Diseases in Oak Trees
There are many diseases which attack both healthy and stressed oak trees. Most of these, are fungal. Some are more targeted to specific oak families; some can attack other species in addition to oak trees. The four outlined below are a sampling of the many diseases. If trees are treated by trimming, etc., please note that oaks should only be pruned from late March to early June.
The fungus disease, Anthracnose, is most commonly found attacking the White Oak group (Post Oak, Bur Oak, White Oak, Over Cup Oak). It is erupts in early summer when irregular brown spots are visible. Later in growing season, dark pustules can be found on the leaves. The fungus achieves its maximum rate of growth in hot, humid conditions, such as those seen in Houston.
Rust is a fungal infection which is incubated in pine trees and transferred to evergreen oaks. It is, therefore, most commonly associated with Live Oak trees. Infested trees have yellowish pustules on the lower sides of the leaves. It is primarily controlled by removing the host from the vicinity of the oak, although airborne spores can drift for some distance. If the host trees are removed, there usually is no need for further control.
Oak Wilt is an important disease of all oaks. Members of the White Oak group die very slowly after contracting the infection. They may appear healthy as the fungus is carried in the vascular system. Red Oaks die rapidly after getting the disease. The fungus is carried from tree to tree by insects and through root grafts. Control is maintained by destroying diseased trees quickly, including the stumps. The fungicide, Vapam, can also be used. This is an extreme method, and a professional should be consulted to confirm the diagnosis.
Hypoxylon Canker occurs primarily on trees in a stressed condition, such as those which have suffered through a drought, covered with excessive soil, or another malnourished environment. It may take a year or more for an infected tree to die. Control is achieved by maintaining the trees in a healthy condition. Avoid injury to the trunk and limbs and never apply fill soil around the trees. An infected tree can spread spores up to sixty feet. Since the fungus resides within the tree, there is no topical remdy.