Rotary, WESSA sponsor net to remove salvinia from Hartbeespoort Dam

Rotary Brits Hartbeespoort, in conjunction with WESSA, donated a specialised net to the community in an attempt to speed up the manual removal of the invasive salvinia weed on the Hartbeespoort Dam.

The new net to remove the invasive salvinia was used for the first time last week.

The Harties Boat Company for the first time used the net on Thursday and according to Dion Mostert, owner of the boat company, they were able to remove much more weeds than with previous efforts.

“However, some fine-tuning will have to be done as a significant amount of salvinia still slips through the net,” said Johan Wesson, of WESSA and a member of Rotary Brits Hartbeespoort.

The boat company and estates around the dam have joined forces and have been working for the past months to remove the salvinia weed. Pecanwood are scooping the weeds in their harbour and have already taken out tons of weeds with a TLB with an adapted scoop.

“Salvinia minima, or common salvinia, is currently covering 25% of Hartbeespoort Dam,” Rhodes University’s Centre for Biological Control (CBC) said. “We are working hard to get the potential control agent, Cyrtobagous salviniae, released if it proves to be suitably host specific.”

Salvinia minima, a ‘floating fern’ is native to South America, and is also highly invasive throughout southern America.

According to Dr. Julie Coetzee, deputy director at the CBC this plant was first spotted by entomologist and biocontrol scientist Dr Carina Cilliers, when she noticed an unusual floating plant on the banks of Hartbeespoort Dam. The floating plant was later identified by fern taxonomist Dr Ronell Klopper of SANBI as the invasive Salvinia minima.

“Since then, common salvinia on the dam has been largely inconspicuous due to the presence of water hyacinth. The proliferation of common salvinia, just as water hyacinth came under biological control through the combined efforts of the Centre of Biological Control (CBC) and invested parties around the dam, is no coincidence. In areas that experience high levels of nutrient inflow (pollution), the control of one aquatic weed opens resources to other potentially invasive plant species creating a ‘secondary invasion event’. In the case of common salvinia, the ‘secondary invasion event’ is taking place just as resources such as light availability, space and nutrients, otherwise used by water hyacinth, have become available.”

She advised that it is vitally important that the spread of this weed is prevented. Boating, fishing, and other recreational water sport gear must be cleaned if they are to be used on other waterbodies in South Africa. There is already confirmation that common salvinia is downstream of Hartbeespoort on Roodekoppies Dam, as well as on Roodeplaat Dam.