Hi Audrey,
to NGA
I see a couple things:
- Some sort of insect infestation? Maybe Mealy Bugs. Causing a mildew/fungal problem.
- Not enough water. Dogwoods always (when you find them out in the forest) are growing in a moist place. By a stream or ...
The red crispy edged leaves would suggest to me that your tree isn't getting the moisture it needs. I would look for insects (What am I looking at in #3?) also. If you find insects (for instance Mealy Bugs), that could be the source of what looks like a fungus.
