Biological control of invasive alien plants involves the use of agents introduced from the country of origin (plant-feeding insects and mites, and plant pathogens) after rigorous testing under quarantine conditions to ensure that they do not pose a substantial risk to any agricultural crop or indigenous plant species. Release applications are extensively scrutinised. The biological control of invasive alien plants, using plant-feeding insects and mites, and pathogens, is an attractive management option because: (i) it is relatively cheap and very safe compared with the costs and risks associated with herbicide development and deployment; (ii) biological control can be successfully integrated with other management practices; (iii) biological control agents can often (though not always) disperse to and control plants in otherwise inaccessible areas; and (iv), most compelling of all, biological control is self-sustaining. Without biological control, invasive alien plant management would be beyond the capabilities and resources of South Africa. For biological control to be integrated with other control measures it is crucial to understand the impact of the agents. This requires pre- and post-release evaluation of the target plant. This has too often been assigned a low priority, and once an agent was released, researchers were redeployed to work on new agents. Some agents also need to be manually redistributed around the country or repeatedly released for control to be achieved.

Many alien plant species invade areas that are rugged and inaccessible, especially in mountain areas, but these need to be prioritised for control in many cases. Studies have shown that an individual plant on an exposed slope or mountain top can contribute more to increases in the area invaded than do all the plants in a hectare of dense infestation in a lowland, as seeds from a single isolated plant on a mountain top will be dispersed much further and over a wider area. This suggests that plants in inaccessible areas need to be cleared as they would otherwise provide a constant source of seeds that would drive re-invasion of more accessible areas that have been cleared. In order to deal with this problem, the Working for Water programme has trained, equipped and deployed teams of workers to clear cliff faces and other inaccessible areas across the country (so-called “high-altitude teams”). To date there has been no assessment of how effective this approach has been, but high-altitude teams plan and execute tasks independently of other control operations. However, if planned and executed in collaboration with adjacent projects, the approach offers a solution to the problem of dealing with invasive alien plants in inaccessible mountain areas.

The intended outcome for emerging weed control is the identification and assessment of newly established invasive alien species, or species with limited distributions, and eradication of species where feasible and desirable.

The Eco-Furniture Factories Programme seeks to make optimal use of some of the biomass cleared by Working for Water in creating work opportunities to make products that help Government to meet its needs, and notably the pro-poor opportunities within this. Five Eco-Furniture Programme factories have been established. The programme makes products that government needs from wood obtained from the clearing of invasive alien trees. The programme also intends to promote the general use of biomass through biogas digesters, in providing energy and jobs to the rural poor. In addition, there is potential to use wood chips from invasive trees and shrubs to make wood-wool cement board fibre, which might be highly competitive in dealing with the need for housing, and other buildings. All these interventions are politically attractive, as they address multiple needs. Their potential to enlarge the pool of funding available for managing biological invasions is substantial.

The intended outcome of aquatic weed control is preventing the erosion of, or restoring, ecosystem services, biodiversity, and ecological integrity in freshwater ecosystems. Water hyacinth (Eichhornia crassipes), a South American aquatic weed introduced widely into Africa, has blocked waterways limiting boat traffic, access to safe water and fishing. Water hyacinth also blocks sunlight and oxygen, dramatically altering biological diversity in aquatic ecosystems.