Posted: 15/05/2014 at 12:55
I found this from DoveFromAbove from a previous entry
Sounds like Chocolate Spot - very common on broad beans especially in cool damp summers but doesn't usually affect the eating quality of the beans and doesn't infect any other plants. I wouldn't worry about adding the haulms to the compost - allotmenteers I know have been doing it for years with no noticeable ill effect.
It is said that it may help to avoid Chocolate Spot if you can plant your beans a bit further apart to allow good ventilation - and of course this is try of other fungal diseases too.