If the runner beans are flowering well but there is little or no crop, the cause could be lack of pollinating insects or dryness of the roots. So ensure that the site is sheltered enough to encourage insects and that the roots are watered enough at budding time.
This fatal disease of runner beans is characterised by a brown spots surrounded by a yellow halo on the leaves of the bean plants - eventually the leaf withers and dies.
This disease results as a problems in the seed that is sown and is caused by the Pseumonas phaseolicola bacteria. Try to avoid planting any seeds which are damaged, wrinkled or don't look quite right.
The only way to get rid of this disease is to burn the affected plants - do not save any seed from them.
A fungus that causes plants to rot at ground level; this may occur if runner beans have been planted too often on the same site. Water with a Chestnut compound and move to a fresh site next year.
These slimy pests will attack when the plants are first coming up.
Apply some slug pellets along the rows of beans or try and catch them using citrus traps.
Spray with an insecticide when you notice the aphids appear on the underside of leaves.
If the pods are nearly ready then use a safe insecticide such as malathion.