Runner Bean Rust
This disease is not to be confused with the rust that can affect Broad beans!
Rust attacks are a result of resting spores that have remained dormant over winter in the soil and reappearing early in the growing season to cause infections on leaves.
Attacks are generally more frequent in warm damp summers.
The fungal attack is first seen as off white cup-shaped spots on the top surface of the leaves with corresponding white pustules appearing directly under these spots on the lower surface of the leaves.
Later in the season, black pustules appear on both surfaces of the leaves, and sometimes the bean pods.
Heavy infections can cause the leaves to die and fall off, and on some occasions affected plants may be appear stunted, and the yield is reduced.
The infections tend to start from the lower / older leaves on the plant/s.
There are no fungicides available to the amateur gardener to control this disease.
Limited control can be had by promptly removing and burning infected leaves to limit spore production.
At the end of the season clear away all plant debris, and avoid growing beans on that site for several years.
Do not save seed from rust-affected crops.