I don't like to be the bearer of bad news, but anthracnose is a serious disease that plagues dogwoods. Dogwoods have been particularly hard hit by the disease in the eastern United States. Symptoms of dogwood anthracnose include deformed flowers and small, circular spots on the leaves. Several other less harmful plant diseases resemble anthracnose, so contact your county extension service for information on how to properly diagnose the problem. Anthracnose is caused by a fungus that spreads quickly in warm, wet weather. Weakened trees and those suffering from drought, nutrient deficiency, or other diseases are most susceptible.
Keep a close eye on seemingly healthy plants in your landscape, watering and feeding them as necessary to prevent plant stress. Although dogwood tolerates shade, it grows best in partial shade; morning sun with afternoon shade is ideal. If yours is growing in a shady site, the foliage may remain wet for long periods after rain or dew, providing conditions favorable for development of the disease. Consider pruning out some surrounding growth to increase airflow and promote drying. The best control measure for your infected tree is to prune out the diseased twigs. Use a pair of sharp pruners and cut infected twigs several inches below the infected area. Sterilize the pruners in alcohol or dilute bleach between cuts to prevent spreading the disease. Gather and destroy cut twigs and fallen leaves. Fungicide sprays are most effective when applied early in the season, just before buds open.