Maple Tree Bark Disease – Diseases On Maple Trunk And Bark


There are many kinds of maple tree diseases, but the ones that people are most commonly concerned with affect the trunk and bark of maple trees. This is because bark diseases of maple trees are very visible to a tree’s owner and can often bring about dramatic changes to the tree. Below you will find a list of diseases that affect maple trunk and bark.

Maple Tree Bark Diseases and Damage

Canker Fungus Maple Tree Bark Disease

Several different kinds of fungi will cause cankers on a maple tree. These fungus are the most common maple bark diseases. They all have the same thing in common, which is that they will create lesions (also called cankers) in the bark but these lesions will look different depending on the canker fungus that is affecting the maple bark.

Nectria cinnabarina canker – This maple tree disease can be identified by its pink and black cankers on the bark and typically affects parts of the trunk that were weak or dead. These cankers can become slimy after rain or dew. Occasionally, this fungus will also appear as red balls on the bark of the maple tree.

Nectria galligena canker – This maple bark disease will attack the tree while it is dormant and will kill healthy bark. In the spring, the maple tree will regrow a slightly thicker layer of bark over the fungus infected area and then, the following dormant season, the fungus will once again kill back the bark. Over time, the maple tree will develop a canker that looks like a stack of paper that has been split and peeled back.

Eutypella canker – The cankers of this maple tree fungus looks similar to Nectria galligena canker but the layers on the canker will normally be thicker and will not peel away from the tree trunk easily. Also, if the bark is removed from the canker, there will be a layer of visible, light brown mushroom tissue.

Valsa canker – This disease of maple trunks will normally affect only young trees or small branches. The cankers of this fungus will look like small shallow depressions on the bark with warts in the center of each and will be white or grey.

Steganosporium canker – This maple tree bark disease will create a brittle, black layer over the bark of the tree. It only affects bark that has been damaged by other issues or maple diseases.

Cryptosporiopsis canker – The cankers from this fungus will affect young trees and starts out as a small elongated canker that looks as though someone pushed some of the bark into the tree. As the tree grows, the canker will continue to grow. Often, the center of the canker will bleed during the rising of spring sap.

Bleeding canker – This maple tree disease causes the bark to appear wet and is often accompanied by some bark coming away from the maple tree trunk, especially lower down on the trunk of the tree.

Basal canker – This maple fungus attacks the base of the tree and rots away the bark and wood beneath. This fungus looks very similar to a maple tree root disease called collar rot, but with collar rot, the bark typically does not fall away from the base of the tree.

Galls and Burls

It is not uncommon for maple trees to develop growths called galls or burls on their trunks. These growths often look like large warts on the side of the maple tree and can get to massive sizes. Though often alarming to see, galls and burls will not harm a tree. That being said, these growths do weaken the trunk of the tree and can make the tree more susceptible to falling during wind storms.

Environmental Damage to Maple Bark

While not technically a maple tree disease, there are several weather and environment related bark damages that can happen and may look like the tree has a disease.

Sunscald – Sunscald most frequently occurs on young maple trees but can happen on older maple trees that have thin skin. It will appear as a long discolored or even barkless stretches on the trunk of the maple tree and sometimes the bark will be cracked. The damage will be on the southwest side of the tree.

Frost cracks – Similar to sunscald, the southern side of the tree cracks, sometimes deep cracks will appear in the trunk. These frost cracks will most commonly happen in late winter or spring.

Over mulching – Poor mulching practices can cause the bark around the base of the tree to crack and fall off.


Insect Pests

Woolly alder aphid (Paraprociphilus tessellatus).
Bob Lepak, Bugwood.org

Aphids: Aphids are soft-bodied insects that range from 1 /16 to ⅜ inch long. They may be green, yellowish, pink, gray, or black. They feed by piercing plant tissue and sucking plant sap. They prefer feeding on new growth in such areas as shoots, buds, and the undersides of leaves. As they feed on plant sap, they excrete honeydew (a sugary waste material). The sooty mold fungus grows on the honeydew, resulting in unsightly, dark fungal growth.

Woolly alder aphid (Paraprociphilus tessellatus) is gray to black in color. It gets its name from the fluffy, white wax found on its abdomen. It requires alder and silver maple to complete its life cycle. Occasionally, it is found on red maple. Colonies of these pests are obvious because of their white, fuzzy appearance. They are usually seen on leaves, twigs, or bark. Although infested leaves shrivel and drop early, the pests cause little permanent damage. As a result of the honeydew, sidewalks and cars become sticky.

Prevention & Treatment: Several natural enemies, such as ladybird beetles (ladybugs) and lacewings, feed on aphids. These predators should be allowed to reduce aphid populations as much as possible. Controlling this pest on a large tree using chemicals is expensive and often not practical. Since little permanent damage results from woolly alder aphids, tolerating some damage is a good choice. As a result of their phenomenal ability to reproduce, aphids are very difficult to control with insecticides. Leaving one aphid alive can result in the production of a new colony very quickly. In addition, the use of insecticides kills the beneficial insects that normally keep aphid populations under control.

However, if natural predators do not reduce aphid populations sufficiently, the following foliar spray insecticides are recommended: cyfluthrin, cyhalothrin, permethrin, bifenthrin, pyrethrin, and neem oil. Treat when aphids appear and repeat at seven- to 10-day intervals if needed. As an alternative, dinotefuran or imidacloprid can be applied as a drench around the root zone of aphid-infested plants and is systemically taken up by the root system for insect control (see Table 1 for specific products). As with all pesticides, read and follow all label directions and precautions.

Cottony maple leaf scale adults (Pulvinaria acericola).
Photos by Nancy Gregory, University of Delaware

Scale: Many scale species, including Pulvinaria acericola, Pulvinaria innumerabilis, and Melanaspis tenebricosa, are pests of maples. Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex, and species. Some are flat and appear like scales stuck to a plant, while others appear like white cottony masses. They feed on sap by piercing and sucking the leaf, stem, or branch with their mouthparts. Their feeding can weaken or kill branches. Heavily-infested trees are stunted with small flowers and leaves. Leaves may turn yellow and drop early.

Like aphids, soft scales, such as Pulvinaria species, also excrete honeydew. The growth of the sooty mold fungus on the honeydew results in leaves that are dark grayish-black. Armored scales, such as Melanaspis tenebricosa, do not excrete honeydew, as they feed differently than the soft scales.

Prevention & Treatment: A combination of various natural enemies, including ladybird beetles (ladybugs) and parasitic wasps, usually keeps scales under control. On small trees with light infestations, scales can be scraped off, or the infested branches can be removed and destroyed. On a large tree, it is not always practical to control scale chemically. The size of the tree, the need for specialized equipment, and the cost may prohibit this approach. Adult scales are relatively protected from insecticides by their waxy covering. Their immature forms, called crawlers, are susceptible, however. If it is determined that chemical control is necessary, the recommended chemicals include the following: cyfluthrin, cyhalothrin, bifenthrin, or permethrin. Apply materials when crawlers appear and repeat in 10 days. Both soft and armored scales can be controlled by a soil drench with dinotefuran. Soil drench applications are best made in the spring as new plant growth appears. See Table 1 for specific products. As with all pesticides, read and follow all label instructions and precautions.

Ocellate gall midge (Acericecis ocellaris).
Photo by Lacy L. Hyche

Gall Makers: Maples often develop irregular growths or swellings known as galls on their leaves. Gall development is a reaction by the leaf tissue to feeding or egg-laying by various mites (such as Vasates quadripedes and Vasates aceriscrumena) and insects (such as Acericecis ocellaris and Cecidomyia ocellaris). Galls vary greatly in appearance, from wart-like bumps to spindle-shaped protrusions to felt-like patches on the leaf’s surface. Each insect or mite produces its own distinctive gall shape. Often the distinctive shape allows for the identification of the pest. Galls typically develop in spring at about the time that leaves are expanding. Once the gall forms, the pest is protected inside the structure. When homeowners see these growths on the leaves of their maples, they often become quite concerned. It is important to remember that while unsightly, they do not cause permanent injury to a tree.

Prevention & Treatment: Since leaf galls do little, if any, long-term damage to the tree, control efforts are typically not needed or recommended. If a tree is small, the homeowner can handpick and destroy leaves before exit holes form to allow the release of the pest.

Granulate ambrosia beetle (Xylosandrus crassiusculus) larvae.
Photo by Will Hudson, University of Georgia

Asian Ambrosia Beetles: Japanese maples are among the more common hosts of the granulate ambrosia beetle (Xylosandrus crassiusculus), with other hosts including styrax, ornamental cherry (especially Yoshino), pecan, peach, plum, dogwood, persimmon, sweetgum, magnolia, fig, Chinese elm, and azalea. This pest is attracted not only to damaged, stressed, or transplanted trees but to seemingly healthy trees as well. The beetle becomes active in early March (or earlier), and the female beetles bore into trunks or branch wood of thin-barked hardwood trees. Once a tree has been attacked, it becomes more attractive to further attack. Often these trees are less than four inches in diameter.

Granulate ambrosia beetle (Xylosandrus crassiusculus) frass protruding from bark.
G.Keith Douce, University of Georgia, Bugwwod.org

Visible symptoms include wilted foliage, as well as the toothpick-like strands of boring dust (frass) that protrude from these small, pencil-lead size holes. The Asian ambrosia beetle does not feed upon the host’s wood but instead carries with it an ambrosia fungus, which grows within the galleries made by the beetle. This fungus serves as a source of food and may partially be responsible for the death of the host plant.

Prevention & Treatment: Heavily infested plants should be removed. If only a few branches are infested, they may be cut out. The life cycle takes approximately 55 days until the emergence of the next generation of beetles, so prompt removal or burning of the wood is important. Protective sprays on other susceptible plants may reduce their spread. Permethrin may be used as a trunk and scaffold limb spray beginning in March (see Table 1 for specific products). Thoroughly wet the bark. Multiple treatments may be needed during a season. Research indicates that spraying the infested trunks with permethrin may cause the beetles to leave the galleries they have already created. Since the beetles do not consume the host plant material, dinotefuran and imidacloprid systemic soil treatments are ineffective.


There are many kinds of maple tree diseases, but the ones that people are most commonly concerned with affect the trunk and bark of maple trees. This is because bark diseases of maple trees are very visible to a tree’s owner and are often bring about dramatic changes to the tree. Below you will find a list of diseases that affect maple trunk and bark.

Canker Fungus Maple Tree Bark Disease

Several different kinds of fungi will cause cankers on a maple tree. These fungus are the most common maple bark diseases. They all have the same thing in common, which is that they will create lesions (also called cankers [1]) in the bark but these lesions will look different depending on the canker fungus that is affecting the maple bark.

Nectria cinnabarina canker – This maple tree disease can be identified by its pink and black cankers on the bark and typically affects parts of the trunk that were weak or dead. These cankers can become slimy after rain or dew. Occasionally, this fungus will also appear as red balls on the bark of the maple tree.

Nectria galligena canker – This maple bark disease will attack the tree while it is dormant and will kill healthy bark. In the spring, the maple tree will regrow a slightly thicker layer of bark over the fungus infected area and then, the following dormant season, the fungus will once again kill back the bark. Over time, the maple tree will develop a canker that looks like a stack of paper that has been split and peeled back.

Eutypella canker – The cankers of this maple tree fungus looks similar to Nectria galligena canker but the layers on the canker will normally be thicker and will not peel away from the tree trunk easily. Also, if the bark is removed from the canker, there will be a layer of visible, light brown mushroom tissue.

Valsa canker – This disease of maple trunks will normally affect only young trees or small branches. The cankers of this fungus will look like small shallow depressions on the bark with warts in the center of each and will be white or grey.

Steganosporium canker – This maple tree bark disease will create a brittle, black layer over the bark of the tree. It only affects bark that has been damaged by other issues or maple diseases.

Cryptosporiopsis canker – The cankers from this fungus will affect young trees and starts out as a small elongated canker the looks as though someone pushed some of the bark into the tree. As the tree grows, the canker will continue to grow. Often, the center of the canker will bleed during the rising of spring sap.

Bleeding canker – This maple tree disease causes the bark to appear wet and is often accompanied by some bark coming away from the maple tree trunk, especially lower down on the trunk of the tree.

Basal canker – This maple fungus attacks the base of the tree and rots away the bark and wood beneath. This fungus looks very similar to a maple tree root disease called collar rot, but with collar rot, the bark typically does not fall away from the base of the tree.


What causes maple tree bark to split?

Q: Over the last couple of years, our Norway and Sunset maples have developed long, vertical splits in the bark. These splits can be as much as four feet long. This spring, some of them have been weeping. The problem does not seem to affect our other maples. Other trees are nearby but do not compete with these maples. One Sunset maple is on the west, the other on the east. The two Norways are on the north side. Do you have any idea as to what the problem is and how we can prevent further splitting as well as what to do with the existing splits?

A: The problem of bark splitting on maples is a common one, especially in this part of the country. The short answer is the splits will not likely cause harm, but let's go in detail.
Maples (Acer) as well as oaks (Quercus), linden (Tilia) and crabapple (Malus) trees we grow in Michigan are all susceptible to bark splitting. This is typically know as frost cracks in which longitudinal cracks develop on the trunk of trees facing south or southeast.

Generally, all types of maples (of which there are more than 40) are subject to cracking. And I believe reader Faubion has two types of maples in question here - Norway maple, or Acer platanoides and Red maple - of which "Sunset" is a hybrid, or Acer rubrum.

My research and experience shows that Norway maples are especially prone to frost cracks. This is also the maple that as it matures, migrate its roots to the soil's surface, causing all sorts of problems for sidewalks, driveways, mowing and grass.

This alone - especially in a city lot landscaping situation - is enough for me to not plant Norway maples. One reason folks like Norway is their foliage color - a rich green in summer and dependably, very yellow in the fall. Fall color often lingers well into late October when most trees are barren.

Frost cracks, as you might suspect, develop as bark and wood expand, then contract, in response to periods of wide temperature change. Think about it - maples tend to have dark bark so they absorb and hold the sun's heat - so the temperature on the bark on a sunny day in February may be relatively toasty, only to plummet after sunset.

This fluctuation sets up stress movement, especially in areas where the bark or older wood is already weak or cracked, perhaps from disease or mechanical damage. If the crack is severe enough, you can hear the wood splitting.

Fortunately, these cracks usually heal over, entirely or partly, in the following growing season.

That they would weep sap is understandable, as the normal flow has been interrupted by the injury. Maples tend to be "weepers" anyhow - how else would we get our Maple syrup and candy?

I would think that subsequent winters would not bring subsequent splitting, at least of the magnitude of year #1. In other words, I don't think you need worry about the tree cracking all around or so severely that it topples over.

None of the maples on my property have developed cracks, if they had and the crack was still fairly open at this point in the summer, I'd wrap it with tree wrap to protect it from insects and disease. Painting of tree wounds is no longer recommended the current thinking is fresh air is better than a glob of tar.

You can also protect existing cracks from possible further damage by wrapping the suspect area over winter with tree wrap. This is the brown corrugated stuff about two inches wide that is used much like an Ace bandage.

It is possible that a large crack fails to heal after a year or two and then it's time to do something. Arborists sometimes install a bolt or rod-like screw into the tree to secure the wood around the wood. Please, please, consult a professional for this analysis and remedy, if needed. Don't trust it or your tree to someone who simply cuts down or prunes trees on the side. The International Society of Arboriculture offers a free referral service at its website, www.isa-arbor.com.

Note to readers: if you purchase something through one of our affiliate links we may earn a commission.


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Red Maple Trees: Common problems

Red maple trees are popular but suffer from a number of problems. They are slow to establish, have poor branching structure and, most importantly, they are susceptible to long-term trunk injury or damage, which results in internal rot and decay. Because of these problems, they are not the best choice for a long-term shade tree in the Kansas City area.

Other, less serious problems can also plague these trees. A foliar disease called anthracnose can be hard on these trees. This disease is most severe under cooler and moist spring conditions. The leaf disease results in black spots covering the leaves. The infected leaf drops from the tree, leaving a thin canopy, which reduces the energy available to the tree for proper growth. Control of anthracnose is not recommended as it is not serious but does cause concern and leaves the tree looking less desirable. This disease happens almost every year depending on weather patterns.

Another alarming concern with red maples in the spring is tip dieback. The new growth that emerges in the spring can be killed back, turning a blackened color. This growth will eventually drop from the tree. The problem is referred to as scorch. Scorch occurs when the plant loses more moisture through the leaf tissue than can be supplied by the root and vascular system, such as during periods of prolonged drought.

If you have a red maple in the landscape, what can you do? The easiest answer is to provide good care. Avoid stress on the tree that would lead to trunk injury and prune properly to improve the branch structure. In addition, young red maples less then five years old should be watered on a regular basis throughout dry periods. The younger the tree, the more often. More established trees should be deeply soaked on a monthly basis.

When selecting a new shade tree for the landscape, do not settle for the easy and over-planted red maple. There are many other species of shade trees available with fewer problems that will provide beauty in the landscape.

Have questions? The Garden Hotline is staffed by trained EMG volunteers and Extension staff who will assist you with questions.


Watch the video: Qu0026A Why does my Japanese maple have brown curled leaves?


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