We have two Dogwood trees that have been in the ground about 5 years. This year they produced buds but nothing bloomed and no leaves appeared. The wood and branches are flexible and still green. We have noticed small little holes in the trunk and the branches of the trees. These small little holes have a black powder coming out of them. Upon shaving back a branch where one of the holes were we found a bunch of little creamy white eggs. I am not sure if this is the Dogwood borer or not. If so, are my trees too far gone to save? I have a third dogwood tree nearby that did produce flowers and leaves; however, it is starting to have the same little holes in it. What can be done to save it and possibly the other two trees?
I would agree that from this image and your description you are dealing with Dogwood Borer.
I would began treatment with a insecticidal spray, and you are at the perfect time to spray, spraying in May is recommended.
Here are some links with more information