The poor dogwood — perennially beset with problems. Dogwood borers and leaf spots have always been regulars. But then there's dogwood anthracnose, a deadly fungus that decimated many native flowering dogwoods (Cornus florida). Powdery mildew, an unsightly fungal infection, doesn't usually kill the tree but probably weakens it until another pest comes along and delivers the final blow.
To increase your chances of enjoying a healthy dogwood, choose a cultivar with disease resistance to both anthracnose and powdery mildew; developed by Rutgers, the Stellar series, including 'Stellar Pink', 'Constellation', 'Celestial' and 'Aurora', show some resistance against anthracnose and powdery mildew and a high degree of resistance against dogwood borer. 'Appalachian Spring' is extremely resistant to anthracnose.
In the meantime, however, a better option might be the Kousa dogwood (Cornus kousa), which has better resistance to anthracnose and moderate resistance to powdery mildew. Unlike C. florida, Kousa dogwood "flowers" after the leaves appear, so you don't get that fairyland burst of white that's so welcome on an early spring day. But getting a leg up over two devastating diseases is pretty nice too.