Collective action in the area-wide management of an invasive plant disease

Area-wide management (AWM) is a strategy for invasive plant pests and diseases in which management actions are coordinated across property boundaries to target the entire pest or pathogen population in an area. Because some people may benefit from the actions of others without bearing the costs, but group-level contributions are required to achieve effective control, AWM suffers from free-riding, yet it has rarely been studied as a collective action problem. To foster collective action for the management of huanglongbing (HLB), California citrus stakeholders have adopted two distinct institutional approaches: Psyllid Management Areas (PMAs), in which coordinated treatments are voluntary, and Pest Control Districts (PCDs), in which coordinated treatments are mandatory. Through a survey distributed to citrus stakeholders in Southern California and a regression analysis of participation levels in AWM over nine seasons, we assess the impact that individual perceptions, institutional approaches, and group-level determinants have had on collective action. Our results show that although citrus stakeholders are confident about the benefits of AWM, they are aware of collective action problems and identified the lack of participation as the main barrier to AWM. Group size, grove size, and heterogeneity in grove size were found to significantly impact collective action. In addition, our analysis shows that the two institutional approaches that were developed for AWM have followed a different trajectory over time, leading to a discussion of the determinants that may enable and sustain collective action for invasive species management.