Thia old recipe is effective against blackfly on, for example, broad beans and runner beans but not against cherry blackfly.
The bracken must be gathered when brown and brittle dry. Pulp the leaves and store in paper bags until wanted.
Using a measuring jar, measure out 120cc (4fl oz) of the bracken and pour on 420cc (14fl oz) of hot water, stir and allow to soak for twenty-four hours, strain, then bottle into airtight jars and keep out of reach of children, of course.
For use as a spray, dilute 25cc (1 fl oz) to 4.5 litres (1 gal) of rainwater and spray each day for three days.