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Causal organism - Pyrenophora tritici-repentis
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Tan Spot survives mainly as dormant mycelium on stubble and crop debris. This produces pseudothecia on stubble which produce ascospores for long distance spread. In the absence of crop debris, initial infections in the autumn or spring may result from seed borne infection but this is not thought to be a major source of inoculum. Under warm, wet conditions, leaf spots produce dark conidia which are spread up the plant under wet conditions. The disease can infect the ear and cause discoloration of the glumes and the grain. Symptoms on the head are indistinct but can cause brownish glumes. Infected grains can have a reddish appearance, similar to fusarium infection. The disease develops over a wide range of temperatures but has quite a high optimum (20-28oC) and is favoured by long periods (18 hours or more) of dew or rain.
Importance
Tan spot is generally rare in the UK. Although it is occasionally recorded in disease surveys it rarely causes serious losses. In recent years the disease has been found causing serious losses on individual crops grown under minimum tillage systems.
