The pathogen is the imperfect fungus Ramularia collo-cygni, which resides in plant tissues in an endophytic form for a long time, showing no signs until the flowering phase or the onset of stress. Typical symptoms include the appearance of small reddish-brown or brown-black rectangular spots, surrounded by a chlorotic halo, which are delimited by leaf veins.
As the disease progresses, the spots coalesce, causing premature yellowing and death of the leaves, while sporulation in the form of black dots can also affect awns and glumes. Visual diagnosis is difficult due to the similarity with physiological leaf spots, therefore PCR testing is used for accurate identification of the pathogen.
Currently, there is no generally accepted classification of races or pathotypes of Ramularia collo-cygni, although studies confirm the high variability of the pathogen. Specific resistance genes in barley breeding are not widely described, and resistant varieties are practically absent, making the search for resistance donors a priority task.