What is wrong with my dogwood?
We looked at the photos. Dogwoods in general are suspectible to several fungal diseases such as powdery mildew and spot anthracnose. This has been common this year due to the cool wet spring.
You are most likely dealing with powdery mildew on your trees but in the right photo the leaves look like they are exhibiting symptoms of discula anthracnose, a more serious disease of dogwood. This disease was more common in the past and some varieties are more susceptible than others. See our page on this disease and management. All you can do is monitor the health of the trees. Rake up any fallen foliage, water during dry periods, and make sure mulch is no thicker than several inches. https://extension.umd.edu/hgic/topics/dogwood-anthracnose-discula-trees
There is a range of susceptibility among dogwood to powdery mildew. The best recommendation is to plant powdery mildew resistant varieties in the future. Pruning for air circulation may help. You will have to monitor the plant in the future and decide if you want to spray fungicides or horticultural oil products listed for powdery mildew. This disease does not kill the plant but can weaken it.
Here is more on care and management of disease of dogwood. Look for resistant varieties in the future.