About the authors - Natural resources management Invasive_floating_water_weeds_sp_ipm_3

Ajuonu, O

Tamo, M

Neuenschwander, P Beed, F

Toko, M

Hounkpe, C

About the authors

The authors are specialists in

different disciplines of

biological control. Obinna

Ajuonu, Manuele Tamò,

Peter Neuenschwander, and

Muaka Toko are stationed at

IITA-Bénin, Fen Beed at

IITA-Uganda, Catherine

Hounkpe is the Coordinator

of the Bénin ECOWAS

project, Integrated

Management of Invasive

Aquatic Weeds (IMIAW).

Present control initiatives across the West African Region

Many of the water bodies within the Economic Community of West African States (ECOWAS) are interconnected. Consequently,

water weeds spread regardless of political boundaries with one or more species present in the same water body. A management

strategy involving the countries that share the affected water basins therefore became necessary. The ECOWAS regional project

for the control of aquatic weeds, with funds from AfDB, provides the platform for these new collective efforts. It stipulates active

participation of the riparian population, researchers, and extension workers. Countries covered are Bénin, The Gambia, Ghana,

Mali, Mauritania, Nigeria, Niger, and Senegal. Water hyacinth, water lettuce, and the less prevailing water fern are the main targets

as well as some indigenous species such as Typha spp.

Integrated pest management (IPM), depending on biological control, but with physical removal of the weeds in specific locations,

and the utilisation of the weeds for composting, is the method of control adopted by the project. Progress has been made in some

countries. In Bénin, physical removal and utilisation of water hyacinth is being carried out in Nikouekondji village in Grand-Popo,

along the Mono river system. A similar approach is taken in Dangbo community along the Ouémé and Sô river system. The

compost manure from physical removal in the communities is used in vegetable production. In Senegal, following the successful

biological control of water lettuce and water fern, the focus is now on Typha spp. In the other countries, similar efforts are being

made.

Due to its experience in biological control of weeds, IITA has been contracted as a key partner in this regional project to empower

communities through capacity building and the supply of starter cultures of biological control agents for the implementation of

participatory and cost effective integrated control of floating water weeds.

Bénin received starter cultures of Neochetina eichhorniae from IITA in December 2009, while Ghana, Niger, and The Gambia have

made requests. In Bénin, the mass production of the agents and the field releases will be executed by the Plant Protection

Services and Department of Agriculture with technical assistance from IITA. The agents that will be released in the Mono River

system, which until 1993 had been free of water hyacinth, will likely spread to the neighboring Togo. In The Gambia, the presence

of water hyacinth in the Gambia River represents a risk of invasion into neighboring Senegal. - This highlights the need to urgently

implement biological control of water hyacinth in The Gambia.

By bringing together several countries, the ongoing ECOWAS regional integrated control of invasive water weeds is a boost to the

past initiatives by single countries. Through active participation of the concerned stakeholders and networking of countries sharing

common water bodies, sustainable management of invasive aquatic weeds based mainly on biological control methods can be

achieved across the region.

Slow but remarkable results

Reduction in weed cover due to biological control can take several years and will vary according to the weed species, climate,

aquatic ecology, and location. In Bénin, about 90% decline in surface cover by water hyacinth was achieved at Tévèdji, a fresh

water body, in a period of 8 years (Ajuonu et al., 2003). Biological control of water hyacinth in Bénin is estimated to have brought

returns of US$260 million, calculated (with depreciation) over a 20-year period (De Groote et al., 2003). For water lettuce, the

surface covers of two water bodies, both in Bénin, were reduced by 75-80% at Sè, and 35-80% at Adjaha, respectively , within five

years (Ajuonu and Neuenschwander, 2003), and about 90% in Senegal in one year (Diop and Hill, 2009a). In the case of water

fern, 75% reduction was achieved in 2-3 years in the Congo (Mbati and Neuenschwander, 2005), and 95% in one year in Senegal

(Diop and Hill, 2009b).

Left: Water lettuce in a lake

without biological control

agents. – O. Ajuonu

Right: Water lettuce in a lake

damaged by biological control

agent N. affinis. – P.

Neuenschwander

email: [email protected]