True loose smut of barley is caused by the fungus Ustilago tritici . The disease cycle is exactly the same as that of loose smut of wheat.
Infection occurs when the flowers develop.
The seeds become infected internally and must be treated with a systemic fungicide to eliminate the pathogen. Semiloose smut is caused by the fungus, Ustilago avenae . The disease typically causes small losses due to the use of resistant cultivars and fungicide seed treatment. It is most common when soil temperatures are cool and the soil is dry. Distinguishing semi-loose smut from true loose smut in the field is extremely difficult.