Ascochyta fabae (leaf and pod spot) infection in field beans can come from primary seed borne symptoms developing on first leaf growth.
Circular spots appear on the leaf surface, they are brownish grey with a darker coloured margin. The centre of the lesions there will be pin prick sized darker spots, these are the fruiting bodies which contain spores. The spores can be spread by rainsplash to other foliage.Heavy infection can affect the pods with darker sunken lesions, which can ultimately affect the seed quality.
Wet conditions in early spring can encourage development of the disease.
Seed should be tested form Ascochyta infection and whilst there is not statuary standard for using infected seed it is not advisable to use seed with more than 1% infection.
Certified seed should be tested, it may be advisable to ask your seed supplier for a test result to ensure that seed is within scope.
Seed treatments are an option and would help but not guarantee full control.
Some varieties offer good resistance against Ascochyta, they may get infection but in most cases it would not develop as much as in non resistant varieties. Clipper and Wizard in particular offer good resistance, generally other subsequent varieties from the same programme will also offer good resistance, check with your advisor.
Neighbouring fields with bean volunteer plants can also be a source of infection, removing crop debris will help reduce this possibility.