The American beech (Fagus grandifolia) tree is a large, attractive, deciduous shade tree that has smooth, gray bark and green leaves that turn bronze in the fall. The tree, which can reach heights of 120 feet, is native to North America and has strong wood. Most American beech tree diseases, save one, are only cosmetic and are not dangerous to the life of the tree.
Scale are small, sucking insects that feed on plants. Often found lining the stems of plants, they can be difficult to remove or kill. Beech scale attach themselves to the smooth gray bark of the beech tree, piercing the tree with their long, sharp sucking parts. There they stay, weakening the tree over time.
A large scale infestation can weaken the American beech tree, which makes it much more susceptible to other diseases. In fact, the biggest danger scale pose is that they are carriers of a fungus that can be deadly to beech trees. While scale alone will only weaken the tree, if they carry the Neonectria fungus with them, it can cause a fatal disease.
Beech Bark Disease
Neonectria causes beech bark disease. This fungus is carried on the bodies of sucking insects--most notably scale, as mentioned in section 1--and can lie dormant in a tree for up to 19 years. Once the fungus begins colonizing and killing the wood of the tree, it can set off a vicious cycle. The disease causes American beech trees to eventually snap as the wood in the trunk dies. The disease also kills any new trees that sprout from the dead tree.
Beech bark disease cannot be cured, but scale can be controlled on single trees with the application of insecticides.
Leaf spot is a disease that causes unattractive, dark spots to appear on the leaves of the American beech tree. Leaf spot is caused by a number of fungi and can take slightly different forms depending on the specific fungus. In some cases, the spots spread to overtake the leaf, which turns brown and drops off prematurely. In other cases, the spots are tiny, causing the leaves to appear speckled. Other fungi cause the spots to fall out of the leaves, leaving them with a holey appearance.
The fungi that cause leaf spot spread through drops of water, so warm, wet springs can contribute to the rise of this disease. A preventative fungicide can be applied to trees in early spring if they are small enough.