Understanding Common Diseases of Elm Trees

Elm trees hold a beloved place in many homeowners' hearts. Unfortunately, these stately shade trees have suffered greatly in recent years from both infestation and disease. For that reason, it is more important than ever to keep your elm trees in good shape. If you would like to increase your awareness of the perils they face, read on. This article will discuss two common diseases and how to keep them at bay.

Dutch-Elm Disease

The name of this disease is actually a misnomer, as the fungus at the heart of the problem can be traced not to the Netherlands but to Asia. Asian species of elm trees have long developed defenses against this and other diseases, yet Western elms remain highly vulnerable. The fungus that ultimately destroys trees with Dutch-elm disease is only half of the problem. The other half are the beetles that act to spread the disease from tree to tree.

These beetles—known appropriately enough as elm-bark beetles—are naturally drawn to elm trees. For whatever reason, they prefer this species of tree as a place to lay their eggs. When beetles that have hatched on an elm tree bearing the destructive fungus go off in search of a new home, they unwittingly bring the disease with them. As the beetles burrow beneath the bark to lay their eggs, the fungus begins to infiltrate the tree.

You can initially distinguish a tree with Dutch-elm disease by the patches of yellow leaves. These patches will first occur wherever the beetles have established their initial colony. An effective test for verifying the infestation involves breaking off a small branch in the apparently diseased portion of the tree. By peeling back the bark and slicing the branch in half diagonally, you will expose the sapwood inside. If this wood bears brownish streaks, chances are your tree has contracted Dutch-elm disease.

Verticillium Wilt

Verticillium wilt is yet another disease whose primary agent is a type of fungus. Here there are two species of fungus that may be at play: V. alboatrum and V. dahliae. These fungi are often to be found in common ground soil. Where present, they penetrate the tree by means of its root system. As they make their way higher through the tree, they act to close off the vascular system responsible for carrying water.

As with Dutch-elm disease, Verticillium wilt can initially be distinguished by patches of leaf discoloration. Be sure to mention such warning signs to a professional tree service. If you are able to diagnose the disease quickly enough, it can be treated by means of strategic watering and fertilization efforts. 

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