The Japanese maple is a very sophisticated tree because of its unique leaf shape and other qualities. There are not many similar examples in the tree world at all. Today we will look at one of the frequent problems of this plant.
Root rot is a serious problem for the Japanese Maple and it may even die as a result. This disease often occurs due to overwatering the soil by frequent watering or improper tree placement.
Being constantly wet, the roots soften and begin to rot. At this time, the supply of water to the leaves is disrupted. Depending on the weather, the foliage may shrivel and turn brown. But if the weather is damp and overcast, the leaves will turn black or dark green.
How to fix it:
Avoid planting a maple in poorly drained soil or close to water sources (water from a roof, pond, stream). Also, avoid watering too often; maples need water when the soil is more than 1 inch dry.
If trouble occurs, eliminate all possible causes of overwatering. This means stopping watering too often and directing surface water away from the tree. If the sun is too strong, shade the maple a little.
If the maple survives root rot, transplant it to a less wet location to avoid a repeat of the disease. Do this early in the spring and use well-drained soil.
Late frost is another possible cause of the blackening of Japanese Maple leaves. In spring, there is often a significant drop in temperature, especially at night. If young leaves are already on the tree at this time, they may be severely affected.
The smallest and not yet fully unfolded leaves turn black first. While more mature leaves may not be affected at all. But a hard frost can even make the larger leaves watery and they will eventually turn black.
How to fix it:
To avoid frost damage, plant Japanese maple trees where there are no cold drafts. It will be better if the tree is protected by a building or fence on at least the north side.
Watch the weather forecast in the spring. If frost is coming, cover the maple with frost protection material. You can buy such material at almost any garden store. The main thing is for the material to let the air in. Never use plastic to cover maple trees.
If your Japanese Maple grows in a pot, move it to the garage for the frost.
Remove any damaged leaves from the tree. When the frost has passed, water the maple once with liquid fertilizer.
Too much sunlight always leaves a mark on the leaves. Among Japanese maples, yellow and variegated varieties are the most susceptible to sunburn. Newly planted maples can also suffer from too much light.
The first symptom of sunburn will be large white areas on the leaf. If the weather is dry and sunny, the spots on the leaves will dry out and turn crispy brown. But if the weather changes to cloudy and humid, the burns can turn very dark green or almost black.
How to fix it:
To avoid burns, check with your supplier about how much sunlight your maple can tolerate. Plant it strictly according to the supplier’s recommendations.
If burns occur, shade the maple on the hottest days using a garden umbrella or netting. Next spring, transplant to a semi-shady location.
If a newly planted maple is sunburned, shade it the first year for the summer. Also, don’t let the soil near the roots dry out more than 1 to 2 inches.
Remove any badly damaged leaves and water the tree with a multi-purpose liquid fertilizer.
Powdery mildew is a fungal disease that affects many plants, including Japanese Maple. It is one of the most common diseases among garden plants.
The pathogens of this disease settle on the leaves and multiply on them. Symptoms are blackening of the leaf plate and white powder on it.
Eventually, the leaves wither and fall off. If nothing is done, the disease will spread to all leaves and the tree may die.
Powdery mildew pathogens are most active in humid and warm weather. Weakened or damaged trees suffer most often. Improper care can also lead to this disease.
How to fix it:
Spray maple trees with a fungicide designed to control powdery mildew. Repeat the spraying after 2 to 3 weeks.
Avoid using neem oil as it can burn the foliage. Neem oil is good against powdery mildew but is contraindicated on Japanese maples.
Remove all dead and diseased leaves. Burn them or throw them away as far away from the yard as possible.
Provide good air exchange around the maple trees. If the tree is too dense, thin it out a bit.
Avoid planting Japon maple in a dark and damp place. It is better that it gets 4-6 hours of direct sunlight a day. Never overwater it.
Sooty Mold is a disease that causes Japanese maple leaves to turn black. This disease is the result of insect activity.
Aphids form colonies on the upper leaves of the tree and secrete a sticky substance during their lifetime. This substance falls on the lower leaves and twigs. Where the leaves are covered with sticky secretions, a black-colored fungus forms.
This can look different. Sometimes small, blurry spots appear on the leaves. But sometimes the entire leaf is covered with a black coating.
This disease rarely causes the tree to die, but when you consider the damage from aphids, the leaves can be severely affected.
How to fix it:
If you see black leaves at the bottom of the crown and there are aphids on the top leaves, it’s probably Sooty Mold. Remove any leaves that are heavily covered in black.
Rinse off the aphids and the lower leaves with a stream of water from the hose. Then spray the maple with insecticidal soap.
After a week, spray the entire crown with a multi-purpose fungicide or find a and use a specific product to control Sooty Mold.
Read more: How Do You Treat Fungus On A Japanese Maple?