ECONOMICS OF BIOLOGICAL-CONTROL OF KARIBA WEED (SALVINIA-MOLESTA MITCHELL) AT TENGWE IN NORTH-WESTERN ZIMBABWE - A CASE-STUDY

We assessed the feasibility, practicability and economics of biologica l control of Kariba weed (Salvinia molesta) in Zimbabwe. The weed has become an important aquatic weed in inland water impoundments in Zimba bwe, and is detrimental to irrigation, both domestic livestock water s upply, fisheries and the environment in general. During 1992-95, attem pts were made to control Kariba weed using a biocontrol agent (Cyrtoba gous salviniae: Curculionidae) on two dams comprising 16 ha in Tengwe commercial farming area in northwest Zimbabwe. The effectiveness of bi ological control of Kariba weed was apparent within four months of rel ease of the weevil agent and 99% control of weed was obtained within t wo years. The benefit, cost ratio of biological control as compared to chemical control, was 1:10.6 over a four year period. This study show s the effectiveness, economic benefit and environmental sustainability of biological control of Kariba weed under Zimbabwean conditions.