The disease affects wheat, barley and grasses.
The disease is normally first seen as stunted areas of poor growth. Affected crops are frequently found on light land. Affected patches can be visible as early as December as sharply delineated but irregular areas of stunted growth although the crop remains a normal green colour. Roots and the soil adjacent to affected plants show characteristic white hyphal masses (like small pieces of cotton wool about 1mm across). Fruiting bodies (basidiocarps) like tiny mushrooms can sometimes be found within affected patches between January and March. They are approximately 2 cm high with a 1 cm diameter convex cap.
Little is known about the disease cycle although this is a soil-borne fungus which survives between susceptible hosts as sclerotia or as mycelium on root debris. It infects crops soon after emergence, colonises roots, produces sclerotia and then produces air-borne basidiospores. These spores may play a part in long distance spread of the disease. The role of the basidiospores is unclear.
Until recently, the fungus had not been recognised as a pathogen of cereals in the UK. It is now believed to be sporadic in nature, affecting a small number of crops each year, mainly winter barley. Winter wheat is less frequently affected than barley and losses each year will be very small in comparison with other diseases. Limited trials in winter barley suggest infection can reduce fertile tiller number by 40% and yields by 25-50%.