Moving perceptions on potato late blight control : Workshops with model-based scenarios

Late blight caused by Phytophthora infestans is one of the main diseases in potato production. The Netherlands has a high potato density and favourable weather conditions for the disease, and this combination leads to frequent outbreaks of late blight. A spatially explicit agent-based model of the host-pathogen system was used in workshops with conventional and organic farmers to demonstrate and discuss the potential role of resistant varieties for effective and sustainable control of late blight. We presented model-based scenarios and used qualitative and quantitative measures to analyse the effect of the workshop on farmers' perception on late blight control. The scenarios simulated effects of farmer decisions regarding the use of crop resistance and fungicide application on disease control at the landscape level over a period of ten years. The model showed that growing a resistant variety (with a single resistance gene) can reduce disease incidence in the landscape, however, after a couple of years resistance breakdown occurs by emergence of a new virulent P. infestans strain. If no countermeasures were taken the new virulent population could spread fast through the landscape, reducing potato yield of resistant fields. The model showed a number of resistance management strategies that could be effective to increase resistance durability. Differences in farmer perception were observed before and after the workshop as well as between conventional and organic farmers. By analysing the disease dynamics at the landscape level, the model showed the importance of collective action. To prevent emergence and spread of a virulent strain it is important to keep disease pressure low. To achieve this, all farmers have to cooperate. During the workshops farmers exchanged views and negotiated possible solutions. We conclude that the use of model-based scenarios in workshops was very useful to increase farmers' knowledge of the system and served as a good starting point for discussions among actors facing the complex problems of late blight control and potato resistance management.