Posted: 13/05/2016 at 07:47
There are a number of diseases which could be infecting your hawthorns and top of the list would be Juniper rust which also affects pears although damage is usually seen later in the year. Do you have any junipers or cedar trees nearby? Hawthorn cannot infect other hawthorns with this, the host is juniper.
Others possibilities are powdery mildew and hawthorn red fold gall. Google those to see if any images look similar.