The species of the pathogen are crop specific, mainly occurring on barley and oats.
There are no symptoms of the disease before ear emergence. At ear emergence the ears seem to be normal except that the grains appear to be covered in a thin membrane. If this is broken open it can be seen that the grains have been replaced by masses of black spores held in place by the transparent membrane. The membrane is relatively easily ruptured and as spores are released the symptoms become similar to those of loose smut.
After ear emergence some spores may be released on to the rest of the crop and carried by the wind to neighbouring plants (as in loose smut, caused by U. avenae and U. nuda). However, many are retained within their membranous envelope until the crop is harvested when, during the threshing process, they are released to contaminate the surrounding seeds. In either case, the spores remain dormant on the outside of the seed until it is sown when they germinate and infect the developing seedling. The fungus then develops with the growing point of the plant until it once again colonises the developing ear.
The disease is very rare in the UK and is usually only found in crops grown repeatedly from home saved, untreated seed.