Some Tree Diseases of the American South

Tree diseases are a major concern for horticulturalists and foresters in the American South. Decades ago the beautiful chestnut and elm populations in this country were nearly wiped out. Appalachian mountaintop forests of spruce have been decimated. The lumber industry has lost millions of dollars in damage due to disease. Hardwoods in the South are affected by several fungal infections. Root and butt rots affect the base or the roots, often attacking the tree through wounds or exposed roots. They injure and sometimes kill the tree by damaging the roots and the cambium. Other varieties of root rot also affect conifer trees.Wilts are fungal infections whose most visible symptoms are yellowing and wilting of the foliage. Though the effects of wilts are usually obvious in theleaves of a tree, most wilt infections enter the tree through the roots. Some wilt varieties are also transmitted from tree to tree by insects. Dutch elm disease is probably the most notorious wilt infection.Canker diseases are fungal infections that create areas of dead tissue under the bark of the tree. Cankers can girdle the tree by killing the live section of the bark, and create opportunities for insects and other fungi to damage the trees even further. Chestnut blight is a type of canker disease that has destroyed nearly all American chestnut trees.Other fungal infections that primarily affect hardwoods are anthracnose, which affects mostly shade trees and dogwoods, and cottonwood rust, which causes a lot of damage to cottonwoods in nurseries. They primarily damage the leaves and twigs of the tree. Black knot is a fungal infection that causes swellings in the branches and twigs of cherry trees. Conifer trees in the South are affected by several needle casts, blights and rusts that attack the foliage of the trees. In the wild, these fungal infections only cause superficial damage to the trees, but if they attack Christmas tree farms and other nurseries they can cause severe financial losses. Older trees usually recover, but repeated defoliations from the infections may kill saplings.Other rusts and cankers affect the cones and stems of conifer trees. Fusiform rust probably causes the most damage, but other diseases in this category include comandra blister rust, eastern gall rust and pitch canker. Another disease is southern cone rust, which requires two hosts to survive and propagate. This fungus is unusual because it depends upon both pine and oak trees to reproduce. Most tree diseases are caused by various types of fungi, but there are exceptions. Nematodes and parasites can damage the roots of trees, while mistletoe can attack the branches. Finally, environmental hazards such as air pollution and herbicides can cause serious harm to trees.