Halo Blight of Oats Pseudomonas syringae pv. coronafaciens
Light green, water soaked spots, up to 1 cm diameter, appear initially and enlarge to oval spots with a yellow centre and a yellow green halo. As the disease progresses, the spots merge into brown irregularly shaped blotches. The leaves may wither and die, starting from the tip.
Survives on crop residues and seed.
Spread by raindrop splash, direct contact and aphids or other insects.