Economics of biological control of Kariba weed (Salvinia molesta Mitchell) at Tengwe in north-western Zimbabwe- a case study

Abstract

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