Remedy of Japanese Maple Fungus On Trunk [Treatment Guide]

Japanese maples are very popular among gardeners for their beautiful leaves and striking colors. Therefore, most gardeners plant Japanese maples to enhance their garden’s beauty. However, a major problem with Japanese maples like other trees is the fungus on the trunk. There are two types of fungus that can affect Japanese maples on the trunk- black knot fungus, and canker.

Once a maple tree is infected with fungus, various problems can occur. So every gardener should have a clear idea about the symptoms and treatment of fungal attacks. That is why today I will discuss Japanese maple fungus on the trunk in detail. At the same time, I will tell you how to protect the tree from this problem very easily. So without delay let’s get started.

2 Proven Fixes For Japanese Maple Bark Fungus

1. Canker

There are several species of fungi that are responsible for causing canker on your Japanese maple tree. Canker is a problem where the fungus enters through a crack in the bark of your tree and spreads to destroy the entire bark. Even the disease causes the bark to crack and split, and can eventually lead to the death of your tree.

A common feature of all species of canker fungi is that they produce lesions on the bark.  However, by looking at these lesions, you can quickly identify which species of fungus has infected your Japanese maple tree. Here I discuss several types of fungi that cause cankers.

  • Nectria cinnabarina canker This species of fungus is often quite deadly.  Have you noticed pink or burnt brown lesions on the trunk of your Japanese maple? Then it is definitely Nectria cinnabarina canker. They especially attack the weak part of the bark of your tree. Sometimes they even appear as red balls and can confuse you.
  • Nectria galligena cankerThis species of fungus attacks the dormant stage of your Japanese Maple tree and kills the bark.  Take a good look at your tree in the spring, has the tree regrown a thin layer of bark on the infected area?  Then wait for some time.  If the bark dies back and the maple tree develops paper-like lesions, you can be sure that it is Nectria galligena canker.
  • Valsa cankerYou will find Nectria galligena canker similar to this species of fungal canker. As a result, you can easily get confused. Note the levels of canker in that case. They will be quite thick and not peel easily from the tree trunk. Also, if you remove the bark from the canker you will see a layer of visible, light-brown mushroom tissue.
  • Cryptosporiopsis cankerIf your Japanese maple tree is young, it is more likely to be affected by this fungus. As a result of their attack, a small long lesion is formed on the tree.  It looks like someone has pushed some bark off the tree. But as the tree grows, so will the lesions. But the most deadly thing is that you can also witness the bleeding in the center of the canker as the spring juice rises.
  • Bleeding cankerIf your Japanese maple tree looks wet and some of the bark is coming away from the trunk, especially lower down on the trunk, it is definitely an infestation.

Treatment Guide

Basically, canker disease is caused by different species of fungi, but its treatment is the same for all species. Since canker is a very deadly disease of Japanese maple, you should try to fix the tree by following the step-by-step guideline.

First, you need to find the affected area. Canker usually attacks the branches and stems of maple trees. So look for areas where the bark is cracked or dead. Once the affected parts are found, prepare to prune them now. Prune limbs to at least 1.5-2 inches below visible signs of canker. In this case, be sure to sterilize the pruning tools.

After pruning you need to apply the chemical treatment. A good quality fungicide is very effective against cankers. In this case, I would suggest you use a copper-based fungicide.  But before use must follow the manufacturer’s info. 

Above all, pay close attention to the health of the plant. Because healthy trees are less susceptible to diseases like cankers. Plant your maple tree in well-draining soil and water regularly. Avoid over-fertilizing and over-watering.

2. Black Knot Fungus

Black knot fungus disease is a well-known problem of Japanese maple trees. In fact, this disease is caused by the attack of a species of fungus called Apiosporina morbosa. They mainly attack tree branches.

The disease is not easily diagnosed so you need to be sure only if you see several symptoms. The first symptom to look for is swollen branches. If you pay close attention, you will see a swollen or knotty area appearing on your maple tree. These knots will initially be small and green. Later it will grow and turn black.

The affected branch will begin to die back within a few days and become completely leafless as the disease progresses. If you notice, you will see cankers in the knotty areas of your tree. Even when infected your plant will stop growing normally.

Treatment Guide

Pruning is the first way to rid Japanese maple of black knot fungus. Identify the affected parts of your plant and remove them. But if the disease is severe then you have to remove the entire branch. Pruning equipment must be sterilized to prevent it from infecting other plants. 

The final treatment is to use a good-quality fungicide. But the season is a major factor in this case. If you spray the fungicide in early spring, it will be more effective.

Frequently Asked Questions (FAQs)

What is the white fungus on my Japanese maple?

The white powdery coating on your Japanese maple leaves is a white fungus. It is also called powdery mildew. Basically wet and damp environment favors the attack of this fungus.

What is the best fungicide for maple trees?

Which fungicide is best for your fungus-infested Japanese maple depends on the severity of the disease and the species of fungus. However, copper-based fungicides are effective against any fungal attack.

What causes fungus on maple trees?

There are several reasons behind the fungal attack on maple trees. Waterlogging at the base of the tree is a major cause. Apart from this, factors like applying excess fertilizers, planting trees in poor soil, and applying water to trees from above also affect the attack of fungus.

Final Words

Japanese Maple Fungus on Trunk is a complex problem.  Because once the fungus attacks the tree, it comes back again and again.  As a result, the tree becomes weak internally and the growth of the tree is reduced. So be very careful about fungus. In this case, emphasis should be placed on prevention rather than cure.

By following some basic rules such as regular watering, ensuring well-drained soil for the plant, avoiding excessive fertilizer application, and not allowing water to accumulate in the root zone, you can easily protect your Japanese maple tree from fungus. If the plant is still affected by fungus, follow my guidelines in this article. Hope you can fix your tree quickly.

Happy Gardening. 

James Rivenburg
James Rivenburg
James Rivenburg

James Rivenburg is the founder of, a passionate gardener with valuable experience and knowledge gained through trial and error. The website has a large community of followers who trust his tips and techniques and have succeeded with his advice. He is always Committed to helping others create a beautiful and healthy garden.

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