I have the same...I assume, but don't know, that it's powdery mildew from the wet weather and wind we've had.

My organic approach is to ignore it...and hope it goes away, since it's a native dogwood seeded from a stand within 20 miles from where it is now. My assumption being, it should withstand threats and weather here.

Dogwood anthracnose possibly. If so, the effects can vary from cosmetic to branch death or worse & there's nothing you can do. It is encouraged by cool, wet weather.

Looks like your dogwood has both....powdery mildew and what looks like the beginning of anthracnose.....As the previous posters have indicated.....

Thanks everybody. I will contact the extension service here to see if they recommend using a fungicide now or have other suggestions.

Too late for fungicide. That sort of stuff is to protect new growth.
Nothing will fix, or get rid of, the mildew that's already there.