The role of eutrophication of waters in the management of Eichhornia crassipes in South Africa
South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of inappropriate water treatments (use of unnecessarily high doses of phosphorus in the 1970s). In addition, to satisfy the water demand, large impoundments (e.g. dams, reservoirs) and weirs in rivers have been constructed. This has reduced the flow in the rivers, creating still or slow-moving water bodies that are ideal for aquatic plant invasions. In these conditions, Eichhornia crassipes (Pontederiaceae, EPPO A2 List) has become highly damaging despite the implementation of a biological control programme in South Africa.
An analysis of published and unpublished laboratory studies investigated the combined effects of phosphorus and nitrogen water nutrient concentration and of the following biological control agents: Cornops aquaticum (Orthoptera: Acrididae), Eccritotarsus catarinensis (Heteroptera: Miridae), Neochetina bruchi, N. eichhorniae (Coleoptera: Curculionidae), Sameodes albiguttalis (Lepidoptera: Crambidae), Orthogalumna terebrantis (Acari: Galumnidae). This review showed that water nutrient status was more important than the presence or absence of biological control agents in influencing E. crassipes growth, and this was also confirmed by long term field data analysis.
The first step in any E. crassipes control programme should therefore be to reduce the phosphorus and nitrogen content of the water body.
Sources
Coetzee J ; Hill M P (2012) The role of eutrophication in the biological control of water hyacinth, Eichhornia crassipes, in South Africa. Biocontrol 57(2), 247-261.