“…All previous competition studies used traditional weed assessment methods based on sampling techniques, where C. arvense shoots were counted or biomass was harvested in small plots (1 m 2 ). Much work on the detection of C. arvense based on images from unmanned aerial vehicles (UAV) has been carried out (St ahl et al, 2013;Garcia-Ruiz et al, 2015;Olsen et al, 2017;Sørensen et al, 2017;Mink et al, 2018;Rasmussen et al, 2019;Forero et al, 2019) but methods to count overlapping C. arvense shoots are still lacking. As discussed in Rasmussen et al (2019), it is far from trivial to detect C. arvense automatically in cereals based on image analysis.…”