Module 4 - water hyacinth

Water Hyacinth (Eichornia crassipes): Recognising Water Hyacinth

Water Hyacinth is the world’s worst invasive water weed!
It is a floating water plant that grows about 20 cm high and has beautiful lilac blue flowers with yellow markings.
The leaf stalks have air sacs that enable the plant to float, and the long feathery roots hang down into the water.
It forms dense mats in lakes, rivers and wetlands. It does not tolerate brackish water, so is found in the upper parts of estuaries rather than near the estuary mouth.

Water Hyacinth (Eichornia crassipes): From introduction to invasion:

Water Hyacinth comes from tropical South America, where it grows in rivers and lakes in the Amazon basin.
It was brought to South Africa as a decorative water plant because of its beautiful flowers.
It is an aggressive invader especially in water bodies with high levels of nutrients.
Water Hyacinth is a successful invader because:
- It can reproduce both vegetatively and sexually
- it grows faster than any other flowering plant in the world!
- Once a seed germinates, the plant grows very quickly and can flower within three or four months.
Water Hyacinth threatens biodiversity by:
- changing the ecosystem so that it no longer suits indigenous plants and animals
- forming thick mats that stop light getting into the water, so that underwater plants cannot grow
- removing oxygen from the water when the plants die, sink to the bottom and rot; this causes fish and other animals to move away.
Water Hyacinth is a problem for people because:
- it blocks waterways and interferes with transport, irrigation, fishing and recreation
- it worsens flooding and can even cause bridges to collapse
- disease-carrying mosquitoes can breed amongst the plants.

Some people use Water Hyacinth as a source of fibre for making rope, baskets and paper, fodder for livestock, compost, and to remove excess nutrients from water.

Water Hyacinth (Eichornia crassipes): Controlling Water Hyacinth:

Neochetina
eichhorniae

Niphograpta
albiguttalis

Removing Water hyacinth from a Cape town stream

To control Water Hyacinth it is important both to reduce nutrients (e.g. fertilizer, sewage) entering water courses, as well as to remove the invasive weeds.
Small amounts of Water Hyacinth can be removed by hand or by specially designed harvesting machines.
It is not a good idea to use herbicide as this can poison other plants and is dangerous for people and wildlife. When large amounts of Water Hyacinth are killed and start to rot, this removes oxygen from the water, which can kill fish and other water creatures.
Two biological control agents have been introduced to control populations of Water Hyacinth,
- a weevil (Neochetina eichhorniae) and
- a moth (Niphograpta albiguttalis).

Water Hyacinth (Eichornia crassipes)