Many of the questions that Extension fields are seasonal in nature.
It makes total sense. Gardeners ask questions that are related to what they are seeing or experiencing in the moment.
This is the situation that is being addressed in today’s column. I have had several people call, email, text or send photos through social media about maple trees. So I am going to try to tackle some of the common maple woes.
Unfortunately, sometimes answers aren’t cut and dried. Often there are multiple factors at play as we try to get to the root of the problem. And sometimes, the cause of what is observed is never fully diagnosed or understood.
Tar Spot: There are different fungi in the genus Rhytisma that result in the leaf diseases we call tar spot. The black spots form on the upper leaf surface and can be small individual dots the size of a tip of a pen, or larger spots that resemble droplets of tar.
Tar spot alone is rarely serious enough to threaten the overall health of the trees, but can become unsightly. Heavy infections can result in early leaf drop — a circumstance that causes the greatest concern because lawns are littered with fallen leaves prematurely.
Treatment is rarely warranted. The fungus will overwinter on the fallen leaves, so spores can be reduced by removing the fallen leaves. Spores can be spread by the wind, so even with a good cleanup, if the weather conditions are favorable, the disease will likely reappear.
Anthracnose: Anthracnose is another common leaf disease that we see on maples and other deciduous trees. These diseases are often found along the leaf veins, causing the area to become brown. Just as with tar spot, heavy infections can result in early leaf drop.
This season, many maple leaves were infected by both tar spot and anthracnose.
Verticillium wilt: This disease is more serious than tar spot or anthracnose. Verticillium wilt is caused by a fungus that lives underneath the bark in the xylem that is responsible for carrying water through the tree. The fungus essentially clogs the xylem, preventing water flow and causing the plant to wilt.
The disease can occur either acutely or chronically. In acute infections, a branch or a section of the tree may wilt and turn brown suddenly. Other branches usually follow, until most of the branches are wilted. Leaves may also turn yellow between the veins or may drop prematurely. Acute infections occur when the fungus is living in the newest wood.
In chronic infections, leaves may be smaller than usual, yellow and often with brown edges. The tree may grow poorly and sometimes produce heavy seed loads. The tree does not wilt or die quickly, but declines slowly over time. Chronic infections occur when the fungus is living in older wood.
This fungus lives in the soil and infects the plant through the roots, often entering through wounds. The fungus is abundant in many soils, and we do not know why it can lay dormant for many years before suddenly attacking an established tree. It is possible that stresses to the tree, such as a drought or living in poor soil, can make it more susceptible to this disease.
There are no treatments available to remove the fungus from the soil where it survives. Management relies on keeping trees in good vigor. Trees with recent wilt symptoms may be able to section off the infection themselves and recover.
Dead branches should be pruned out to prevent infection by other fungi and to improve the appearance of trees with chronic infections. Since the fungus lives in the soil, trees that have died from verticillium wilt should be replaced with resistant species. Thankfully there are many species of trees and shrubs that are unaffected by verticillium wilt.
Planted too deep: This is a non-infectious disease, but a problem that is increasingly common. The good news is that it can be addressed at planting time. No matter if it is maple, or any tree type, if you look at the trunk of the tree where it enters the ground and it looks like a utility pole going straight into the ground, it is planted too deep.
Instead, the tree trunk should flare or be wider as it enters the ground.
Trees planted too deep have roots that are buried down in the soil, and often oxygen decreases the deeper in the soil you go. Additionally, tree bark that should be exposed to the air above ground is instead surrounded by soil, causing additional issues that can result in more stress and can negatively affect the overall health of the tree.
Girdling Roots: Girdling roots can be a result of planting trees too deep, but can also be caused by roots growing in a circular pattern in the container or ball. These roots should be disturbed in such a way to encourage roots to grow out, rather than continue in the circular pattern. Girdling roots become problematic when they grow up against the main trunk, disturbing the vascular flow of water and nutrients up and down the tree. This often results in a declining canopy and branch dieback.
Addressing root issues prior to planting is a must. This girdling can occur above and below the soil surface. It you are concerned about this, hiring an arborist to take a look and recommend a plan of action is important. The size and age of the tree, the soil type, and the number of girdling roots should be considerations when developing a plan of action.
So, if you are seeing some maples not looking their best, it is important to diagnose the situation. Is it a leaf disease or diseases that may look bad, but are not very serious? Is it a fungal issue that is internal to the tree? Or is it a problem that is non-living, but rather a result of bad horticultural practices?
If you have a maple that is struggling and need additional assistance, contact a certified arborist. Information is also available by calling your local Extension office. In Lucas County, I would love to hear from you and learn more about what you are seeing in your own landscape or neighborhood.
Amy Stone is an extension educator with the Ohio State Extension — Lucas County, Agriculture and Natural Resources. Contact her at: stone.91@osu.edu.
First Published October 12, 2021, 12:00 p.m.
