Invasives Blog

Invasive Alien Species have major economic, societal and ecological impacts. Until now, these costs have not been calculated for the African continent. A new study reveals the extent and scale of this economic burden on the agricultural sector in one of the least studied continents.

The study estimates the annual cost to African agriculture at USD3.66 trillion. This cost is primarily attributed to time spent weeding, yield losses caused by key pests and livestock income losses caused by alien weeds growing in grazing land.

The average annual cost of IAS per country is USD $76.32 billion, but there are large differences between countries. This is mainly because of differences in the type of pests present, the amount of agricultural land and the types of crops grown, as well as average agricultural labour wages in each country.

The map shows the estimated costs of invasive alien species for each African country. The colours of the countries reflect total estimated costs and the presented numbers are the estimated annual costs in million USD. A dash means no estimate was made (for example because that pest has not been recorded) and a zero indicates a very small estimate

The scientists estimated the economic impact of invasive alien species for a set area (e.g. one km2) based on data from the literature and survey results. Data for the African continent are sparse, with more data available for some countries than others. The scientists supplemented the data with information gathered through an online questionnaire. They then extrapolated the estimate to every country affected by the invasive alien species based on similarities between agro-ecological zones, crop value and the recorded presence of the species.

Yield loss estimates were possible for key species, such as Fall armyworm and Tuta (Phthorimaea) absoluta. It is probable that most costs are due to a few, highly damaging species. Therefore, it was decided to focus on species that were likely to have the largest impact on crop yields and for which sufficient data were available.

The cost of weeding for a particular country is based on the area under agriculture, the average time spent weeding and the average salary for agricultural labour. The area under crop was taken from a dataset using satellite imagery, taking into account multiple cropping seasons, where applicable. Data on the time spent weeding an area and the percentage of alien weeds were taken from literature from across the continent.

The estimated cost of weeding invasive alien species is an opportunity cost, meaning that if people didn’t need to weed invasive alien species could do something else, such as going to school or undertaking an income generating activity. The latter is especially important as most smallholder farmers rely on manual weeding methods.

These results highlight the need for measures that prevent new species from arriving and established species from spreading, and that reduce management costs for widely present and impactful species through methods such as biocontrol. This will potentially reduce future production costs, lower yield losses and improve the livelihoods of farmers and other affected land users.

Full paper reference

René Eschen, Tim Beale, J. Miguel Bonnin, Kate L. Constantine, Solomon Duah, Elizabeth A. Finch, Fernadis Makale, Winnie Nunda, Adewale Ogunmodede, Corin F. Pratt, Emma Thompson, Frances Williams, Arne Witt, Bryony Taylor, ‘Towards estimating the economic cost of invasive alien species to African crop and livestock production,’ CABI Agriculture and Bioscience, 20 May 2021, DOI: 10.1186/s43170-021-00038-7

The full paper can be viewed here:

Funding acknowledgement

The research was financially supported by the Foreign, Commonwealth & Development Office (FCDO), UK, and the Directorate‐General for International Cooperation (DGIS), Netherlands, through CABI’s Action on Invasives programme. CABI is an international intergovernmental organisation, and we gratefully acknowledge the core financial support from our member countries (and lead agencies) including the United Kingdom (Foreign, Commonwealth & Development Office), China (Chinese Ministry of Agriculture and Rural Affairs), Australia (Australian Centre for International Agricultural Research), Canada (Agriculture and Agri-Food Canada), Netherlands (Directorate-General for International Cooperation), and Switzerland (Swiss Agency for Development and Cooperation). See  for full details.

Other relevant research

This research builds upon previous CABI evidence notes on the impacts of invasive alien species including:

Tuta Absoluta Evidence Note 2019

Parthenium Evidence Note 2019

Fall Armyworm Evidence Note 2017


CABI works with farming communities around the world, supporting them as they battle with poor soil, invasive species, and pests and diseases, to improve their livelihoods and help provide food for an ever-growing population. Discover more about CABI’s projects that are tackling the problem of Invasive Alien Species

Action on Invasives

CABI’s global Action on Invasives programme aims to protect and improve the livelihoods of rural communities through an environmentally sustainable, regional, and cross-sectoral approach to managing invasive species. Find out more

Woody Weeds

CABI is working to mitigate the impact of woody weeds in East Africa by generating and sharing knowledge on their effects and finding ways that they can be controlled. Find out more

Addressing Scale Insect Threats in Kenya

In Kenya, scale insect pests are damaging native trees and crops and consequently, causing yield losses of up-to 91%. CABI is creating information packages for stakeholders on identification and management of scale insects that will improve practices and increase responses to pest invasions.  Find out more

Control of Fall Armyworm in East Africa

With partners, CABI developed an emergency response strategy that empowered local communities of six target countries to effectively manage and monitor outbreaks of Fall Armyworm in their respective localities, helping to prevent further spread. Find out more

Further information on all CABI projects can be found here

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