white powder encircling trunk of Birch sapling

[Polyethyl]

I recently planted a birch sapling to replace a birch tree that had to be felled after this winter's storms.

Someone has put a semicircle of white powder around its trunk. What on earth could the powder be?

Are you sure it is not mycelium? Some mushroom spores can leave a white powdery residue.

No. Definitely powder.