Dutch elm disease has killed millions of elm trees throughout the United States, Europe, and New Zealand.
The disease spreads rapidly because trees can infect one another through their root system.
Signs of Dutch elm disease include yellowing, curling, or wilting leaves, or leaves that drop prematurely.
Elm trees create striking, shady canopies in your yard, and also make effective windbreakers. Thanks to these benefits, as well as their natural beauty, elms have been planted in high numbers throughout Europe and North America.
Over time, a destructive disease carried by beetles emerged and started wreaking havoc on these stately trees. Dutch elm disease has wiped out millions of elm trees since the early 1900s, so read on to learn how it spreads and how to spot it on a tree in your yard.
What Is Dutch Elm Disease?
Dutch Elm disease is a destructive tree illness, caused by two types of fungi (Ophiostoma ulmi and Ophiostoma novo-ulmi) that infect native elms, as well as some other tree species. It spreads through the native elm bark beetle, the European elm bark beetle, and the banded elm bark beetle. The disease is responsible for killing off thousands of trees in the United Kingdom, Europe, New Zealand, and the United States.
How Does Dutch Elm Disease Infect Trees?
The infection process starts with female bark beetles looking for weak elm wood (or logs or firewood) to lay their eggs in between the tree’s bark and wood. If the beetle is carrying Dutch elm disease, fungal spores spread throughout the tree area, and when young beetles emerge, they are covered in the fungal spores.
These young beetles feed on the leaves and twigs of healthy trees, spreading the spores to the tree. The spores then start new infections, and once the tree is weak, the beetles colonize it, repeating the cycle. Since the fungus enters the tree’s vascular system, the spores spread anywhere water goes, including the root system. In addition to beetle spread, the fungus can naturally spread via root grafts up to 50 feet away. When a tree is infected through its root system, it moves very quickly throughout the rest of the tree.
What Happens When a Tree Contracts Dutch Elm Disease?
Typically, symptoms of Dutch elm disease begin to emerge in late spring. The tree leaves will wilt, turn dull green and then yellow or brown, start to curl, and might drop prematurely. There might also be brown or black streaking in sapwood (the former top layer of wood beneath the bark).
You can check for this by cutting a section of a dying branch and looking for discoloration. Some of these symptoms are very similar to other diseases, like elm phloem necrosis; therefore a formal diagnosis must be completed by a laboratory.
What Can I Do to Protect My Trees Against Dutch Elm Disease?
Dutch Elm disease is a ravenous, fast-moving disease, but there are some things we can do to mitigate its spread.
Burn, debark, or bury dead or weak elm wood (including logs) to prevent beetles from laying eggs.
Break the root grafts of larger trees that are within 50 feet of each other. You’ll need to hire a local tree service for this task.
An annual spray of the insecticide methoxychlor over bark surfaces can kill many beetles before they leave behind spores.
Some fungicides can prevent the beetles from spreading the infection. Application is expensive, repeated seasonally, and needs to be injected into the tree by a professional arborist or a tree service company.
Plant hybrid elms that are resistant to Dutch elm disease, such as New Horizon, Accolade, Regal, and Frontier. Another option is the Chinese elm, Ulmus parviflora.