Help........Flies!

I have a beautiful laburnum tree and the last few weeks its been turning black and is covered in swarms of flies. Anyone tell me what is attracting the flies and what I can do?

 

Hi there - is there any chance of picture Jenza. The flies sound like they are attracted to something but without seeing what your seeing, its difficult to know what is going on.

 

little black flies love yellow, but don't suppose it is flowering now, so can't be that.