I have about 10 red twig dogwood shrubs all around my house that were planted 5 years ago and up to last summer did beautifully. But this year, the majority of them have experienced major die-back (75% of branches appear to be dead) and 2 or 3 of them seem to have died entirely! The remaining shrubs have sparse leaves near the tops of the branches. Over the years, I have minimally pruned them, fed them some organic fertilizer and mulched with chopped leaves or hardwood mulch. What’s going on? It looks like I may lose a 20′ run of them alongside the eastern wall of my home.
It sounds to me like it might be twig blight (canker). This can be controlled through cultural practices: Carefully clean up dead leaves in the fall so that the disease cannot overwinter. When removing the diseased branches dispose of them rather than compost. Pruning twig dogwoods properly will make a difference in controlling twig blight. There are two methods for pruning twig dogwoods, Rejuvenation every 3 years or thinning by 1/3 every year, cutting out the oldest wood. Margaret follows the rejuvenation method. For more details and illustrations about both methods check out this CO State fact sheet, page 5 for thinning and pages 5 & 6 for rejuvenation. Regardless of which method you decide to adopt later, I would try a rejuvenation pruning now to see if you can save the shrubs. Since the fungus can travel on the blades of your pruners, make sure that you disinfect them between cuts!