Dutch elm disease is a fungus called Ophiostoma Novo-ulmi. This fungus grows only in elms – like American elm and Siberian elm trees. The disease is spread from infected trees to healthy trees most commonly on the elm bark beetle, Scolytus multistriatus. It can also pass from one tree to another through root grafts, a situation where a tree’s roots fuse underground with another tree of the same species.
Although there are several ways to treat for Dutch elm disease, the best method is to prevent the fungus from infecting your tree. One application of Arbotect® fungicide can protect a tree for up to three years. Arbotect® gives greater than 99% success over 3 years when applied properly. Arbotect® does not work if the tree already is infected with Dutch elm disease or the disease fungus enters the tree through root grafts.
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Dutch Elm Disease Treatment Option 1
Protecting with Arbotect®
The purpose of preventive macro-infusion with Arbotect® is to provide even and complete distribution of the fungicide throughout the 2-4 year old twigs were the beetles feed. Trees should be treated after the leaves have fully enlarged or after the seeds have dropped. The treatments can be administered until there is fall color present in the canopy. Arbotect® does not work if the tree already is infected with Dutch elm disease.
Diseased elms should not be treated with Arbotect®. Our experience is that Arbotect® will mask the symptoms of the disease for 1-3 seasons before the tree dies. Arbotect® does not prevent infections that grow through root grafts, so in situations where this is a concern , install a trench and wait until the following season to make sure the tree is healthy before protecting with Arbotect®. As a preventive treatment this process gives highly predictable results.
Dutch Elm Disease Treatment Option 2
Saving infected elms with tracing
Tracing is a method of saving recently infected elms, where diseased portions of the tree are removed. Although this process can be effective, only trained professionals should trace elms. Only the earliest stages of Dutch elm disease can be stopped by using this method, and it still requires the use of fungicides. The most effective method of treating individual trees for Dutch elm disease remains to be preventative Arbotect® applications. Contact a tree geek for more information.
Dutch Elm Disease Treatment Option 3
Root graft disruption
Root graft disruptions involve physically cutting the roots shared by healthy and diseased trees through a process called trenching. This is most reliably accomplished mechanically with either a trencher or vibratory plow. Remove the diseased elm only after common roots have been disrupted. Contact a tree geek for more information on disrupting root grafts.
How Is It Spread?
Dutch elm disease spreads from tree to tree in two ways.
1. Beetle spread of Dutch elm disease
Beetle infections generally start in the 2-4 year old twigs, where the beetle feeds and mates. The fungus rubs off the beetle and begins to grow in the tree in a downward pattern. Once it has reached the root flares, the fungus can spread to other trees through root grafts, as well as throught the tree. The characteristic stain on the xylem of an elm infected with Dutch elm disease is caused by the tree producing gum-like substances, called tyloses, in an attempt to stop the spread of the disease. These tyloses cause the tree to wilt and die.
2. Root graft spread of Dutch elm disease
The other method of disease transmission between elms is through grafted roots. When elms are growing near each other their roots come in contact in the soil and graft together. The Dutch elm disease fungus can pass from diseased to healthy trees through these grafted roots.
The first evidence of Dutch elm disease is wilting or “flagging,” leaves on the infected branches turning dull green to yellow and curl, finally becoming dry, brittle, and brown. The symptoms progress down the limb and eventually throughout the entire tree. If bark is peeling off the infected wood, the water conducting vessels will reveal the brownish staining caused by tyloses.
Understanding the Dutch elm fungus and how it grows makes diagnosing this disease easier. A few key distinctions will help in accurately making sure that you are in fact dealing with this dreaded disease.
1. Leaves on infected trees are almost always curled or wilted looking. They often drop off. Leaves that are flat and shiny are common in the late summer and are usually caused by branch senescence.
2. Dutch elm disease symptoms progress as the fungus grows in the tree. Thus, there is a pattern of leaf death outside the tree that reflects the fungus growth inside the tree.
3. Check under the bark close to where there are external leaf symptoms. Dutch elm disease always causes the water conducting vessels to turn a dark brown. Finding this discoloration along with wilting leaves is a very good indicator that Dutch elm disease is present. Use a chisel and a hammer to open a hole in the bark to check for the discoloration.
4. If you are unsure if your elm has Dutch elm disease send photos to a tree geek. Use our tree diagnosis form.
Distinguishing Dutch elm from look-alike problems
Drought symptoms in an elm usually shows up as sporadic yellowing flat leaves that are dispersed throughout the tree canopy. Whereas Dutch elm disease causes the leaves to curl and the dieback is usually thorough in one or more section of the tree.
If the lower leaves are visible, you will see flat leaves that have small whitish spots or if the infestation is sever, the leaves will take on a tan appearance.
Look for strange branch angles which are a good indicator of broken branches. Broken branches often will hang down and the symptoms on the branch will not progress. The use of binoculars can be a good tool to distinguish the difference.
Drought, leaf miner
Spring through summer
Risk of Spreading