There are numerous diseases that infect many species of trees, often permanently damaging or killing them. Oaks are vulnerable to bark diseases during all seasons, and can be killed by such diseases with extreme swiftness. Most of these bark diseases are caused by small insects and microscopic pathogens. In the case of insects, the diseases are usually classified as infestations. An infected oak tree is usually known as a host for a disease.
Sudden Oak Death
Sudden oak death is caused by a pathogen known as Phytophthora ramorum. This pathogen can be readily spread through the air, but is most often spread through natural paths of flowing water, such as rivers or streams. The symptoms of this bark disease consist of a darkening of the sap, a wilting of new oak shoots, and a browning of leaves. Often, this disease causes the oak's bark to split and produce darkened sap, which will stain the portions of the tree below the point of splitting. Usually, this disease does not directly kill the oak. Instead, it renders it more vulnerable to attack by insects that will slowly dismantle the tree. These insects include the bark beetle and the ambrosia beetle, which bore into the tree and eat the tree from the inside. The pathogen that causes sudden oak death can be detected using DNA sequencing, as well as recognised through the symptoms of the disease. If the disease is detected and the infected trees can be removed, it is possible to eradicate the disease in the area.
Oak wilt is an infection caused by a fungal pathogen known as Ceratocystis fagacearum. This fungus is usually spread locally from the root system of one tree to the root system of another tree. This type of spreading can occur over distances up to 15 feet. Over long distances, the fungus can travel through nitidulid beetles, which can travel miles. These beetles carry the spores of the fungus. They proceed to travel long distances, spreading the spores to other oak trees. Most often, this bark disease is recognised by a discolouration in the leaves of the oaks that it affects. It kills the oak tree by blocking the tree's vascular tissue. This prevents nutrients from travelling up the tree. Infected trees usually die from the top down.
The Twolined Chestnut Borer
The twolined chestnut borer is an insect (approximately .25 to .5 inch in length) that inflicts damage on the inner bark of many trees, but primarily infect oaks. It usually burrows through the bark of oak trees, leaving a distinctive D-shaped hole in the outer bark. The insect usually eats through the phloem and xylem of the trees. The phloem transports food within the tree, while the xylem transports minerals and water. The destruction of these two structures is usually deadly to the tree. However, the borer usually eats indiscriminately. This means the infected tree will lose its limbs in a seemingly random manner. The tree will die after two or three years of infestation by these insects.