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What Do Black Spots On Maple Leaves Mean?

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When autumn rolls around, maple trees offer some of the most beautifully colored foliage that there is to see. But what happens when black spots appear on the leaves of this majestic tree? This article will explain what these unsightly spots mean and how to eradicate them so your maple trees can be restored to their naturally lush selves.

The unsightly black spots that appear on maple leaves are not detrimental to the tree’s health; however, they do harm the appearance of the tree and the gorgeous colors they present in the autumn. Fortunately, there are ways to treat and prevent the issue of black spots on maple leaves. 

If you would like to preserve the appearance of your maple trees by preventing black spots on the leaves, continue reading this article for helpful information and tips to keep your trees looking beautiful year-round. 

Black Spots on Maple Leaves Explained

As briefly mentioned above, the black spots that appear on the leaves of maple trees are not harmful to the health of the tree. While they may not be harmful to the actual existence of the tree, they do make for an ugly display of foliage. 

Cause of Black Spots on Maple Leaves

The black spots commonly seen on maple leaves are a fungal disease caused by the Rhytisma acerinum fungus. This condition is often referred to as tar spot disease

Fortunately, this fungus is seasonal and will die out during the winter months. However, if the ground is not cleared properly, it will rebound in the springtime. 

This fungus tends to grow in areas where there is little sunlight and a lot of moisture combined with leaves and other ground coverings. 

When the spores from the fungi are released, they are transported by the wind and water runoff to the trees, where they begin to grow and ruin your beautiful foliage. 

The next section will discuss how to identify tar spot disease in maple trees, so you know what to look for. 

How to Identify When Your Maples Have Tar Spot Disease 

It can be difficult to spot the beginning stages of tar spot disease if you are not sure of what to look for. When a maple tree’s leaves have been infected with the Rhystima acerinum fungus, yellow-toned spots will begin to form on the top of the leaf’s surface. 

As the season progresses into mid-late summer, the spots will begin to transform into dark spots that resemble tar. Hence the name tar spot disease.  These tar-like spots are usually around a half of an inch in diameter and have a rigid texture. 

If you look at the underside of the affected leaf, you will notice that the areas where the spots are located have a cupped shape. When the leaves drop during winter, the fungus will become dormant until spring, when their spores are released, and the growth process begins again. 

So that begs the question as to how you can prevent or at least greatly reduce tar spot disease on maple leaves. 

Preventing Black Spots on Maple Tree Leaves

The most effective method for preventing this fungus is to clear fallen leaves and debris on your property and especially away from the bases of the trees where the leaves fall the most. 

It is recommended that you burn the leaves and other affected debris at a minimum of 140°F to ensure the spores are killed. 

As with any fungus, Rhystima acerinum thrives in warm, damp environments created by organic materials like fallen leaves and other debris.  

Important tip: Oftentimes, people will compost their leaves, thinking that the fungus will die. However, if your compost pile does not generate enough heat to kill the spores, it will create an ideal environment for them to grow, and you will not have eliminated the problem. 

Make it a part of your routine to keep leaves and other organic debris from building up around the base of your trees and other parts of your property. This will significantly reduce the chance of your maples and other susceptible trees contracting the dreaded tar spot disease. 

Fungicides Can Be Used to Expedite the Elimination Process

Other steps can be taken to expedite the process of eliminating the Rhystima acerinum fungus on your property. Most home improvement stores sell fungicides that you can mix and spray on the affected trees and surrounding areas. 

Another option is to hire a professional to spray your property if you are having a significant problem or if you are particular about how your trees look.  

Most people do not go to this extent because although the spots are rather unsightly, they are not harmful to the actual life of the tree. 

So, let’s go into a little more depth about maple trees and tar spot disease. 

More About Maple Trees and Tar Spot Disease

Did you know that there are over 100 different varieties of maple trees? There are too many to list in this article; however, we will name the maples and a few other varieties of trees that are most commonly affected by tar spot disease. 

The trees most commonly affected by tar spot disease include: 

  • Black maple
  • Boxelder
  • Holly
  • Norway maple
  • Red maple
  • Silver maple
  • Sugar maple
  • Sycamore 
  • Tulip-tree
  • Willow

The next section will talk about having realistic expectations when dealing with the eradication and prevention of tar spot disease in your trees. 

Keep Realistic Expectations When Dealing With Tar Spots

If you live in a highly wooded area, it is important that you have realistic expectations when it comes to the treatment and prevention of this fungal disease. 

It is not always feasible or possible to treat and/or clear the entire forest floor. It can take quite an effort by many people to get this issue under control if it has spread to a large number of trees.  

Patience is key if you want to clear up this unsightly problem. It will likely take some time and heavier equipment than a wheel barrel and a rake to clear around the trees most affected by the fungus. 

The best time to get started is right after the leaves have fallen for the season and before the snow falls (if you live in that sort of climate). The more leaves and debris you can clear and burn, the better off you will be come springtime. 

Black Spots on Maple Leaves: No Reason to Worry

Now that you know what causes black spots on maple leaves and how to prevent or at least reduce the issue, you can help your trees get their beautiful foliage back so you can enjoy their shade and the beautiful colors they display when the seasons change to the colder months. 

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Jena Slocum Co-Founder

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