Professor’s inaugural lecture on winning the hyacinth invasion on Hartbeespoort Dam

Prof Julie Coetzee of the Rhodes University delivered her inaugural lecture on the fight against the hyacinth on Hartbeespoort Dam last week to honour her achievement of the title of Professor.

Professor Julie Coetzee

Prof Coetzee has been working actively to combat the hyacint infestation on the dam since 2019. Through her work with the Centre for Biological Control (CBC), where she serves as its Aquatic Weeds Programme Manager and Deputy Director, she coordinated a mass-rearing programme of the Megamelus, which were then released into the dam throughout 2019, with excellent results.

Her research biological control systems started in 2005 when she and others conducted research that showed that in all the water bodies where they had observed water hyacinth growing, they found high amounts of nutrients (phosphorus and nitrogen) that contributed to the rapid propagation of the weed in our country’s waters. She attributed this high nutrient saturation to a lack of water purification infrastructure and lax water policy that fosters nutrient-rich environments ideal for the invasive water hyacinth plant. The water hyacinth has no natural competitors in our ecosystem and is thus in the best position to take full advantage of those eutrophic water conditions and spread rapidly.

According to Professor Coetzee, the solution is to introduce those competitors into the ecosystem to act as biological control agents and exert top-down pressure on the invader. This is not a new concept even in combating water hyacinth in South Africa, with various bugs, mites, moths and fungi being migrated from South America (where water hyacinth itself originated) to try to get a grip on the weed. Unfortunately, the high amount of nutrients in the water, combined with the inability of most of the introduced control agents to survive the colder winters in South Africa, has thus far rendered most of these efforts only partially successful, although her most recent work, however, has yielded promising results.

Through the efforts of the CBC’s Sisonke programme, various schools and community groups in the area surrounding Hartbeespoort Dam, she and her team reduced the water hyacinth coverage on the dam from 42% to under 2%. Professor Coetzee spoke of the work that still needs to be done, particularly with the population reduction Megamelus experiences during winter. However, the results of this augmented biological control programme have already far exceeded her expectations and have garnered a great deal of local and international attention.

Prof Coetzee and her team are currently working on finding a biological control programme for the invasive salvinia weed on the dam.