Water hyacinth – an invasive species considered the worst weed in the world, literally brings shudders to local municipalities and ordinary South Africans who are invested in preserving our dams and water sources. Originally from the Amazon Basin, this plant has spread rapidly across various water bodies in the country, particularly where nutrient-rich waters provide ideal growing conditions. Once the plant invades, it forms dense mats that completely cover the water’s surface, impacting the life of any other organisms around it. The concern about the plant is that its seeds remain viable in the soil for more than 20 years, which means it can keep propagating – we’ve seen its terrible impact on Hartbeespoort Dam and the Vaal River.
There are other dams where the plant is out of control too – specifically Benoni’s Middle Lake and Civic Lake, where the fight to keep the waters clear has been going on for years. Luckily, there is a solution, and as cute as they sound, planthoppers are reducing the cover of the invasive plant significantly.
What is a planthopper?
Aside from being tiny superheroes, adult planthoppers (known scientifically as Megamelus Scutellaris) are small sap-sucking insects, about 3 mm long, with colours ranging from pale cream to dark brown. Reared in mass quantities during the spring, these little soldiers feed off the sap of the Hyacinth plant by piercing the plant tissue and damaging the cells, which essentially makes the plant rot and sink. Once the water hyacinth starts to rot, it has no chance of regenerating – fantastic news for dam preservation!
The best part about planthoppers is that adults can be reared, so essentially we can rear as many as we need in a biological control agent rearing station and then unleash them in droves across water hyacinth to do their impactful job.
Planthopper rearing facilities
FSG is proud to be a part of building the incredible rearing facilities that bring planthoppers to life. The rearing stations are built to create the exact same conditions in the Amazon basin (hot and humid!) where the planthoppers are from. This is the catalyst for increasing their population in very short time spans – development from egg to adult occurs over about three weeks. The rearing stations are like greenhouses, made of half-circle tunnels with a metal-framed structure, which is then covered with protective plastic. Specialised breeding boxes are also constructed.
Thanks to these fantastic facilities, planthopper releases on Middle Lake began in November 2023, with the population steadily increasing and reaching 3525 planthoppers per m² by early 2024 – a promising start despite the initial releases being considered late in the season.
This winning strategy is the same one used to fight the plant invasion at Hartebeespoort Dam, where intensive and repeated planthopper releases from early spring and over summer 2023/2024 reduced the cover from approximately 35% in peak summer to 5% in March 2024. Planthopper densities at this time approximated 10,000 per m². Since the establishment of rearing stations and repeated releases began in 2019 at Hartbeespoort Dam, cover has been reduced to less than 5% every year.
Long-term and effective
FSG’s efforts to assist in building these tunnels, along with the help of the Centre for Biological Control and Rhodes University, will cement the project’s long-term success. Even with the risks of water hyacinth propagation, the community will be able to continue the positive trajectory of eradicating the harmful plant and get Benoni’s dams back to health once again.
When it comes to handling a task as challenging as the water Hyacinth invasion, managing the impact would be impossible without the help of dedicated teams who are all specialists in their particular fields. The FSG team has taken the challenge in their stride and become a pivotal part of the solution.
Raising a child takes a village, as does rearing hundreds of thousands of planthoppers. We’re proud to be part of the village and look forward to continuing to fight against the waterweed.
