Johannesburg: Rand Water has appointed the Centre for Biological Control (CBC) to assist with biocontrol efforts on the Vaal River Barrage reservoir. The collaboration aims to manage the invasive alien plants, Pontederia crassipes, commonly known as water hyacinth, and Pistia stratiotes, or water lettuce, which have become a significant concern in the region.
According to South African Government News Agency, Rand Water serves as the implementation agent for the integrated control and management of these invasive species. The organization highlighted that both plant species are highly invasive, with water hyacinth posing a more severe threat due to its resilience and aggressive nature.
In early 2024, a surge in the growth of these plants was observed on the Vaal River Barrage reservoir. This growth was attributed to a combination of factors, including nutrient-rich effluent spills, hot summer conditions, and reduced water flows. At its peak, the invasive plants covered approximately 397 out of the 940 hecta
res monitored under Rand Water’s contract. However, through public and local community efforts, along with pro-bono assistance from Rhodes University’s CBC, the plant mass was significantly reduced to less than 100 hectares.
Rand Water managed to further decrease the cover to less than 1 hectare by the beginning of spring. The organization acknowledges that long-term efforts are necessary due to the persistent nature of the plants and the existing seed bank in the water. An integrated approach combining various mechanisms such as physical removal, chemical spraying, water course curtaining, and biocontrol agents has been adopted to manage the issue effectively.
The CBC is the sole institution in South Africa with the expertise, facilities, and network to provide comprehensive support for biocontrol. Led by Professor Julie Coetzee and Dr. Kelby English, with additional support from Professor Martin Hill, the CBC team will oversee all aspects of biocontrol for the project.
Rand Water announced that four perm
its have been granted by the Department of Forestry, Fisheries, and Environment to rear biocontrol agents. These agents will be nurtured at Rand Water’s nursery and three community sites, with funding for community sites sourced directly from local communities. The biocontrol agents, which include the water lettuce weevil Neohydronomus affinis, water hyacinth hopper Megamelus scutellaris, and water hyacinth weevils Neochetina bruchi and N. eichhorniae, have undergone rigorous testing to ensure they are host-specific before their release in South Africa.