Pests and pathogens in the cabbage-oilseed rape agroecosystem

The cabbage - oilseed rape agroecosystern consists of cruciferous crop plants with different levels of productivity and labour intensity. In Switzerland, such crop plants are cultivated mostly in small-scale agricultural settings. Cruciferous crop plants are hosts for a wide range of pest insects and plant pathogens. However, the importance of the damage caused by pests and pathogens varies according to the perceived value of the crop plants. The aim of the present study was to investigate the relationships within the cabbage - oilseed rape agroecosystem. Therefore, a production site analysis was conducted based on the abundance of the cabbage root fly and downey mildew. Flight activity and oviposition rates of the cabbage root fly were observed in cabbage and oilseed rape fields during the growing season. In addition, samples of cabbage and oilseed rape plants were analysed using molecular methods to detect possible infections with downey mildew. Results showed that fewer cabbage root flies were captured in cabbage fields compared with oilseed rape fields. In oilseed rape, main flight and oviposition activity of cabbage root flies were during the first and second generation. Furthermore, the downey mildew found on cabbage and oilseed rape belonged to the same population. These findings show that the cultivation of cabbage and oilseed rape in small-scale agricultural settings offers optimal conditions for pests and pathogens to spread and establish themselves.