Stem rust (SR) occurs throughout NZ, caused by the fungus Puccinia graminis, mainly in warm, dry conditions in summer and autumn.
Ryegrass, tall fescue.
SR produces brick-red powdery spots (or pustules) on leaves and stems. These are often fringed by the papery remnants of the leaf epidermis.
The pustules produce brick-red spores that are carried by wind or rain to other plants. These germinate to produce new pustules
Prevention and management
Use resistant ryegrass where SR occurs. To avoid SR, graze pastures at the correct time; do not allow them to get too long. The application of N fertiliser may help prevent SR.
If rust is present, hard graze to remove infected pasture and apply N if possible. New growth should show little rust. Fungicides are uneconomic.
Stem rust on a ryegrass stem.