Japanese maples are prone to some pathogenic diseases that become a great problem for the growers if they are not careful about how to treat them. Sadly, a healthy maple tree can suddenly become very sick and stand on the verge of its death.
However, if you get the right picture of what disease is causing trouble in your Japanese maple tree, you can start the specific treatment for it.
The good news is, in this article, I am going to discuss 5 major diseases of your Japanese maple with every detail you need to know including how to identify, treat and prevent them as well.
So, let’s get down to business–
|Fungus in wet conditions
|Brown or black spots on leaves, cankers
|Remove infected branches, improve air circulation, fungicides
|Wilting, yellowing, and browning of leaves, dieback of branches
|Prune infected branches, improve soil drainage, reduce stress
|Fungus in humid conditions
|White, powdery coating on leaves and stems
|Improve air circulation, reduce humidity, fungicides
|Phytophthora Root Rot
|wet soil for a long period or poorly drained soil
|The leaves start wilting and drying
|the plant needs more nutrition to be able more strong against phytophthora root rot
|Fungi entering through wounds or stress
|Sunken, discolored areas on branches and trunk, dieback of branches
|Remove infected branches, improve tree health
5 Major Diseases Of Japanese Maple With Control Measure
1. Verticillium Wilt
Verticillium Wilt is a fungal disease that can attack Japanese maples. It attacks the plants from the roots and later spreads to the internal system of the plant. Also, It can turn out to be a very dangerous disease for your Japanese maple.
The thing is, this fungus mostly attacks weak and stressed plants after drought or frost. The main problem with this wilt is, it mimics the symptoms of environmental problems and after a spell of frost or drought it seems like the plant is suffering from these environmental issues rather than the fungal issue.
So, it becomes much harder to diagnose the disease at the right time. The way to protect your plant is by keeping an eye on it so that you can detect the verticillium wilt at its initial stage of an attack. In this way, the damage done to your Japanese maple will be the least.
Basically, It’s a soil-borne disease and sadly it cannot be prevented. The fungus mainly attacks when the soil is kept wet for a long time especially during early fall to late summer when the temperature is mild.
- Leaves of particular branches become discolored and die gradually
- The dead leaves droopily stay attached to the plant for some time then they drop off
- If you scratch the dead bark you will see the tissue underneath is brown and mushy ( the uninfected tissues will be green)
- Leaves will curl, turn yellow and eventually turn brown
- Stems and some branches die back
- The symptoms can even develop only on one side of the plant, the other side being completely unaffected
We don’t destroy any plant unnecessarily so rather than removing the Japanese maple we will focus on building its tolerance to verticillium wilt.
When you suspect this wilt, get the best fungicide for your tree and pour it on the soil. Choosing a good one is very important, otherwise, the wrong chemical formulation can hurt the Japanese maples. Don’t forget to follow the label directions properly (our pick)
Other than this, water the tree when the soil is dry and make sure the trees are shaded in the afternoon. In addition, fertilize the tree during the growing season and use a high phosphorus and low nitrogen-containing fertilizer made for shrubs and trees. ( our pick)
Prune the branches that are dying, along with the already dead ones at the first sign of the disease. Don’t worry, the plant will regrow new healthy branches to replace the diseased older ones.
You can get a more clear picture of the disease by watching the following video–
You see, the fungus dwells on soil and it’s very persistent. Once the soil has been infected, it’s best not to plant any trees there otherwise it will be infected too.
You can prevent this fungus by soil solarization. For this, dig the infected soil and then wet it with enough water. Now, cover the infected area with a clear plastic tarp and bury the ends under the soil up to 8 cm depth.
This clear plastic tarp will contain the heat within and turn the temperature higher inside. Keep it this way from 3 to 5 weeks under bright sunlight and the heat generated inside will kill the fungus.
Anthracnose is another fungal type of disease that attacks Japanese maples. This disease mostly attacks and becomes severe during the rainy season when the humidity is high.
The problem is, anthracnose fungus remains active on the fallen leaves and twigs that are kept on the ground. Whenever it’s convenient for them they release spores that spread through rainwater and infect healthy plants again.
- The leaves have spots that look like they are scorched
- Leaves and buds turn brown and eventually die
- Leaves and stems have dark and sunken lesions
- Young branches and twigs die back
- Young branches can become deformed and even killed
Since they survive in the debris, it’s best to take out the dead leaves and twigs from the ground as soon as possible, especially during the rainy season.
At the initial symptoms of anthracnose start using a copper-based fungicide on them for the most effective action. (our pick) Carefully read the instructions on the package and apply accordingly
In my experience, applying the first dose of copper fungicide just before the bud break stage during the spring season is much helpful in protecting the new growth from infection.
In the package see the minimum interval mentioned between two applications and according to that keep applying as long as the wet weather continues.
Collect the infected leaves and dispose of them. Preferably you can burn them or wrap them in and throw them away in the garbage bin.
Good thing is that, if you maintain good sanitation in the garden then you can prevent the incidence of anthracnose to a high extent. Let the tree free of excessive branches so that they can have ample air circulation and sunlight penetrating throughout the tree.
Make sure the tree is in well-drained soil that is also not waterlogged. And make sure to use organic compost in the soil. This added nutrition from the compost will help your Japanese maple to be more resistant to anthracnose.
While watering it’s best to use a drip sprinkler. You see, in this way the water will not wet the leaves and will just reach directly to the roots. As a result, the disease won’t be able to spread through wet leaves.
3. Powdery Mildew
Powdery Mildew is a very common fungal disease that can attack Japanese maples very often. This disease can be very easily detected because it covers the entire upper surface of the leaves with a white powdery film.
It occurs when the environment is hot and humid, especially during the late summer with drizzling rain when the temperature is between 15oC and 27oC. Poor air circulation also facilitates the fungus to spread more rapidly.
- The leaves have white patches of fungus on the lower surface
- In severe conditions, the patches get enlarged and cover the entire leaf surface
- The edges of the leaves start to curl upwards
- The leaf turns slightly purplish or reddish sometimes
- Very small and black pointy fungal structures are seen on the underside of the leaves
The best way to treat powdery mildew is to apply a sulfur-based fungicide at the earliest sign of the disease. (our pick) Apply according to the label direction and spray in all parts of the plant including both sides of the leaf.
You need to spray the fungicide once every week as long as the white powdery substance exists on your Japanese maple. However, remember to apply it during the cooler part of the day otherwise using a fungicide under hot weather can damage the plant tissues.
You can wash the foliage every once in a while with a hose to wash off the powdery growth but be sure to do this during the morning so that the leaves will be dry before sunset.
You can try some homemade fungicide recipes for efficiently treating the powdery mildew on your Japanese maple. The recipes are given below–
- Baking Soda Recipe
- A tablespoon of baking soda
- A teaspoon of liquid dish soap
- 5 liters of water
- Mix all the ingredients and transfer the mixture into a spray bottle
- Spray on the underside of the leaves and other areas with powdery growth
- You can use this both to control and prevent the powdery mildew on your Japanese maple
Note: before using any homemade fungicides, try it on a small area to see if the formula suits your Japanese maple. If not, try diluting the solution with water.
The thing is, powdery mildew loves to attack the soft tissues so you have to be a bit careful when the Japanese maples are young. It can spread through leaves and debris so you have to keep the garden free of them by raking up.
However, don’t put the fallen infected leaves on the compost pile as they can overwinter there and attack when applied to the plant as compost.
You can cut off a few branches along with severely diseased ones to improve air circulation. And don’t forget to sterilize the garden shears before giving any cut because they can be contaminated by the fungal spores from any other place.
4. Phytophthora Root Rot
Phytophthora root rot occurs when the soil is wet for a long period or the soil is poorly drained. Since the Japanese maples cannot tolerate the wet soil condition for too long, they are more susceptible to this disease.
This is one of the most troublesome issues of Japanese maples if they are planted too deeply in the ground. Because it causes the roots to be stuck within the compact soil layer and causes suffocation.
Once the phytophthora gets inside the root system it follows the water-conducting tissues and moves upward the plant. Eventually infecting the stems and leaves and killing the Japanese maple.
- The leaves start wilting and drying
- Leaves turn dull greenish to yellow like chlorosis and sometimes red
- The young tree can be easily killed
- A kind of dark sap can ooze out from the damaged stems
- If the tissue underneath the bark is cut reddish-brown streaks are seen
- The lower trunk blackens and the shoots die back
- Roots become brown and soft
This disease produces spores that are easily spread by water and gardening tools. The thing is, this disease can be treated but cannot be prevented very easily without being very cautious.
When you have confirmed its presence isolate the plant from other uninfected ones to prevent it from spreading. If the tree is big enough then shifting is probably not the best option but if they are much younger then you can shift it to another location in soil with better drainage.
To kill the phytophthora pathogens very effectively apply a 3% household hydrogen peroxide solution in the soil. (our pick) Mix three parts of water with 1 part of hydrogen peroxide and pour it around the tree. However, handle the product very cautiously as per the package instructions.
Take necessary actions to improve the drainage of the soil otherwise, the infection can come a few weeks later. If your tree is in clay soil then there are more frequent chances of infection and to avoid this, you can add some loamy soil and replace the clay soil with it.
Getting your plant enough nutrients will keep them healthy and then they’ll be naturally able to be more strong against phytophthora root rot. So, provide your Japanese maple with the best kind of tree fertilizer during the growing season (our pick)
Besides, when any plant or plant parts are infected, dispose of them carefully. Remember to never put them in a compost pile or mix them in the mulching materials. Otherwise, the disease will keep spreading through these.
Weeds often carry many pathogenic diseases so make sure you keep your garden weed free as much as possible. After working in the garden, always clean the garden equipment with one part bleach mixed with four parts of water.
5. Bacterial Canker
Bacterial canker is a very common disease for Japanese maple trees along with some other fruit trees like cherries, apricots, plums etc. Normally, the bacteria usually enter through any wounds present in the tree. It can be either any place from where a branch is cut off or any other injury during the pruning.
In addition, frost damage after the winter is over can cause more damage by influencing more bacterial infections. You see, bacterial canker can infect your Japanese maple during any cool and wet weather in any season like fall, spring or winter.
This disease is very infectious because the bacteria overwinters and later infects the growing young buds of the trees. Also, it spreads very fast with rain, water and garden equipment.
- The twigs and bark has sunken water soaked lesions
- The lesions also secrete a sour-smelling gummy substance
- The color of the wounded area becomes darker than the healthy parts of the bark
- The tissue underneath the lesion is moist and reddish brown or black in color
- Besides, the leaves start to have spots, turn yellow and curl
- The leaf veins get blackened
- The growth of the tree is stopped
Sadly chemical control isn’t very effective against bacterial cankers. However, copper fungicides have shown some success against it. You can try the following recipe to make your own homemade copper fungicide
#Recipe: Copper Fungicide Recipe
- 2 liters of water
- 30 ml of copper sulfate
- 4 tablespoons of Calcium hydroxide (also known as hydrated lime)
- Take a plastic bucket and mix water and hydrated lime
- Use a plastic spoon to stir the solution slowly
- Remember to prevent using any metal objects because metals can react badly with the ingredients
- Now you have added the copper sulfate while stirring the mixture continuously otherwise it will not mix well
- Now put the solution in a plastic sprayer and spray it on the infected areas of your Japanese maple
- While spraying, give the solution a good shake once in a while
- Spray it twice a week thoroughly
- Don’t store the leftover solution
- After spraying, empty the spray can and wash it very thoroughly
Since chemical methods aren’t always responsive, you have to take enough preventive action to save your Japanese maple from death due to bacterial canker. Keep the bark area dry and get rid of the weeds from around the base of the Japanese maple.
Make sure you prune the tree during the late spring season when their growth is steady so that they can heal the wounds faster. And avoid pruning during winter and fall when the bacteria are most active. Also, avoid damaging the main trunk as much as possible while pruning.
While pruning make sure you disinfect the garden tools with rubbing alcohol or bleach solution beforehand and after pruning treat the cut areas with a pruning sealer (our pick)
Treating your Japanese maple with the correct measures is very important otherwise no matter how hard you try it will be too late. Also, wrong treatments can cause more serious damage than the disease itself.
So, the best way is to prevent the disease from happening with some easy measures and figure out the issue by matching it with the symptoms then start treating the disease. I hope this article was a great help to you in taking control of the diseases in your Japanese maple.
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