Covered smut disease in barley and oats

Covered smut disease in extremely rare in the UK. However, it is important to recognise the infection symptoms in barley and oats, because it can severely affect crops grown repeatedly from home-saved untreated seed.

The pathogens that cause covered smut are Ustilago hordei, in barley, and U. segetum (U. kolleri) in oats.

The disease is very rare in the UK.

When infected (and untreated) seeds are sown, pathogen spores germinate and infect the developing seedling.

Spores can also land on soil and infect seedlings but this soilborne phase is short-lived and not as important as seedbourne infection.

The fungus develops (without symptoms) with the growing point of the plant until it colonises the developing ear.

At ear emergence, the ears seem normal, but grains are covered in a thin membrane. If this is broken, it can be seen that the grains have been replaced by masses of black spores, held in place by an easily ruptured transparent membrane.

After ear emergence, some spores may be released (symptoms become similar to those of loose smut) and carried by wind to neighbouring plants.  

However, many are retained within their membranous envelope until the crop is harvested.

During the threshing process, spores are released and contaminate the surrounding seeds.

Spores remain dormant on the outside of the seed.

When present, the disease is usually found in crops grown repeatedly from home-saved, untreated seed. There is normally a total loss of grain from affected plants.