Snow mould is mainly a disease of winter barley, although other winter cereals are also occasionally affected.
Symptoms are typically seen after snow melts in the spring. Infected plants often have an extensive covering of white mycelium which spreads on overlapping leaves, causing a matting of leaf tissue. Later, as spores are produced on the mycelial mats, the affected patches assume a pink colouration. The fungus often infects the oldest leaves directly from the soil but eventually the whole plant can be affected. Plants die-off in patches, but good growing conditions in the spring can allow crop recovery where plants have survived infection. In years with prolonged snow cover, the disease can be severe. Large areas of the crop may be killed and re-drilling with spring barley may then be necessary.
Winter-sown crops become infected during the winter months, often under snow cover. The lower leaves of plants touching the soil surface become infected by hyphae growing from perithecia or directly from plant debris in the soil. Affected plants or dead plant material carrying perithecia or mycelial growth are returned to the soil after harvest. Infected seed may also contribute to initial infection of seedlings in the autumn. Spring sown crops are rarely affected.
Snow mould is commonly recorded but, except in isolated cases, damage is rarely severe. The disease is generally more damaging in parts of Scotland where snow cover is more common.