Loose smut
Ustilago nuda

The major symptom of loose smut is the "smutted" grain heads, which contain masses of black or brown spores where the grain would normally be. The spores completely replace the grain head so that there is no grain to be harvested on infected plants. It may be possible to identify infected plants in the field before they reach the flowering stage by looking for plants which are taller and more mature than the rest of the field. The fungus causes infected plants to grow slightly taller and mature slightly sooner than the uninfected plants in the field. Since it must infect through the open florets, this gives the fungus a competitive advantage by allowing it to fall down to the healthy plants and insuring that the fungus has a little extra time to produce and disperse spores before the florets of the healthy plants open.