Centaurea cyanus
"Centaurea cyanus" is considered a noxious weed in arable crops, especially cereals and rapeseed. In winter wheat, one plant per m2 can cause a yield loss of up to 30 kg / ha. "Centaurea cyanus" produces around 800 seed per plant, which are either shed shortly before the harvest of cereals, or they are threshed together with the cereal grains, contributing to the further spread of the species by the harvesting machinery and contaminated seed. The occurrence of "Centaurea cyanus" strongly decreased during the last decades due to improved seed cleaning, more intensive nitrogen fertilization and herbicide use. However, "Centaurea cyanus" has become more common in cropland due to an increase in crop rotations dominated by winter cereals and rapeseed and the use of more selective herbicides with a low effectiveness against "Centaurea cyanus". In addition, the emergence of resistance against the herbicide class of sulfonylureas has been reported recently. Due to its strong roots, "Centaurea cyanus" is difficult to control mechanically in spring.