Oak Tree Diseases: Part One

Although well-known as one of the most majestic of the woodland trees, the mighty oak is also subject to a variety of diseases that can afflict and in some cases kill this tree. If you plan on planting oak in your own backyard, you should learn about these diseases, their symptoms, and their treatment in order to ensure that you keep your mighty tree healthy.

Powdery Mildew

Several fungi species cause this oak disease, with symptoms consisting of white, powdery growth on the top and bottom of the leaves. This can lead to malformed foliage, which may also drop prematurely or shrivel. The white substance may also turn brown as it ages, with tiny black dots present as well. Although control is not usually needed, severe cases can be treated or controlled with several substances such as triadimefon.

Bacterial Leaf Scorch

This disease, caused by the Xylella fastidiosa bacteria, usually results in lack of vigor, dying back of leaves, inhibition of water movement, reddening or yellowing of leaves, and eventually death. It is usually observed during the fall, after a summer drought. It is a slow-moving and gradual disease, so it may take five to ten years before the tree must be removed. It is more commonly seen in species such as pin, red, white, and bur oak, as well as sycamores and several other tree species. Treatment usually consists of removing infected trees, while prevention takes the form of reducing the presence of weeds (which can host the insects that spread the disease).

Hypoxylon Canker

Although many species of oak are susceptible to this white-rot disease, it is known to particularly affect post, water, southern red, and blackjack oak. It mainly infects trees that have already been damaged by some stress, usually drought. As it spreads and forms cankers, the crown of the tree will die, followed by the sloughing off of bark in infected areas. It can also spread from one tree to another. As yet there is no effective treatment (although cutting off infected branches may help), so prevention in the form of stress reduction is the most effective way to ensure your trees remain healthy and free of this disease.

Oak Leaf Blister

Pin oak and white oak are particularly susceptible to this oak disease, also caused by a fungus. The most obvious sign is the presence of blisters on the leaves, usually lighter green than the rest (usually caused by an overgrowth of leaf tissue). Although not typically deadly, it can result in leaf drop. Treatment is not usually necessary.

Sources

Clemson Cooperative Extension