Dogwood Tree borers and disease
To control the borer you can treat the tree with Bayer Advanced Tree and Shrub insect Control or similar insecticide that lists Borers on the label. Always read the label for the correct amount to apply and what insects the insecticide will control.
The disease problem is best controlled using sanitation. Clean up the fallen branches and leaves Remove any dead or dying branches branches back to healthy wood. The dead plant material is a source of spores that will reinfect the tree. Spray tree with a fungicide containing either Copper or Chlorothalonil about every 14 days May through the first half of June. Contact your local Cooperative Extension Service for additional information to protect all of your landscape plants.