These problems, diseases and pests are known to affect Bean plants:
Aphids : Also known as greenfly and blackfly, Aphids are a common sap-sucking garden pest.
Spider Mites : Tetranychus urticae (an animal with over 60 common names, including red spider mite and two-spotted spider mite) is one of many species of plant-feeding mites found in dry environments, and generally considered a pest. It is the most widely known member of the family Tetranychidae or Spider mites. [source http://en.wikibooks.org/wiki/Horticulture/Tetranychus_urticae]
Bean mosaic disease : Tend to cause plants to turn a yellow green and produce few or no pods.
Bacterial bean blight : Disease which causes bright yellow or brown spots on leaves.