Crimson Frost Birch - losing leaves...blight? (growing, spring, planting)

[33458]

This particular hybrid is supposed to be resistant to blight, but I can't find anything else online that matches what seems to be happening...new Spring planting, growing very well since planted...now the beautiful mahogany leaves are turning scarlet and yellow and then dropping. Not all of them, and there is new growth that seems unaffected, but I'm worried - went from a fully covered, robust sapling to a sparse, possibly troubled little tree.

Any suggestions?

[wit-nit]

Here's a good question and answer site about birches...Questions On Birch