Oat crown rust
Crown Rust, also known as leaf rust, is caused by a fungus,Puccinia coronata f.sp. avenae. The Crown Rust fungus is specific to cultivated oat, wild oat, and a few other wild grasses, but will not infect wheat, barley or rye.
Crown Rust reduces oat yield and causes thin kernels with low test weight - factors which greatly reduce milling quality. Loss due to disease can reach 100 per cent if infection is early, if it is a susceptible cultivar, and if weather conditions are favourable for the development of fungal spores and their spread.
Symptoms of Crown Rust include orange pustules of spores developing on oat leaves (see photos). Each pustule contains thousands of spores that can be spread to neighbouring plants and produce a new pustule in only seven to 10 days under ideal conditions.