Managing Cirsium arvense, Sonchus arvensis and Elymus repens in northern European arable farming – where are significant knowledge gaps?

Book of Abstracts p. 213: The perennial creeping weeds Cirsium arvense (L.) Scop., Sonchus arvensis L. and Elymus repens (L.) Gould cause large problems in agricultural production in northern Europe. The management of these species is difficult in organic farming, but easier in conventional farming using herbicides. We collected and analysed literature on the response of these weed species to management practices in order to find knowledge gaps. C. arvense and E. repens are more studied compared to S. arvensis. Both C. arvense and E. repens have recently been the subjects of extended reviews. Elymus repens, a rhizomatous grass, is vulnerable to disturbance and competition due to weak seasonal dormancy, shallow creeping rhizomes and short-lived and low-spreading seeds. Tillage and mowing can effectively control E. repens, but efficacy varies between clones, seasons and treatment frequencies. Combined effects of direct control and competition from main crop/subsidiary crop merit further research. Cirsium arvense and S. arvensis are dicot species with creeping roots, with C. arvense roots being situated deeper in the soil than S. arvensis and both having deeper roots than the rhizomes of E. repens. Cirsium arvense can sprout from the intact root system even below the plough layer. Spring tillage has been shown to control C. arvense better than autumn tillage, and horizontal root cutter (prototype) have promising results on this species. Sonchus arvensis sprouts mainly in spring and summer thus indicating seasonal dormancy. Therefore, spring tillage controls S. arvensis better than autumn tillage. The effect of competition from main crop and subsidiary crops needs further investigation. While E. repens and C. arvense can be significantly controlled by a simple mechanical control strategy alone (repeated tillage and deep root disturbance, respectively), S. arvensis must be managed by a combination of different non-chemical methods. Identified gaps focus on the deep root system and sexual reproduction (C. arvense), the link between disturbance, competition, withering and dormancy in roots (S. arvensis), and the long-term effect of different integrated weed management strategies on the population dynamics (E. repens). We conclude that more research on all three species is needed, especially on the less studied S. arvensis. Keywords: Couch grass, creeping thistle, perennial sow-thistle, mechanical control, crop competition, cover crop, subsidiary crop Acknowledgements: This research was part of the project “AC/DC-weeds- Applying and Combining Disturbance and Competition for an agro-ecological management of creeping perennial weeds” funded within the ERA-Net Cofund SusCrop/EU Horizon 2020, Grant no. 771134.