The fungus infects leaves, sheaths and stems and may also infect heads. Symptoms begin as mottled light and dark brown blotches, with dark brown centres. They are restricted and distinct at first but may enlarge to cover most of the leaf. Lesions in the leaf sheath extend into the stem causing death and blackening which may lead to lodging. The fungus sometimes causes a dark discolouration of the grain when unseasonably late rain occurs. Septoria avenae blotch may cause up to 50% yield loss and crop lodging in extreme cases but losses of around 10% are more common in high rainfall areas. Tall or slow maturing oats are less likely to be affected by the disease than short (dwarf) or fast maturing varieties.
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