Dogwood plant disease
The leaves in the photos show powdery mildew, a fungal disease. Older infected leaves can develop purple blotches that progress to dead areas. See our publication on management and control. The best recommendation is to plant powdery mildew resistant varieties in the future. Pruning for air circulation may help. You will have to monitor the plant in the future and decide if you want to spray fungicides or horticultural oil products listed for powdery mildew. This disease does not kill the plant but can weaken it. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG12_IPM_Series_Dogw...