barley smut
A disease of barley caused by the fungus Ustilago nuda.
barley smut: fungal disease that destroys the grain
Barley smut is a fungal infection that replaces the barley grain with black, sooty spore masses. The disease is caused by Ustilago nuda, a pathogen that infects the developing seed inside the flower. When mature, the affected head crumbles into a dark powder of millions of spores instead of yielding usable grain. This makes infected plants worthless for malting, brewing, feed, or seed production.
The infection occurs at flowering or just before, when spores land on the stigma (female flower part) and grow down into the developing ovary. The fungus remains dormant inside the seed coat and becomes active only when that seed germinates. This hidden dormancy makes smut particularly difficult to control: infected seed looks normal and passes through cleaning equipment undetected.
Loose smut and covered smut
Two forms of barley smut cause different damage patterns. Loose smut, caused by U. nuda, produces naked spore masses that disperse into the air at heading time and can spread to neighbouring crops. Covered smut, caused by U. hordei, keeps spores wrapped in a membrane that resembles the normal grain husk. Both reduce yield and contaminate harvested grain, though covered smut is easier to separate mechanically.Control relies on seed treatment with fungicides rather than field spraying. Hot water treatment of seed, historically common in malting barley production, kills the dormant fungus inside the seed coat without harming germination. Chemical seed dressings offer more reliable protection and are now standard practice. Resistance breeding has produced varieties with good smut tolerance, though no complete immunity exists.
The name smut comes from the sooty black appearance of the spore mass, which resembles soot or charcoal dust. In global grain trade, smut contamination is monitored and typically limited to less than 1 percent by weight in quality specifications. Severe smut infections can render a crop unsaleable and force reclassification from malting to feed-grade barley, with significant economic loss.