Stem Disease on Red Tip Dogwood
This looks like Botryosphaeria Canker, a fungal disease on the stem. The pathogen can infect all ages of stem tissue through wounds, pruning cuts, and leaf scars. Heat, drought stress, and winter injury can increase disease incidence. Diseased wood is reddish brown in appearance.
All you can do is prune back to healthy tissue during dry weather. Make sure mulch is no thicker than several inches and away from base of stems. Keep well watered during dry periods. See our website for more information http://extension.umd.edu/hgic/botryosphaeria-canker-shrubs