A participatory approach to design spatial scenarios of cropping systems and assess their effects on phoma stem canker management at a regional scale

• We combined participatory workshops and an available model for a scenario study.
• Stakeholder trust in the model required a dialogue on disease-practices interactions.
• Stakeholders designed context-dependent predictive and exploratory scenarios.
• Model-based scenario evaluation provided information on management options.
• The tested method could help the use of existing models for local management issues.

Phoma stem canker is a worldwide disease of oilseed rape, responsible for major economic losses. The main control methods are the use of resistant cultivars, cropping practices and spatial territory organization, involving large-scale spatial processes. A participatory approach can be useful for dealing with this problem, which requires stakeholders' coordination as regards to the timing and spatial layout of cropping practices. The scenario concept is used to plan possible future cropping systems and to reveal their main drivers. In this paper, we test a method to build quantitative land use scenarios and to test them with an existing spatially-explicit model to assess the effects of various scenarios on phoma stem canker management. It was built from previous participatory methods. The method we tested is composed of six steps: stakeholder identification, building with them a common vision of the disease behaviour, collective scenario design, and discussion with stakeholders of model-based scenario evaluations. We tested this method on a regional case study application in France. This application revealed benefits of the method with respect to the diversity of the designed scenarios (predictive and exploratory scenarios; driven by local or global context change) and the diversity of results on phoma stem canker management. Based on this application, recommendations for participation improvement and model acceptance are made: (1) build a partnership with a key local stakeholder; (2) describe and discuss precisely model functioning with stakeholders (avoid the “black box”); and (3) facilitate interpretation of scenario assessment by adapting model outputs. This method, combining a participatory approach (qualitative and quantitative construction of scenarios and their evaluation with an existing model) highlights the potential benefits of involving stakeholders in attempting to solve a local problem, in this case, phoma stem canker management.