The Vice-Chancellor, Prof Sizwe Mabizela cordially invites you to attend the Inaugural lecture of Professor Julie Coetzee.

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Title and abstract

Hoping on a hopper: the silver bullet for water hyacinth control?

Water hyacinth, the world’s worst aquatic weed, plagues many of South Africa’s waterbodies, and has been the subject of much research for decades. Most of my 25 year research career has focused on understanding the bottom-up effects on top-down regulation of this weed. Nutrients, the main bottom up driver, result in enriched waterbodies that promote the growth of water hyacinth, to the detriment of control measures, including biological control, the most important top down driver. Biological control agents are herbivorous, host-specific insects whose feeding activity reduces the vigour of the target weed, resulting in control. South Africa has released more control agent species against water hyacinth than anywhere else in the world, however, when water bodies are as polluted as South Africa’s are, the efficacy of biological control is reduced. Cold winter temperatures on the Highveld also impact the level of control. In recent years, our approach to biological control of water hyacinth has shifted from classical biological control to inundative control, with the support of local stakeholders at invaded sites, in an attempt to increase the top-down pressure from herbivory on a bottom-up driven invader. A planthopper, Megamelus scutellaris, has provided spectacular results since its release in 2018 at Hartbeespoort Dam, a system plagued by water hyacinth for decades. Here I showcase these results.