Answer: Early foliage drop is a coping mechanism for drought stress. It is not so unusual for dogwoods to drop some foliage in late summer during an extremely stressful time. With mature established trees that have withstood the weather changes over decades, I would be very patient and wait and see until next spring.
In the meantime, you could do a slow, deep watering to hydrate them. Dogwoods are shallow rooted but their roots spread wide, beyond the tips of the branches. If you can slowly water over a wide area, letting it soak down in deep, that might be helpful. After watering, wait a few hours and then dig down to see how far the water went -- it should soak down ten inches or so to do the job.
Q&A Library Searching Tips