Through its longstanding partnership with Birmingham Botanical Gardens, several oak trees on the Birmingham Zoo’s 122-acre property were diagnosed with Hypoxylon canker, a fungus that typically invades red oak trees, including water oak and Southern red oaks, but can occur in any oak. Unfortunately, this fungus typically kills the tree when it is on the main trunk.
Over 75 trees on the Zoo’s property began displaying symptoms, leading Zoo officials to turn to the experts at Birmingham Botanical Gardens to diagnose. Upon inspection, Jim Jacobi, Extension Plant Pathology Specialist with Alabama Cooperative Extension System at The Gardens, was able to diagnose the trees with Hypoxylon canker. “It’s important to remove infected trees to limit the spread of disease and the risk to people and property, due to falling tree limbs. Contact a licensed tree removal company or a certified arborist for assistance,” says Jacobi. The Birmingham Zoo is currently working on having the infected trees removed from the property.
While the infected trees have been located at the Zoo, it is a regional issue and is not limited to this specific area. Hypoxylon canker fungus tends to invade trees after a drought. Due to the 2016 drought throughout Alabama, this disease has become very common this spring and several oak trees throughout the community have become infected. Once a tree is affected, it quickly begins to rot the sapwood of the tree. This increases the chance of falling branches, or in some cases, the entire tree may fall.
There are several symptoms to look out for when examining oaks on your property. As the fungus that causes Hypoxylon canker spreads inside the tree, the first symptom observed is often the dieback of branches in the top of the tree. The bark of infected trees typically sloughs off on the main trunk or branches in spring or early summer revealing tan or brown fungal growth that’s often covered in powder spores. In late summer or fall, the fungal growth often becomes hard and crusty, turning silver or black in color. The brown, silver or black streaks of missing bark running up the trunk of the tree are the best way to recognize Hypoxylon canker. To reduce the risk of damage from falling branches, trees infected with Hypoxylon canker should be removed as soon as possible.