Oak trees are a member of the beech family and are famous for producing excellent hardwood lumber. Their wood is durable and attractively grained and is used to make flooring, railroad ties, barrels, and veneer. The oak is a symbol of strength and endurance and can live for more than 200 years. It is a relatively healthy tree, but it is susceptible to several serious and even life-threatening diseases.
Caused by fungi, anthracnose occurs after unusually cool, damp weather during budding. Signs of anthracnose are repeated early leaf loss, dead buds, and scattered brown spots or blotches on leaves that appear along the veins and give leaves a burnt look. One attack of anthracnose is not harmful to a tree, but yearly infections can weaken trees, allowing them to become susceptible to more dangerous diseases.
Control anthracnose with chemical fungicides. Prevent anthracnose by removing infected leaves in the fall, prune and burn dead twigs and branches and thin the crown of the tree, which promotes faster drying of leaves.
The fungal infection oak wilt affects all species of oaks. It is almost always fatal in red oaks. Signs of oak wilt are leaf damage, trees losing their green color, and yellowing or browning leaves along the outer edges. Leaves may look limp and appear to be wilting. As the disease progresses, leaves begin to fall.
There is no cure for oak wilt. Preventative measures are the only sure way to control the disease. Destroy infected trees and burn, chip or cover the wood in plastic for six months. Bury the edges of the plastic at least 6 inches deep and remove plastic when wood appears completely dry.
First seen in the midwestern United States, oak tatters is a relatively new disease. Symptoms of oak tatters start in late May. The first signs are the lack of veins in leaves. New leaves may have a lacy or tattered look to them and trees appear lighter in color or look as if they are lacking leaves. The tree begins to regenerate replacement leaves that may not have tatters but can be smaller and lighter in color. The quick production of the new leaves reduces that energy levels of the infected trees, causing excess stress to the tree.
Oak tatters cannot be treated or reversed. Good fertilization will help nourish and revitalize infected trees.
A common bacterial infection that affects the core and bark of many shade trees, wetwood is often found in oak trees. Symptoms include a yellow-brown discoloration of the wood and a foul-smelling slime that oozes from wood and branch crooks. When it dries, it leaves a crusty white substance on the tree. Insects are attracted to the slime and may feed on it, causing more damage.
There is no way to eliminate wetwood disease. Trees may survive if diseased bark is cut away when symptoms first appear. Most trees will need to be cut and burned to stop the spread of the disease.
Appearing in the spring and fall, powdery mildew attacks when the weather is cool and humidity is high. It is a common fungal disease and gives leaves the look of having been dusted with powder or flour.
Prevent powdery mildew by planting trees in sunnier areas, space plants well to allow for aeration, and prune and thin out the crown of the tree. Treat powdery mildew with fungicides.