Birch tree leaves turning yellow and falling
 

We have 3 white birch trees in front of our house. They are about 50 years
old.

Now, in the first part of June, the leaves on 2 of them are turning yellow
and falling. They do not turn brown as they do in the fall. The fallen
leaves seem to have no problems on them other than they're yellow.

Any thoughts?

Thanks

Don in California