Invasives Blog

Weeds wreak havoc, day after day, year after year. They degrade agricultural land, deplete water resources and destroy crops, as well as being alternative hosts for crop pests. Yet, while weeds do cause damage to crop yields, a newly published study reveals that the vast majority of the costs are due to weeding.

A male farmer manually removing weeds. Image © CABI

A team of scientists from CABI centres in Africa and Europe conducted an in-depth literature review and online survey as part of the first comprehensive study on the annual cost of invasive alien species on Africa’s agricultural sector. The study estimates that annually invasive alien species cost Africa USD $65.58 billion, 55.4% of which can be attributed to the labour costs of weeding invasive alien species.

Smallholders are largely poor and food insecure and hand weeding is still the only weed control option open to most. This method of weed management is physically demanding and time consuming. The total cost of weeding invasive alien plants, which often comprise more than half of the weeds in arable fields, is huge. The CABI scientists put a monetary value on the weeding labour for the entire African continent. This was based on a review of existing literature, which revealed weeding in crop types can take 50-92 person days per hectare.

The knock-on effects of weeding

In talking about the burden of weeding on women and children, the paper highlights the hidden costs of weeding. Most African smallholdings are owned and operated by families and it is usually the women and children that undertake the labour-intensive task of weed removal.

The large estimate for the weeding costs may come as a surprise but this work is never measured as part of the African economy and is therefore not accounted for. In addition, it should not be concluded that people are being paid that amount as salaries. Rather, the estimate represents an opportunity cost, meaning if people didn’t need to weed invasive alien species they could do something else.

Thus, the knock-on effect of weeding invasive alien species in agricultural fields is that women have less time for child-care, community activities and income-generating work. For children, it can mean being removed from school during peak weeding season, negatively impacting their education. These unseen costs need to be acknowledged and addressed if rural farmers are to break the cycle of low productivity, poverty and food insecurity.

A female farmer working in a field. Image © CABI

Prioritising resources to tackle invasive alien species

The CABI research highlights the need to improve the outlook for smallholders in developing countries, who are resource-poor and susceptible to the consequences of invasive alien species. The results show that such species have a major impact on people’s livelihoods, particularly women and children whose work is often informal and who bear the brunt of unpaid work, such as weeding. The current study reveals the hidden costs of these species, which should convince decision makers of the need to prioritise resources to help control and manage invasive alien species.

The authors recommend that measures be implemented to prevent new species from arriving and established species from spreading. Moreover, management costs for widely present and impactful species should be reduced through methods such as biocontrol. This will potentially reduce future production costs and lower yield losses. At the same time, it may improve the livelihoods of farmers and other affected land users by giving them time to engage in economic activities that support development of the continent.

Additional information

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, ‘The economic cost of invasive alien species to African crop and livestock production,’ CABI Agriculture and Bioscience, 19 August 2021, DOI: 10.1186/s43170-021-00038-7

Correction: Invasive alien species may cost African agricultural sector $3.66 trillion per year

This paper is being corrected after the identification of two errors. The first error was in the calculation of weeding costs in which the wage costs of weeding per square kilometre were applied instead per hectare. The recalculation estimates the total cost of invasive alien species to the African agricultural sector as $65.58 billion per year not, as originally stated, $3.66 trillion. This is equivalent to 2.5% of the gross domestic product of all African countries combined, rather than the originally stated 150%. The second error was in the calculation of the crop loss due to Phthorimaea absoluta in which the value was not corrected for the abundance of this species within each country. The recalculation estimates that this species costs the agricultural sector $4.1 billion in crop losses per year, rather than the originally stated $11.4 billion. Further details can be found in the correction text.

You can read the full correction text and amended paper 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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