Beech trees (Fagus species) are desirable for their smooth, gray bark, large size and attractive shapes. Some varieties, like the Japanese beech, thrive in full shade; while others, like the weeping European beech, prefer full sun. The American beech, as its name implies, is native to the United States and is popular with home gardeners who want a sturdy, long-living shade tree. Beech trees can suffer from several minor diseases and one serious, life-threatening disease.
Beech Bark Disease
Beech bark disease causes significant amounts of beech trees to die each year, according to David R. Houston and James T. O'Brien, plant pathologists with the United States Department of Agriculture. The disease is caused by the fungus Nectria coccinea, which is carried on the bodies of beech scale, a small, sucking insect. Beech scale burrow through the bark of the tree to suck out the sap. The fungus enters the sap wood of the tree, where it can lie dormant for as long as two decades.
As the fungus invades and colonizes the tree, small sections of the trunk begin to die. As the disease progress, new spring leaves do not develop fully. They may not open, or they may open and turn yellow. Some may fall prematurely from the tree. In time, the wood becomes so infected and weakened that the tree will snap and fall to the ground. This may happen in stages, or all at once.
There is no cure for beech bark disease once it has invaded a tree, but insecticides can control and prevent the scale insects that carry the fungus from feasting on the sap of beech trees.
Bleeding canker is a disease that causes unattractive cracked areas of wood to develop on beech trees, which often ooze a thick, gooey, brown liquid. These dead areas of wood can sometimes completely encircle a branch of the tree, causing the flow of nutrients to be cut off, and the twig to die from the tips inward. This is called "dieback" and can also occur from the crown downward if the trunk is girdled. The latter is very rare, however.
The fungus Phytophthora cactorum causes the areas of wood to die. This fungus is carried on the bodies of sucking insects, such as aphids and scale. The fungus can also enter a tree through a wound caused by gardening tools. Branches with cankers should be pruned off below the canker to prevent the disease from spreading. Bleeding canker cannot be controlled or cured with chemical sprays.
Leaf spot is caused by numerous types of fungi that are spread on water. Exceptionally wet spring weather can contribute to the rise of this disease. Windblown rain can transfer the disease from one tree to another. While leaf spot is unattractive, it is not life-threatening for the beech tree.
Symptoms appear as tiny spots on the leaves, which can range in color from orange to black, depending on the particular fungus. In some cases, the spots have a purple or white halo. In others, the spots have a greasy appearance. The spots may merge to cover the leaf, causing it to become malformed or drop from the tree. Or, the spots may fall out of the leaf, making it appear as if the leaf with shot through by a gun.
The fungi that cause leaf spot can also affect the blossoms of the flowers, causing them to turn brown and wilt. These fungi can be controlled with a systematic application of fungicide in early spring and fall.