Managing waterhyacinth invasion through integrated control and utilisation: perspectives for lake Victoria.
Achieving control of the biological invasion of water hyacinth (Eichhornia crassipes) in Lake Victoria has become a major priority in East Africa. Water hyacinth was first introduced to Egypt in about 1890, but its spread upriver was restricted. A later introduction in 1942 resulted in its spread along the entire length of the Congo River within 14 years and it is believed to have crossed into the upper Nile shortly thereafter. Integrated management of water hyacinth consists of chemical and biological control, and mechanical and manual clearance. The smooth water hyacinth weevil (Neochetina eichhorniae) is widely utilised in biological control programmes throughout the tropics and sub-tropics, including East Africa. This insect was observed feeding on banana, cabbage and vanilla under laboratory conditions, but did not deposit eggs into these crop plants as it does with water hyacinth. The herbicide 2,4-D is commonly employed for chemical control. Mechanical and manual clearance occupies an important role as an emergency measure, especially in the decongestion of harbours and hydroelectric reservoirs. The Owen Falls hydroelectric facility on the River Nile (Uganda) is currently protected from waterhyacinth by mechanical harvesting using four push boats with front-mounted hydraulic rakes and two floating conveyer belts. Water hyacinth may be used as an organic input to soils, livestock feed, a source of crude fibre, a substrate for biogas generation and in waste water treatment. Water hyacinth is rich in plant nutrients, particularly phosphorus and potassium, but its high moisture content (95%) restricts recovery and transport. Fresh water hyacinth offers less potential as an animal feed than when it is ensiled or mixed with other rations. Utilization of water hyacinth as a fibre or in biogas production in East Africa requires that processing constraints be overcome and industrial capacities improved. Water hyacinth should be regarded as a weed foremost and an under-exploited resource secondly. Any attempts to better utilise water hyacinth must be within the context of attempts to destroy it.