Leaf Rust is a term used to describe fungi that can attack ryegrass, primarily:
• Crown Rust (Puccinia coronata) also referred to as leaf rust
• Stem rust (Puccinia graminis)
Rust can severely hamper the growth of a ryegrass plant as well as reducing the plants nutritional quality (ME) and
palatability to livestock.
How to identify Ryegrass Leaf Rust
Crown (or Leaf) Rust appears initially as yellow dots on leaves, later developing into bright orange circular powdery spots or pustules up to 1mm in length on ryegrass plants. Rust tends to thrive in hot and humid weather. Rust also tends to attack pasture when there are high levels of herbage present. Weaker plants leaves as well as those that are moisture or nutrient stressed are most susceptible.
All ryegrass varieties can get leaf rust, however some such as Matrix are very resistant to leaf rust.
Pasture management such as applying nitrogen fertilizer and keeping pastures under control (avoiding them from getting too long or rank and limiting the build up of dead material at the base) of a pasture can limit the problem of leaf rust.
There are no viable chemical treatments for rust in grazed pasture situations.