Uromyces betae

Rust is caused by the fungus Uromyces betae. Despite its wide geographical distribution, its economic impact is often considered to be far less important than powdery mildew or Cercospora. This is mainly explained by the fact that it appears later in the season. In some regions (ex. along sea coasts) it can sometimes cause serious damage.

Development factors
Requires relatively cool temperature (between 15° and 22°C) for its development but will tolerate warmer temperatures as well. The key factor is moisture for long periods.

Small circular pustules, redorange to brown and often surrounded by a yellow halo appear on both sides of the leaves and produce a fine, orange powder.
LATER STAGE: Leaves dry up.