Oak trees are one of many tall shade trees found in forests that used as ornamental landscape. In good health, oak trees can provide shade, cooling and insulation around buildings when in full bloom. Oak trees can become diseased, leaving them defoliated and distorted. Some diseases can quickly kill trees. Identifying oak tree diseases helps in treatment and prevention of further infection to surrounding trees. Often, removal is the only known cure.
Examine the leaves. Look for small, scattered brown spots. This can be a fungal infection such as Anthracnose or a sign of the fatal Sudden Oak Death. Scorched leaves are also a sign of Anthracnose. Observe the leaves for a lacy or tattered effect; this is a sign of the Oak Tatters disease affecting emerging leaves. Distortion and a needle-like appearance are signs of Powdery Mildew.
Look at the trunk and bark. Signs of root loss can be seen by one side of the trunk becoming flat, indicating part of the oak tree has stopped growing. Dark cracks in the trunk are signs of insects or fungal invasion.
Check the condition of the twigs and branches. Oak tree girdler kills twigs. Look for distorted branches resembling witches brooms, which are a sign of Powdery Mildew. Check smaller branches less than 1 inch in diameter for Diplodia cankers; signs include increased foliage loss and browning leaves on weak branches or twigs.
Check the root system. Oak Root Fungus can turn the leaves turn brown. The leaves remain on the tree as it dies. Signs of Oak Root Fungus can be seen on the outside of the roots as fungal infections, dark cracks and bleeding sap around the trunk base.
Look for insects. Signs of insect infestation include browning leaves. Insects infecting oak trees include oak moths.
Think about the geography and climate. The Midwest United States is known for the Oak Tatters disease. Water mold is common in coastal areas and often results in Oak Root Rot. Look for Oak Root Fungus on trees with a shallow water table. High humidity and cool temperatures are ideal climates for Powdery Mildew to form on oak trees.