Issue 7, July 22, 2022
Botryosphaeria Twig Canker and Dieback on Oak
The U of I Plant Clinic receives numerous oaks samples each summer. Many of these samples were sent to the clinic by clients concerned about oak wilt. Fortunately, only a small portion of the samples turn out to be infected with the disease. The remaining samples often have other pest or disease problems with symptoms resembling oak wilt.
The U of I Plant Clinic recently diagnosed several oak samples with Botryosphaeria twig canker and dieback. Botryosphaeria canker is a common disease that we see on many ornamental plants and fruit crops. Oak, crabapple, sweetgum, dogwood, elm, and redbud lead the list at our clinic. On oak, the disease is caused by the fungal pathogen Botryosphaeria quercuum. Browning leaves at the ends of the branches is usually the first clue to a problem, with the canker itself often going unnoticed. As the canker girdles the stem, leaves begin to wilt, turn yellow, and then brown. Some young twigs may curl downward. Affected trees show a wilting or "flagging" of the terminal growth on the ends of branches, which may lead someone to suspect oak wilt. However, Botryosphaeria twig canker and dieback only affects the ends of branches, whereas oak wilt affects entire branches.
If the stem is not entirely girdled, it may show one-sided death, or some leaves are affected and others are green. Botryosphaeria cankers are usually cracked, dry, and discolored. Fruiting bodies of the fungus appear as pinhead-sized black specks embedded in the bark. Often, these fruiting bodies appear as small bumps covering the canker.
Botryosphaeria and other canker fungi are known as stress pathogens. The first step toward disease management is identifying the source of stress. Try to correct or modify the site, soil, or surrounding plants to make the conditions less conducive to cankers. This might involve diverting drainage away from the plant, pruning surrounding plants to allow better airflow, fertilizing the tree, providing water in drought, etc.
Author:
Travis Cleveland