406 | wileyonlinelibrary.com/journal/wre Weed Research. 2020;60:406–414. © 2020 European Weed Research Society 1 | INTRODUCTION The term 'natural' in our biological world is considered becom- ing obsolete due to human influences (McNeely, 2001). Under the influence of humans in this epoch, organisms are becoming transported at an unprecedented rate between regions faster and further (Ricciardi, 2007; Ricciardi and Cohen, 2007) and have caused substantial changes to recipient ecosystems (Asner and Vitousek, 2005; Simberloff, 2011; Kenis et al., 2017). In some cases, the introduction of these species may result in economic benefits and/or the addition to indigenous nutrition (McNeely, 2001). For example, substantial amounts of human dietary needs worldwide are provided by species that have been introduced from elsewhere (Hoyt, 1992). In this context, therefore, species introduction is required and crucial for sustainable human welfare. In contrast, there is a myriad of introduced species that arrive in new environ- ments with devastating consequences (Blackburn et al., 2014). The impacts of these deleterious introduced species, albeit ecologi- cally serious, are not limited to ecosystems structure and function alone but may also affect human health and livelihoods in novel environments (Shackleton et al., 2019). The acclimatisation of such devastating new species in novel ranges—termed 'biological Received: 23 August 2019 | Accepted: 24 March 2020 DOI: 10.1111/wre.12439 ORIGINAL ARTICLE Weed or not a weed? Density, perceptions and management of Chromolaena odorata (Asteraceae) in West Africa: Voices from Ghana Pascal O. Aigbedion-Atalor 1,2,3 1 International Centre of Insect Physiology and Ecology, Nairobi, Kenya 2 African Regional Postgraduate Programme in Insect Science, University of Ghana, Legon, Ghana 3 Department of Zoology and Entomology, Centre for Biological Control, Rhodes University, Grahamstown, South Africa Correspondence Pascal O. Aigbedion-Atalor, International Centre of Insect Physiology and Ecology, P.O. Box 30772-00100, Nairobi, Kenya. Email: pascalatalor1@yahoo.com Funding information German Academic Exchange Services Subject Editor: David Clements Trinity Western University, Langley, Canada Abstract The status (weed or beneficial shrub) of Chromolaena odorata in West Africa has been a major subject of debate since its introduction in the 1930s. Its negative impacts on agriculture and biodiversity are clear. However, indigenous people have harnessed several benefits of the plant, making management strategies less straightforward. Using indigenous voices in Ghana, the current perceptions of C. odorata in West Africa were assessed. Here, 90 respondents in three regions of Ghana were inter- viewed, using questionnaires, on aspects relating to the abundance, perceptions and management of C. odorata in their communities. Overall, results showed that the den- sity of C. odorata had declined. The majority of the respondents considered C. odor- ata as a fallow shrub, a medicinal plant or both. However, impacts on crop production and injuries incurred during physical control were also highlighted. The local uses of the plant in Ghana included treating fevers and injuries, and as a fallow shrub for soil nutrient replenishment. Although most of the respondents classified C. odorata as a useful shrub in Ghana, they also highlighted the use of local farming tools such as cutlasses for the slash of the plant. The use of herbicides for the control of C. odorata was rare and not applied specifically for C. odorata. In conclusion, local awareness programmes on the deleterious impacts of C. odorata on ecosystem functioning and livelihoods are required for its effective management in West Africa. KEYWORDS abundance, conflict species, indigenous voices, invasive plant, Western Africa