Oak is a deciduous shade tree that belongs in the beech family. The tree's long life can span several hundred years. Generally thought of as a healthy hardwood tree species, oak can be susceptible to disease related to fungi. The most common fungi that can damage oak trees are anthracnose and oak wilt.
Anthracnose is actually a group of diseases caused by several fungi. The fungi, while different, are closely related, so they are referred to collectively as anthracnose. Periods of cool, wet weather will make anthracnose more prevalent and the symptoms more severe. According to scientists at Cornell University, anthracnose fungi can infect several parts of the oak tree, including stems, branches and leaves.
Stems can get lesions, and new buds or shoots may die off. Cankers can form on the branches of the oak tree where twigs and stems have died. Leaves will have dead spots. A common anthracnose symptom in the spring is the defoliation of the tree, followed by a second growth of leaves sprouting in the summer.
Anthracnose survives the winter in leaf debris. It produces spores in the spring that become airborne and germinate on new buds. New spores are spread through rain. Anthracnose can be managed by cleaning debris in the fall. Prune infected parts of the tree. According to scientists at Cornell University Plant Disease Diagnostic Clinic, a fungicide containing chlorothalonil or mancozeb can be used to help control anthracnose.
Oak Wilt Symptoms in Red Oak
Oak wilt is an aggressive fungal infection that can kill a red oak tree in a month. Symptoms will be different, depending on the species of oak. Red oaks will have rapid discoloration and wilting in the leaves. Foliage will look bronze in color. The leaf will either be affected from the tip and move toward the base or the side to the vein. The tree will drop almost all of its leaves after the onset of symptoms.
White Oak and Texas Live Oak
Oak wilt kills white oaks, a branch at a time over a few years. U.S. Forest Service agronomists say that the leaf discoloration is different in the white oak, in that it proceeds from the margin to the base. Texas live oak trees will exhibit yellow veins that later turn brown and fall off the tree. This type of oak tree will die within six months of the contracting the fungal infection.
Infection Spread and Treatment
Oak wilt fungus infects other trees by moving through underground roots or above ground by insects. When the fungal infection transfers through the underground root system, it can kill oak trees in clusters. Because the infection is systemic, it moves rapidly through the cluster of oak trees. Insects, such as the nitidulid beetle, act as the carrier of fungal spores from infected trees over long distances to oak trees. The fungus spores carried by insects enter the tree through wounds and create an infection. There is no cure for oak wilt, other than to isolate and destroy trees that become infected.