Laburnum tree

Merrycarol

We a a Laburnum tree in the garden which is about 30 years old, it is flowering beautifully but is also growing a green moss-like fungi on the branches which then die.  It has never been fed, all we do is prune it annually.  Any ideas on this problem?

nutcutlet

A photo would help

I have lichen all over one of my laburnums but it doesn't kill the branches.