The flowers, foliage and roots of Cornus florida, commonly known as flowering dogwood, can attract a variety of diseases. Although some flowering dogwood tree diseases only cause minor damage, others can lead to the death of the tree. Properly planting your flowering dogwood and following good practices in the garden can often prevent the onset of disease.
Spot anthracnose causes small, reddish spots to form on the bracts, leaves and shoots of dogwood trees. On the leaves, the spots often have yellowish-gray centers that may fall out, leaving holes in the leaves. The spots often merge and infected foliage grows in a stunted and irregular manner. This disease typically affects dogwoods during cool, wet spring weather but rarely causes significant damage to the tree. In severe cases, apply fungicidal sprays containing chlorothalonil or mancozeb according to the directions on the product. Clean up and dispose of fallen foliage to prevent the disease from overwintering in your garden.
Leaf spots similar to those of spot anthracnose develop on dogwood trees infected with discula anthracnose. This disease leads to the development cankers which can cause the dieback of branches and the eventual death of the tree. Prune back infected branches and disinfect the pruning tool between each cut with rubbing alcohol. Spray fungicides containing chlorothalonil and mancozeb during leaf emergence in the spring, following the directions on the product. Avoid planting flowering dogwood trees in wet, shaded areas to prevent this disease.
Septoria Leaf Spot
Septoria leaf spot causes dark brown or purple spots to form on the leaves of flowering dogwoods. The centers of the spots turn gray over time, but this disease does not cause long-term damage. Septoria leaf spot develops in mid to late summer just before leaves begin to fall from the tree, so fungicides are rarely necessary. To prevent the disease from overwintering, pick up any fallen leaves around the tree.
The fungal disease powdery mildew produces a layer of white fungus over the leaves and shoots of dogwoods. Infected leaves are often smaller than healthy leaves and may appear deformed. Wet weather, warm days and cool nights encourage the development of powdery mildew. Application of fungicides before the appearance of this disease may help to prevent it. Spray trees with triadimefon, potassium bicarbonate or Neem oil extract according to the product's instructions.
Several different fungi can cause root rot of dogwood trees. These fungi often survive in the soil and attack the roots when the tree is stressed due to injury or undesirable growing conditions. The infection spreads up the tree from the roots, causing girdling and dieback of branches and yellowing of leaves. Plant flowering dogwood trees in well-drained soil to prevent root rot. Once the signs of infection become noticeable, the tree cannot be saved. Remove the tree and its roots and as much of the surrounding soil as possible to prevent the disease from spreading to nearby plants. Avoid planting new trees or other plants in that location.