More biocontrol agents released in the Vaal

On Saturday 24 February, over 10 000 biocontrol agents were released  in the Taaibosspruit by Rand Water alongside the Rhodes Center for Biological Control – both upstream and downstream  – . “The action is augumenting the integrated strategy to halt the spreading of water lettuce on the Vaal River, by constantly releasing  biocontrol agents to increase their population, Rand Water  in a post on their Facebook page said over the weekend. .

Water lettuce is a poisonous and highly invasive free-floating freshwater weed found in water bodies and slow-moving waterways in warm regions. It was first seen in SA in the Suikerbosrivier in 2021.

According to Prof. Julie Coetzee from the Rhodes Centre for Biological Control, these insects can effectively control this floating invasive species. Positive feedback is that weevils which were originally released in the Leeuspruit a few years ago, are breeding well there and have caused damage to much of the water lettuce there.

The latest release included over 8 000 Megamelus scutellars individuals, and 2 000 Neohydronomus  affinis individuals, as well as 600 individuals of the Neochetina species, Rand Water said.

Weevils and hoppers were also realesed into the Vaal River on 15 February.

Over 400 weevils were then released to halt the growth of water lettuce (Pistia Stratiotes). The small weevils eat water lettuce, while hoppers eat hyacinth.

The increasing incidence of water lettuce in the Vaal River can have a devastating impact  that range from fishing (which poorer communities need to provide a meal) to agriculture, where irrigation equipment clogs, environmental devastation, loss of tourism potential, job creation, property development and local economies.

Vaal River Rats SA over the weekend once again encouraged the community to participate in removing the water lettuce manually. “The people have been nothing short of incredible through this process,” the organisation said.