Eyespot, Sharp [Rhizoctonia cerealis]

Pest profile

About the pest

Hosts

The disease affects wheat, barley, oats, rye and triticale.

Symptoms & Diagnosis

Symptoms

Symptoms occur as sharply defined lesions on the outer leaf sheaths. Young lesions have a sharply defined dark margin and frequently have shredding of the epidermis within the lesion. Multiple lesions up the stem can be found up to 30cm from the stem base. Later in the season, lesions on the stem have a pale cream centre with a dark brown, sharply defined edge. Sharp eyespot lesions are often superficial, but severe sharp eyespot is not uncommon and can cause white-heads or lodging.

Life cycle

The fungus over-winters primarily as mycelium on infected stubble with volunteers and some grass weeds also acting as sources of inoculum. The fungus can produce sclerotia which may act as overwintering structures. Infection may occur at any time during the growing season, but the disease is favoured by temperatures of around 9°C. Acid, dry and sandy soils and early sowing favour the disease. Cool autumn or spring temperatures may result in early infection by the fungus which can lead to severe disease.

Remarks

Importance

Sharp eyespot is common in the UK although, nationally, it does not usually cause significant yield loss. However, individual crops may suffer significant losses, particularly if the disease is present with take-all. Severe sharp eyespot has been shown to reduce yield by up to 25% but this is very unusual. Annual losses in the UK on average are probably less than 0.5%.