We notice that the dogwood is very mature. We are not really sure of your question. We did not see a lot of foliage in the photo. We see some lichen on the branch but this is not a reason for any decline. http://extension.umd.edu/hgic/lichens-trees-and-shrubs
All you can do is prune dead wood and keep the tree well watered during dry periods. Here is our dogwood publication for more information http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG12_IPM_Series_Dogw...