Covered smut of barley is caused by the fungus Ustilago segetum var. hordei (formerly U. hordei). This is a different fungus to that causing covered smut of wheat. This disease is generally well controlled because of the regular use of seed treatments.

What to Look For

Affected plants usually do not show symptoms until ear emergence. Infected ears typically emerge at the same time or slightly later than that of the healthy stems. Also, infected ears often emerge through the sheath below the flag leaf. All of the florets of infected ears are replaced by masses of dark brown to black spores. The spores of covered smut are held more tightly than those of loose smut.

Covered smut on barley (Grant Hollaway, Agriculture Victoria).

Disease Cycle

During harvest the spores of effected heads spread and contaminate healthy grain. At sowing the smut spores germinate at the same time as the seed and infect the germinating plant. Infection of seedlings is favoured by earlier sowing as the fungus prefers drier soils and temperatures of 15-21°C. The fungus grows systemically within the plant, usually without producing symptoms and then it replaces the young grain with its own spores.

Receival Standards

Grain Trade Australia’s commodity standards have a nil tolerance for bunt in all grades of barley. See the table in the introduction.

Control

Covered smut of barley can be effectively controlled by using fungicide seed treatments every year. Following infection new seed should be obtained from a clean source. Resistant varieties are available.