Understanding Elm Scale Symptoms: Identifying and Treating the Infestation

Elm scale, a common pest for Elm trees in Calgary

Elm trees are beautiful and iconic trees that are found throughout Calgary. Unfortunately, these trees are susceptible to a range of pests and diseases, including elm scale infestation. Elm scale is a common insect pest that feeds on the sap of the tree, causing damage to the bark and leading to a range of symptoms. In this blog post, we will explore the symptoms of elm scale infestation and provide tips on how to identify and treat the issue. We will also discuss how to prevent elm scale infestation and keep your trees healthy. Whether you're a homeowner or a professional landscaper, this guide will help you identify Elm scale and keep your elm trees looking healthy and beautiful.

What is Elm Scale?

Elm scale is a small insect that belongs to the family Diaspididae. It is often found on the bark of elm trees, where it feeds on the sap of the tree. Elm scale can be identified by its small, flat, oval-shaped body that is about 3 mm to 6mm in size. The insect has a hard outer shell that protects it from predators and environmental factors. Elm scale can be found on the bark, leaves, and twigs of the tree and can cause damage to the tree if left untreated.

Elm scale infestation can lead to several issues in trees, including leaves that turn yellow, slower growth, black sooty mold on the bark, and branches that begin to die. At first, these symptoms might not be easy to recognize, but if they're not addressed, they could get worse. In some cases, if the problem is left untreated, it might even result in the need for tree removal, underscoring the importance of early action. It is important to identify elm scale infestation early and take steps to treat the problem before it causes serious damage to the tree.

Symptoms of Elm Scale Infestation

One of the most common symptoms of elm scale infestation is the presence of a sticky residue on the leaves and branches of the tree. This residue is actually honeydew, a sugary substance that is excreted by the insects as they feed on the sap of the tree. The honeydew can attract other pests, such as ants and wasps, which can further damage the tree.

Another symptom of elm scale infestation is yellowing leaves. The insects disrupt the flow of nutrients and water throughout the tree, which can cause the leaves to turn yellow and fall off prematurely. This can lead to stunted growth and a weakened tree overall.

In severe cases of elm scale infestation, the tree may experience dieback, which is when branches or sections of the tree start to die off. This can be a serious problem and may require professional intervention to save the tree.

It is important to note that these symptoms can also be caused by other pests and diseases, so it is important to properly identify the cause of the symptoms before taking any action. Our professional arborist can help identify the cause of the symptoms and recommend an appropriate course of action.

An almost tell tale sign of elm scale is its companion fungal disease, black sooty mold. This mold thrives on honeydew, it can envelop the leaves, branches, and bark of the tree, causing it to have a blackened appearance. This can cause the tree to weaken over time, making it more vulnerable to other pests and further infection. It can and will also develop on your deck, sidewalk and any other structures where the honeydew is raining down on. While the black trunk and green canopy can look appealing on the landscape, its effects on the tree can be devastating.

Black sooty mold on a elm tree

Treating Elm Scale Infestation

There are several steps you can take to treat an elm scale infestation and prevent further damage to the tree. Here are some of the most effective methods:

· Prune affected branches: If you notice that only certain branches are affected by elm scale, you can prune them off to prevent the infestation from spreading. Be sure to dispose of the branches properly to prevent the insects from spreading to other trees. (This method can only be done between October 1st and March 31 st due to a province wide pruning ban.)

· Use horticultural oil: Horticultural oil is a natural oil that can be applied to the tree to suffocate the insects. This is a non-toxic method that is safe for the tree and the environment. This method is most effective before bud break in the spring during dry, warm weather.

· Apply insecticide: If the infestation is severe, you may need to apply an insecticide to the tree. There are not many insecticides available on the market that are effective against elm scale that are registered for use in Canada. We find in this situation, its best to hire a professional as tree trunk injections are our recommended route.

· Pressure wash affected branches in the early spring or just after leaf drop in the fall. You can also pressure wash off the black sooty mold, which will aid in helping the vigor of your tree.

· Fertilize: Deep root fertilizer is an excellent choice to help give your elm tree some vigor to help it deal with the infestation.

It is important to note that all of these methods have their own pros and cons, and the best course of action may vary depending on the severity of the infestation and the condition of the tree. If you are unsure about the best way to treat an elm scale infestation, it is always best to consult with our certified arborist who can provide guidance and expertise.

Preventing Elm Scale Infestation

Preventing elm scale infestation is much easier than treating it once it has already taken hold. Here are some tips for preventing elm scale infestation:

· Keep your tree healthy: A healthy tree is less susceptible to pests and diseases. Make sure to water your tree regularly, fertilize it when needed, and prune it regularly to promote healthy growth.

· Monitor your tree regularly: Regular monitoring of your tree can help you catch elm scale infestation early, before it becomes a serious problem. A big tip off that elm scale is taking a hold of your tree is the presence of black sooty mold. Watch for branches  developing a dark complexion on them. While not always elm scale that causes this, it's best to address the change before it becomes a major issue.

By following these tips, you can help keep your elm trees healthy and free of elm scale infestation.

A Mature elm tree with a scale and sooty mold problem

My Conclusion

Elm scale infestation is a common problem for elm trees and can cause serious damage if left untreated. Early identification and treatment are key to managing the infestation and preventing further damage to the tree. If you suspect that your elm tree is affected by elm scale, it is important to take action immediately.

In this blog post, we have covered the symptoms of elm scale infestation, its causes, and effective treatment methods. We have also provided some tips on how to prevent elm scale infestation in the first place.

Remember that prevention is always the best course of action when it comes to protecting your trees from pests and diseases. By following the tips we have provided and staying vigilant, you can help keep your elm trees healthy and beautiful for years to come. If you have any questions or concerns about elm scale infestation, be sure to Call us for a consult.


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