Crown rust (CR) occurs throughout NZ, but is found mainly in the North Island. It is caused by the fungus Puccinia coronata, mainly in warm, moist conditions from early summer to late autumn. CR depresses pasture growth and palatibility.
Ryegrass, tall fescue.
CR produces bright orange powdery spots (or pustules) on leaves.
The pustules produce orange spores that are carried by wind or rain to other leaves. These germinate to produce new pustules.
Prevention and management
Use more resistant cultivars where CR occurs.
To avoid rust, graze pastures at the correct time; don’t let them get too long. Application of N fertiliser helps prevent rust. If rust is present, hard graze to remove infected pasture and apply N if possible. New growth should show little rust. Fungicides are uneconomic.
Crown rust on ryegrass leaf