Silver Birch

I have a young silver birch tree and at the end of each leaf there is some black fungus and with ants on it. The leaves are curling up. Any ideas what's wrong. Thanks

 

Have you had a really close look at the 'fungus', if ants are there too it could most likely be that you've got an infestation of black aphids and the ants are milking them for the honeydew they excrete. It won't cause any permanent damage.

 

Many thanks for this. It makes the little tree look quite unsightly though, is it possible to get rid of the black aphids with some sort of spray do you think?