Red Oak Problems and Leaves That Turn Brown

Oak Wilt

• Leaves often turn brown on a red oak if the tree is infected by the pathogen Ceratocystis fagacearum, a fungus that results in the condition known as oak wilt. This disease can affect nearly all species of oak and is especially problematic in the red oak family. Oak wilt begins its lethal progression from the crown downward and showcases itself when leaves begin to wilt, and turn a tan, bronze or brown color along their edges.

Wilt Effects

• At the same time as the red oak leaf is turning brown, it begins to droop and roll inward, lengthwise. Oak wilt continues to progress down the tree, and the health of the leaves worsens; eventually they turn yellow and fall away. Oak wilt is extremely lethal and most of trees that contract this disease will die within one year, although occasionally they survive two years or more. Pruning away infected branches has little effect, and mechanical devices should be sterilized to ensure the fungus is not spread to other plants. In most instances, the tree should be removed and destroyed.

Anthracnose

• A separate fungus called Apiognomonia quercinia causes the disorder known as anthracnose, highlighted by scattered brown spots that pop up along the veins of the red oak leaf. It may be accompanied by a curling of the margins. Anthracnose is especially prevalent when the spring or growing season has been exceptionally wet as infected plants contain spores that spread easily through rain and wind. The condition is typically most severe in the lower sections of the tree where humidity is highest.

Iron Chlorosis

• Iron chlorosis is a nutritional deficiency that develops in a red oak when too little iron is present in the surrounding soil. The lack of iron causes the tree to be unable to conduct photosynthesis properly. As a result, the leaves of the tree will scorch, showcased by the development of brown spots within the leaf margins and along the edge. The application of iron chelate, in addition to ammonium sulfate or sulfur, can help to rectify the iron deficiency in the earth.