Leaf rust
Oat leaf rust is also known as crown rust. The word 'crown' refers to the shape of a type of spore produced by this fungus and is not related to the disease symptoms. The disease is caused by the fungus Puccinia coronata var. avenae. The characteristic symptom is the development of round to oblong, orange to yellow pustules, primarily on leaves (Figure 7) but also on stems and heads. The powdery spore masses in the pustules are readily dislodged. The pustule areas turn black with age.
Figure 7 Leaf rust (Puccinia coronata var. avenae) may first appear in crops as 'hot spots' from an initial infection. Hot spots in early spring allow leaf rusts to build up to very severe levels by the end of the season
Figure 7 Close up of leaf rust on leaves
Oat leaf rust is potentially a very damaging disease, reducing both grain and forage yields. It does not infect wheat and wheat leaf rust does not infect oats. The fungus is carried over on volunteer oats and wild oats from season to season.
Control
Control is similar for stem rust (above). Foliar fungicide registrations exist for control of this disease, refer to Registered foliar fungicides for cereals in WA. When oats are grown for high quality or export hay, early cutting should be considered before the disease builds up and causes obvious damage to leaves (Figure 8).
Figure 8 Clouds of leaf rust spores were released when this infected hay crop was cut. The early harvest prevented further damage to leaves.