Center for Biological Control appointed to assist with invasive alien plants

Rand Water has engaged the Center for Biological Control to assist with the biological control of the Vaal River Barrage.

Rand Water is the implementing agent for the integrated control and management of the invasive alien plants – Pontederia crassipes (water hyacinth) and Pistia stratiotes (water lettuce) – at the Vaal River Barrage reservoir.

It said both plant species were extremely invasive, with water hyacinth being more resilient and aggressive than water lettuce.

“In early 2024, the Vaal River Barrage reservoir experienced explosive growth of the two species, fueled by the perfect storm of nutrient-rich wastewater release, hot summer conditions and reduced water flows in the system.”

“At the peak of the spread, water surface cover had reached approximately 397 of the total 940 hectares monitored under the contract,” Rand Water said.

Due to public and local community involvement in the physical removal and pro bono support from Rhodes University – Center for Biological Control (CBC) at the time, Rand Water said the area has been reduced to less than 100 hectares and further work is underway The company, as part of the contract with the Ministry of Water and Sanitation, has physically removed additional plants during the winter months when the plants are dormant.

The company said coverage was currently less than 1 acre as of early spring.

Rand Water noted that the work would have to be long-term due to the nature of the plants and the seed bank already present in the water.

“It was also identified that an integrated approach was required to carry out this work. The integrated approach adopted involves the use of various mechanisms; physical removal, chemical spraying, stream curtaining and biological control agents.

“The CBC is the only facility in South Africa that has qualified specialist staff, biocontrol breeding facilities and a network of teams that can provide on-site assistance in the form of advice, implementation support and long-term monitoring techniques,” the entity said .

The CBC has been appointed as the sole service provider for the upcoming season to assist in all aspects of biocontrol and support the project. The team is led by Professor Julie Coetzee and Dr. Led by Kelby English and additionally supported by Professor Martin Hill.

Four approvals for hedge biocontrol agents granted

Through approval from the Ministry of Forestry, Fisheries and Environment, Rand Water said four permits were issued for biocontrol cultivation at the company’s nursery and three community sites, with funding for community nursery sites coming directly from the community.

“The aim is to use biocontrol agents as much as possible to control the two invasive alien plants associated with physical removal, and only where other methods do not work quickly enough will the use of approved herbicides be used.”

“All biocontrol agents released were thoroughly tested and confirmed to be host specific before being approved for release in South Africa. This means that the pathogens feed exclusively on their target host plants and complete their life cycle there,” said Rand Water.

The four biocontrol agents will be the focus of the rearing facilities, including the water hyacinth weevil Neohydronomus affinis, the water hyacinth beetle Megamelus scutellaris and the water hyacinth beetles Neochetina bruchi and N. eichhorniae. – SAnews.gov.za