do not pose a risk to non-target plants.

Considerable progress has been made in this field with the development of a mycoherbicide from naturally occurring pathogens which is used in the control of both hakea seedlings and mature plants (Hakatak). Research is underway to develop a mycoherbicide against rooikrans. A number of fungi have the potential to be developed as mycoherbicides against water hyacinth and mesquite, and some research was done towards this goal in the past. An innovative first for South Africa was the development of a non-pathogenic fungal inoculant to prevent regrowth of stumps of black and golden wattle after felling (Stumpout).

There are a number of important differences between mycoherbicides and all the other biocontrol agents that have been introduced against alien invasive weeds in South Africa (referred to as classical agents). These are compared in the following table:

 

Classical agents

Mycoherbicides

Introduced from the country of the plant’s originIndigenous to the country where the plant is a weed
Co-evolvedNew association
Once introduced, population of agent increases and spreads with minimal human aidNaturally cause low levels of disease and must be intensively produced and applied on a regular basis
For safety reasons only host specific agents allowed to be releasedMay have a wide host range but no risk to other plants as it can’t maintain damaging levels

 

5. Integrated control

Frequently it is advisable to use a combination of two or more of the control method mentioned above. This is known as integrated control. Biological control can be integrated into conventional management plans with great success, provided that the requirements of the biocontrol agents are kept in mind, and provision is made for their continued survival in the affected area.

Management of specific invasive alien plants in South Africa

Information on ARC-PPRI's research into the control of various invasive alien plants in South Africa is available on our website, by selecting from a list of either botanical names or common names.

Training

If you want to qualify yourself as a Pest Control Officer for Environmental Weed Control, you could register for the course entitled Environmental Weed Control, presented by Dr Graham Harding, using content supplied by ARC-PHP.
(Contact e-mail: harding@pixie.co.za)