Chestnut Blight, Dutch Elm Disease, and White Pine Blister Rust

These three forest diseases have historically been important. They have dramatically changed the way the present forest looks. All of them were introduced from other continents. Both the American chestnut and the American elm have largely been eliminated from forests by these pests. Research is being conducted to find methods to control the diseases and identify varieties of these trees that are resistant to the diseases.
Chestnut Blight

Chestnut blight, caused by the introduced fungus Endothia parasitica, was first reported in the United States in 1904. In 1914, the survey of Maryland's forests reported that American chestnut trees were present in the forest. By the 1950 survey, nearly all of the American chestnuts larger than sapling-size had been killed by the chestnut blight. Young trees are not usually affected by the blight. Since American chestnuts produce seeds at young ages, and sprout prolifically, young trees can be found in Maryland. The fungus also attacks post oak, and causes minor injury to maple, hickory, and sumac trees.
The chestnut blight enters through wounds on trees or through the bark when it begins to split and furrow with age. Then, it produces cankers on branches and stems. Branch cankers kill branches causing leaves to turn yellow and wilt. Stem cankers girdle and kill trees.

This information provided by the Maryland Department of Natural Resources Forest Service