Weed biological control in Zimbabwe: Challenges and future prospects

Abstract

In Zimbabwe, the structure and integrity of various ecosystems is rapidly deteriorating, in part due to invasive alien plants. While there is recognition of the challenges posed by invasive alien plants and the complexity surrounding their successful management, very little has been done, documented or evaluated in the country recently, including classical weed biological control activities. We review the current status of invasive alien plants and classical weed biological control in Zimbabwe especially their management and legislation governing this management. We record the presence and distribution of weed biological control agents currently in Zimbabwe. The Biological Control Target Selection (BCTS) system was used to identify invasive plant species in Zimbabwe that could benefit from on-going or new classical biological control programmes. While biological control has been implemented in the country since the 1960s, and significant control has been achieved on floating aquatic macrophytes, no biological agent has been released on a terrestrial weed since 1961. However, 10 agents released in neighbouring South Africa have spread naturally into the country on contiguous plant populations and some are providing gratuitous control of some of the weeds. We identified 19 invasive alien plants that could be successfully managed through classical weed biological control, and for 12 of these, this could be achieved at minimal cost, as agents are available within the region. Zimbabwe, perhaps with the help of international aid organisations investing in the region, could: a) conduct extensive surveys of established biological control agents already present in the country; b) redistribute these agents into areas of the country where they are not already present and foster those spreading north in South Africa and likely to arrive eventually through natural spread, and; c) initiate new weed biological control programmes against new targets by importing new agents available from South Africa or Australia.