- In the past, anthracnose (Discula) was the most serious disease of dogwoods in the landscape and our forests but it is now less common. It causes the dieback or even death of infected trees. Powdery mildew has now become the most serious disease of dogwood. When planting a new dogwood, choose powdery mildew resistant cultivars.
- The early symptoms begin in mid to late May as leaf spots with tan or purple borders. In wet weather, these spots can rapidly enlarge and kill the entire leaf. These blighted, drooping leaves can remain hanging on the branches in wet weather before defoliation occurs.
- The disease spreads from infected leaves into the twigs and branches and can cause dieback of the limbs. Young green stems and water sprouts are especially susceptible. Dark cankers will cause stem girdling and dieback. On older branches, the wood under the bark will appear dark brown in contrast to healthy light-colored wood. If the dieback reaches the main trunk the entire tree can be killed.
- To distinguish this disease from other leaf spots, examine the underside of the leaves (with a hand lens or magnifying glass) for numerous small tan to brown dots, about the size of a printed period, scattered within the blighted tissue. These dots are the source of spores that will be washed away by rain or dew, or spread by insects to healthy leaves and neighboring trees. The disease overwinters in twig and stem cankers that initiate new infections in the spring.
- Avoid digging native trees from the woods and transplanting them into landscapes. This practice can introduce the disease into a neighborhood that was previously disease free.
- Plant disease-resistant cultivars of flowering dogwoods. Tartarian dogwood (Cornus alba), red osier dogwood (C. sericea), and Cornelian cherry (C. mas) also are resistant to this disease.
- Avoid over-application of fertilizer which can result in succulent new growth with greater susceptibility to disease.
- Prune out all dead or dying twigs and limbs during dry weather. All water sprouts or suckers on trunks and branches should also be removed.
- In the fall, rake and remove fallen leaves. Remove any dead leaves still attached to the branches.
- Registered fungicides can be utilized on trees in landscapes in the spring at bud break, followed by additional sprays every 10-14 days until leaves are fully expanded. Trees should also be sprayed once in the fall after the leaves have changed color but before leaf drop.