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  • on 24.08.2010
  • at 10:00 AM
  • by Staff

Africa: scientists use weevils to control water hyacinth 0

There is hope at last for more than 40 million people in Kenya, Uganda, Burundi and Tanzania who depend on Lake Victoria the world’s second largest fresh water lake and whose lives have been devastated by the water hyacinth which infested 12000 ha of the lake.

Two biological control agentsNeochetina and N. bruchi released after the water hyacinth in River Mono, Republic of Benin , in an effort to tackle the devastation caused by the water weed and free water ways for fishing and transport have proved successful”, reveal researchers at the International Institute of Tropical Agriculture (IITA), based in Ibadan, Nigeria.

According to Obinna Ajouno, a scientist with the IITA, the two biological agents, which are weevils, feed on only water hyacinth and have proved to be effective control agents of the water weed.

The released weevils were mass produced by the Department of Agriculture in Porto-Novo using start-up colony supplied by the IITA that also provided technical assistance.

Ajouno says the biocontrol exercise is the first of its kind by researchers in the Mono River to control the aquatic weed.

Previous efforts by IITA and partners using bio-control agents against the water hyacinth yielded success on the Oueme River eight years ago. So we are confident this approach will produce results,” he explains.

Participants in the release included the Department of Agriculture, the National Coordination Unit of the Benin Economic Community of West African States’ Water Weeds Project, the local communities and IITA.

The project is part of the ongoing African Development Bank (AfDB) funded Economic Community of West African States (ECOWAS) integrated project for the control of aquatic weeds involving physical removal, utilisation, and biological control methods. A native of South America and alien to Africa, the water hyacinth Eichhornia crassipes often grows as floating plants or mats, as islands of plants floating freely on the water, or mixed with other vegetation on river banks. It multiplies both by seed and vegetatively by use of stolons and is capable of doubling in biomass within 6-15 days under optimum conditions.

In the areas bordering Lake Victoria, the weed was first recorded in Lake Kyoga (Uganda) in May 1988. Within Lake Victoria, it was observed in the Ugandan sector in 1989 Tanzania, in 1989 and Kenya in 1990.

The weed forms thick mats over the infested water-bodies causing obstruction to economic development activities and impacting negatively on the indigenous aquatic biodiversity. Furthermore the weed affects the conditions of the water-body and life of the plants and animals in them.

Floating mats of the water hyacinth for example drastically curtail the penetration of light into the aquatic ecosystem thus inhabiting the growth of phytoplankton.

In nutrient-rich waters, such as in polluted ponds or lakes, it can grow so quickly that the surface covered by the mats doubles every four to seven days.

Initially efforts to control the water hyacinth in Lake Victoria during the early 1990s were of limited success and were primarily directed at manually removing and conducting public awareness exercises.

In the mid-late 1990s, management to combat water hyacinth increased with efforts such as the Lake Victoria Environmental Management Programme (LVEMP-1) and the US Agency for International Development (USAID) through development funding for coordination efforts by Clean Lakes, Inc. Martinez, CA, USA.

Control actions included bio-control using weevils, mechanical

control using large harvesting and chopping boats known as the swamp devils.

The aquatic weed poses serious socioeconomic and environmental problems to millions of people in riparian communities and is, therefore, an added constraint to development.

The weed obstructs electricity generation, irrigation, navigation, and fishing; increases water loss resulting from evapotranspiration; and facilitates proliferation of such diseases as bilharzia.

In Uganda, the weed has interfered with operations at the Owen Falls Dam hydroelectric scheme, resulting in power cuts that affected the country ’s industrial output.

In Sudan alone, a partial evaluation of socioeconomic costs of the water hyacinth, estimates that annual water loss from evapotranspiration over 300 km2 of canal would be enough to irrigate more than 400 ha.

Effects on navigation in the Nile include 50 per cent higher running and maintenance costs and 30 per cent more use of fuel. But the costs of bringing it under control have been prohibitive.

According to the International Development Research Centre (IDRC), the cost of chemical control alone over 15 years would have been in excess of US$19 million.

Until 2000, the Mono River which borders Togo was free of the water hyacinth. Researchers are of the view that the weed might have been infested through human activities.

Ajouno says the impact of these biological agents weevils  in the Mono River system in the years ahead will be monitored by regular field visits involving the collaborating institutions.

By Henry Neondo News from Africa

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Direttore Responsabile Giuseppe Frangi