Anthracnose - Oak

Anthracnose on white oak can be common in the spring. Leaf symptoms range from large areas of browning, especially on the leaf margins, to scattered small necrotic spots. The leaves have an overall scorched appearance. The lower branches tend to show the most severe symptoms.

The disease is caused by the fungus Apiognomonia quercina and is favored by rainy spring weather. Oak anthracnose can occur over a wide range of temperatures, but lower temperatures promote the most severe symptom development. Midsummer conditions tend to cause outbreaks to subside.

Acervuli, fruiting structures of the pathogen, eventually become visible on the undersides of leaves, especially in the necrotic areas next to leaf veins.

Twig infections may also occur, causing dieback before the buds open in the spring. The fruiting structures on the dead twigs can provide a source of spores to infect emerging leaves.

Although unsightly, anthracnose is a minor problem on established trees. Basic cultural practices such as mulching, proper watering, and removal of fallen leaves will help maintain tree vigor. Remember, oaks should not be pruned during April, May, or June. Pruning wounds can attract the beetles that spread the oak wilt fungus.