Septoria leaf blotch of Oats

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.
Infected stubble is the main source of carryover infection from one season to another. The sexual stage of the fungus occurs on infested stubble and produces ascospores which are spread moderate distances by wind. Oat stubbles in paddocks rotating from oat probably contribute most of the inoculum to nearby paddocks. In multiple cropped oats where stubble is not destroyed, ascospores land on the new crop in much larger quantities, resulting in the development of earlier and more severe outbreaks.
During the season, the fungus on diseased plants produces splash-borne pycnidio-spores which spread the disease onto new foliage during rain. These spores do not move between paddocks but may also be produced by infested stubble residues and contribute to the development of new disease in multiple cropped oats.