I had one Willow die from this malady already. I have a second which
has now come down with the same problem. Namely, the bark at the bottom
of the trunk just comes off in hugh chunks about 1 or 2 feet long.

These trees are about 6-7 years old.

I'd hate to lose the second one, which is now about 25 feet in height.

Anyone have any idea as to what causes this?