There are tree diseases that attack hardwoods trees which ultimately cause death or devalue a tree in the urban landscape and rural forest to the point where they need to be cut. Five of the most malignant diseases have been suggested by foresters and landowners at About's Forestry Forum. I have ranked these diseases according to their ability to cause aesthetic and commercial damage. Here they are:
#1 - Armillaria Root Disease:
The disease attacks hardwoods and softwoods and kills shrubs, vines, and forbs in every state. It is pervasive in North America, commercially destructive, a major cause of oak decline and is my pick for the worst disease.
The Armillaria sp. can kill trees that are already weakened by competition, other pests, or climatic factors. The fungi also infect healthy trees, either killing them outright or predisposing them to attacks by other fungi or insects.
More on Armillaria root disease.
#2 - Oak Wilt:
Oak wilt, Ceratocystis fagacearum, is a disease that affects oaks (especially red oaks, white oaks, and live oaks). It is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests and landscapes.
The fungus takes advantage of wounded trees - the wounds promote infection. The fungus can move from tree to tree through roots or by insects. Once the tree is infected there is no known cure.
More on Oak Wilt.
#3 - Anthracnose Diseases:
Anthracnose diseases of hardwood trees are widespread throughout the Eastern United States. The most common symptom of this group of diseases is dead areas or blotches on the leaves. The diseases are particularly severe on American sycamore, the white oak group, black walnut and dogwood.
The greatest impact of anthracnose is in the urban environment. Reduction of property values result from the decline or death of shade trees.
More on Anthracnose Diseases of Hardwoods .
#4 - Dutch Elm Disease:
Dutch elm disease primarily affects American and European species of elm. DED is a major disease problem throughout the range of elm in the United States. The economic loss resulting from death of high value urban trees is considered by many to be "devastating".
Fungus infection results in clogging of vascular tissues, preventing water movement to the crown and causing visual symptoms as the tree wilts and dies. American elm is highly susceptible.
More on Dutch Elm Disease.
#5 - American Chestnut Blight:
The chestnut blight fungus has virtually eliminated the American chestnut as a commercial species from eastern hardwood forests. You only now see the chestnut as a sprout as the fungus eventually kills every tree within the natural range.
There is no effective control for chestnut blight even after decades of massive research. The loss of American Chestnut to this blight is one of forestry's saddest stories.
More on American Chestnut Blight.