The disease affects barley, rye, triticale and a number of grasses, particularly ryegrasses. There are specialised forms of the pathogen which are generally restricted in their host range.
The fungus causes scald-like lesions on leaves, leaf sheaths and ears. Early symptoms are generally oval lesions which are pale green. As the lesions age they acquire a dark brown margin, the centre of the lesion remaining pale green or pale brown. Lesions often coalesce forming large areas around which leaf yellowing is very common. Infection often occurs in the leaf axil which can cause chlorosis and eventual death of the rest of the leaf.
The fungus is seed-borne but the importance of this phase of the disease is not fully understood. The most important source of the disease is probably crop debris from previous crops and volunteers which become infected from the stubble from previous crops.
Autumn sown crops can become infected very soon after sowing. The disease spreads mainly by rainsplash although long-distance spread by air-borne spores is also possible.
The disease can be very severe, particularly in the south west and west of the UK where conditions are generally mild and wet. The most serious effect on yield in both winter and spring barley results from attacks that develop between first node detectable and boot swollen growth stages.