Abstract:

Water hyacinth, Eichhornia crassipes (Liliales: Pontederiaceae) is a troublesome
aquatic weed of South American origin and is specifically a native of the Amazon
River basin in Brazil. It has been described as the world's worst aquatic weed
mainly because of its negative effects on the livelihood of man. It occurs widely
within the tropical and sub tropical regions that lie between 40°N and 45°S
(Holms et a/ 1977). Water hyacinth therefore is neither a new nor a unique
aquatic weed to Uganda as it occurs widely in Australia, Southern Africa, Indian
sub continent, West Africa, China, North America, South America, The Pacific
Islands and lately, the East African countries (Julien, 1999; Piertese, 1987).
Harley (1990), Woomer (1997) and Julien et at (1999) excellently review detailed
morphological and biological characteristics of the weed.
One thing common with areas water hyacinth has invaded is the negative
impacts on man' s livelihood. The weed impedes water transport, aids in spread
of deadly tropical diseases by offering ideal breeding grounds for malaria
carrying mosquitoes and biharzia carrying snails. Where it occurs, water
hyacinth commonly interferes with hydro — electricity and water supply by
blocking turbines and water in take points.
Water hyacinth is a difficult weed to control and therefore it is virtually
impossible to ERADICATE it. This is because the weed has complex survival
characteristics like the ability to double its biomass within a fortnight under
favourable conditions and it can produce seeds that sink and can remain viable
at the bottom of a water body for more than ten years. Any control attempts
therefore, should aim at reducing the weed biomass to a manageable level were
it ceases to impede activities related to water