Elm trees are popular across the temperate zones. They are seen in home landscaping projects and backyards, parks and along city streets.
Elms are hardy, resilient trees, but like any plant, can sometimes fall victim to disease. It's crucial to recognize signs of disease as soon as possible to be the most effective in controlling it, as those diseases are largely incurable and can be deadly.
Dutch Elm Disease
Elm trees can be a target for several different kinds of bark beetles, carriers of the fungus that causes Dutch elm disease. Symptoms depend on the type of beetle that has infected the tree. Wherever the beetles feed, whether it's on the leaves or the branches, the afflicted area will begin to wilt and change color.
The disease is a fungus spread throughout the tree through the same vessels that carry water and nutrients. In order to try to combat the fungus, the vessels will develop a gum-like substance. Unfortunately, the gum not only stops the fungus, but also stops the necessary nutrients from reaching all parts of the tree. Elm trees can survive for years after being infected with the fungus, but they will eventually die.
The impact of the disease can be lessened and the lifespan of the trees lengthened by taking measures such as applying insecticides and completely destroying any dead trees that have been infected.
Elm Phloem Necrosis
Elm phloem necrosis is a viral disease spread from tree to tree through an insect with the apt name of leaf hopper. A very specific disease, it affects only two types of elm trees, the American and winged. Leaves will turn color and wilt, the first signs of elm phloem necrosis. A more certain diagnosis can be made by cutting into the tree and taking a look at the inner bark. In a healthy tree, the inner bark is white; in an infected tree, the color is yellow or orange in hue with black or brown flecks, from which the disease gets its other name, Elm Yellows. The inner bark will also have a faint mint smell.
Trees may die any time from a few weeks to a few years after being infected, but there is no known cure and the disease is always lethal. The disease attacks the most vulnerable--and most vital--tissues of the tree: those that are responsible for the transport of food and nutrients throughout the tree.
Wetwood manifests itself as a yellowish discoloration of the bark of the tree, usually the main trunk. This is caused by a buildup of fluid and gases within the tree, which then causes the bark to split. A thick slime can be seen leaking through the wounds in the bark; the slime is toxic, and prevents the growth of new cells that would otherwise heal the opening.
There is no cure for the bacterial disease, but it can be slowed by fertilizing the trees and inserting drain tubes to release some of the moisture building up inside the tree.
A number of insects feed on the slime, but are not carriers of the disease.