Uromyces viciae-fabae var. viciae-fabae is a typical example of a rust fungus that carries out its entire life cycle on one host, which, in the UK, is the broad bean. Unlike chocolate spot, the infected leaf tissues remain alive, providing nutrients for the fungus while it produces dusty brown airborne dispersal spores. A semi-dormant resting spore carries it over the winter.
Another fungal pathogen, Didymella fabae (syn. Ascochyta fabae), causes spots on leaves and pods, but is usually less damaging than broad bean rust.