Dutch Elm disease is a fungus that primarily attacks Elm trees, and was introduced to the Eastern US from Europe in the 1930s, carried in Elm logs that were for veneer. The disease slowly spread across the nation until in 1970 it reached the West Coast.
Dutch Elm Disease has one main symptom, which is wilting. Wilting is when the branch of the tree droops closer to the ground, and these symptoms normally begin in the canopy of the tree. When you peel back the bark of the tree you can see that it has black streaks in the wood. The disease spreads through the tree like a virus and once it meets the trunk of the tree the leaves fall off.
The disease can be transmitted from tree to tree in two ways. The fastest is through root grafts which occur when two trees are placed very near to each other allowing their roots to tie together. The disease has the ability to travel through these root grafts to infect more trees. The European Elm bark beetle is the the other main way of transporting the disease to different trees. The beetles live inside dead trees and carry the spores with them, giving the fungus entry into a new tree where it can breed.
A tree that has Dutch Elm Disease is almost impossible to cure, therefore it is usually more prudent to attempt to prevent the disease spreading to other trees. In order to stop the fungus from spreading by grafting, a two foot trench must be dug around the infected tree. To stop the European Elm bark beetles the tree would have to be immediately cut down and then burned. This disease is so dangerous to Elms that it should be reported to the County Department of Agriculture immediately when sighted.
The Dutch Elm Disease highlights man's inherent ability to disrupt nature: it was created as part of a system of checks and balances. In Europe at the time the disease erupted there were many Elm trees, and nature was trying to deplete the population. But due to man, who brought the disease to the US, which was not supposed to happen, the fungus grew too large. And that is why it is so common today.