Black Spots on Dogwood Leaves

Identification

• An infection from the fungus Discula destructiva causes the dogwood anthracnose disease in dogwood trees. The fungus does not have any other hosts besides dogwood. If not controlled in time, disease can cause severe damage to trees. The causal fungus is transported to healthy trees by birds and insects and with splashing water.

Symptoms

• Disease symptoms start to appear on trees after all leaves have grown. Characteristic signs include the appearance of lesions and spots of different size and shape on tree foliage. The tan-centered spots on foliage upper sides have reddish to purple margins while the areas beneath the lesions are covered with very small black or brown spots. As disease progresses, the infection also spreads to petioles and twigs.

Damage

• Infected foliage gradually starts to die, the dead leaves often remaining on trees all through fall and winter. The infection in the twigs and stems causes tan-colored cankers. Branches start to die, starting from the lower tree and moving upward. As the fungus moves into the trunk, the bark starts to split. Diseased trees die completely within one to three years. Saplings are dead within the same year.

Control

• Keeping trees in good health is among the best preventive measure against the disorder. Apply a 3- to 4-inch layer of mulch around tree, keeping it away from the trunk, and irrigate and fertilize the tree regularly. Plant the tree in a sunny, well-ventilated spot and avoid the use of overhead irrigation as the prolonged presence of moisture on foliage favors fungal growth. Start applying fungicides at bud break and repeat every two weeks until foliage is fully grown. Recommended fungicides include myclobutanil, chlorothalonil ans propiconazole.