Some varieties may differ in susceptibility. Loose Smut Smut diseases are caused by fungi that live as parasites on the host plant and produce soot-like spores in grains or ears. Smut fungi may be borne either on the inside or outside of the seed. On barley and rye, loose smut is caused by the fungus Ustilago tritici. Triticale is thought to be resistant to loose smut.
Infected seed appear normal.
However, when it germinates, the fungus becomes active and grows slowly in the growing point of the plant. Diseased plants appear normal until heading but may be taller and mature earlier than surrounding healthy plants. The fungus then grows rapidly and forms a compact spore mass to replace the cereal head. The black powdery spores blow away to leave a bare stalk. The spores are released as the rest of the crop is flowering, and they infect the developing grains of healthy heads, remaining dormant in the grain until that seed is sown the next season.