I planted a red Dogwood (Cornus Florida) this spring. It is now
extremely sad looking, with ugly yellowing leaves with dark blotches.
I planted another one (not very close) this spring that is doing just
fine. Other nearby plants look fine (butterfly bush "Black Knight",
forsythia).

Its possible that its gotten too much water -- we've had an extremely
wet spring and early summer. I see a few mushrooms growing in the
mulch near the base. That doesn't seem like a good thing. Is that
bad?

Assuming it is getting too much moisture, what can be done? I
thought I planted it in a spot that would drain well -- there's a
small slope -- but maybe not. Is moving it or replanting an option
at this point? Is there any other problem that it could be having?

Swyck