Japanese maples, known for their vibrant foliage and elegant form, are a popular choice among garden enthusiasts and landscape designers alike.
However, like all living organisms, these trees are susceptible to various diseases and pests that can affect their health and aesthetic appeal.
Knowing what to look for and what to do when problems arise will help you confidently care for your prized landscape tree.
Want to give your trees the best care possible? Master the basics and expand your cherry tree knowledge with my detailed Japanese Maple Guide.
Japanese Maple Diseases
Japanese maples are generally hardy trees, but they can fall prey to several diseases. Understanding these diseases, their symptoms, and their treatment methods is crucial for maintaining the health of your tree.
Verticillium wilt is a soil-borne fungal disease that can cause serious harm to Japanese maples. It is characterized by the wilting, yellowing, and eventual browning of leaves, often on one side of the tree.
The disease can be difficult to control once it has infected a tree as the fungus can persist in the soil for many years.
Prevention: Ensure that your tree is planted in well-draining soil and is not overwatered as the fungus thrives in wet conditions. Regularly check your tree, and remove and dispose of any infected plant material immediately to prevent the fungus from spreading.
Treatment: Act quickly. Prune and dispose of infected branches to prevent the disease from spreading to the rest of the tree. In severe cases, a professional arborist may be needed.
Phytophthora Root Rot
Phytophthora root rot is a common disease in Japanese maples caused by a water mold that lives in the soil. Symptoms include yellowing leaves, stunted growth, and the eventual death of the tree if left untreated.
Prevention: Good drainage is key to preventing Phytophthora root rot. Avoid planting Japanese maples in areas where water tends to collect. Raised beds or mounds can also help improve drainage.
Treatment: If your tree is infected, reduce watering, and consider applying a fungicide specifically designed to treat Phytophthora. In severe cases, it may be necessary to remove and replace the affected soil, which is easier said than done.
Cankers are areas of dead bark on the trunk or branches of a tree, often caused by a fungal infection. They can cause branches to die back and can eventually kill the tree if they encircle the trunk.
Prevention: To prevent cankers, avoid injuring your tree as wounds can provide an entry point for the fungus. This includes avoiding unnecessary pruning and protecting the tree from lawn equipment.
Treatment: Prune and dispose of branches with cankers, making sure to disinfect your pruning tools between cuts. Fungicides are generally not effective against cankers.
Anthracnose is a fungal disease that causes dark, sunken lesions on leaves, stems, and flowers. It can lead to significant defoliation, often giving the tree a blighted appearance.
Prevention: Good sanitation practices can help prevent anthracnose. This includes raking and disposing of fallen leaves and pruning out dead wood.
Treatment: Fungicides can be effective if applied early in the disease cycle, typically in the spring when new leaves are emerging.
Phyllosticta Leaf Spot
Phyllosticta leaf spot is a fungal disease that causes small, round, brown spots on the leaves of the Japanese maple.
Prevention: Ensure your tree has good air circulation to reduce leaf wetness. Avoid overhead watering, which can spread the fungus.
Treatment: If your tree is infected, remove and dispose of fallen leaves and prune out infected branches. Fungicides can also be used if the infection is severe.
Pseudomonas Tip Blight
Pseudomonas tip blight is a bacterial disease that causes the tips of branches to turn brown and die back.
Prevention: Avoid pruning during wet or humid weather, which can help the bacteria spread.
Treatment: If your tree is infected, prune out the affected branches. Copper-based sprays (find it here) can also be used to control the disease.
Sooty mold is a type of fungus that grows on the honeydew excreted by certain pests. It doesn’t harm the tree directly but can block sunlight, which can affect photosynthesis.
Prevention: The best way to prevent sooty mold is to control the pests that produce honeydew.
Treatment: If your tree is affected, control the underlying pest problem. The sooty mold can then be washed off the leaves with a strong stream of water.
Japanese Maple Pests
While Japanese maples are relatively resistant to pests, they can still be affected by a variety of insects. Here are some of the most common pests you might encounter and how to deal with them.
Aphids are small, soft-bodied insects that can cause damage by sucking the sap from the leaves of your Japanese maple.
Prevention: Encourage beneficial insects, such as ladybugs and lacewings, which are natural predators of aphids.
Treatment: If your tree is infested, you can often control aphids by spraying the tree with a strong stream of water to knock them off. In severe cases, you may need to use an insecticidal soap or neem oil.
Mites are tiny arachnids that can cause damage similar to aphids. They are often hard to see without a magnifying glass, but their damage can be quite visible, often causing a stippled or bronzed appearance to the leaves.
Prevention: Like with aphids, beneficial insects can help control mite populations.
Treatment: Mites can often be controlled with insecticidal soaps or miticides.
In my guide for spider mites on Japanese maples, I go into detail on handling and preventing these annoying pests.
Scale insects are small, immobile insects that attach themselves to the stems and leaves of trees and suck the sap.
Prevention: Regularly inspect your tree for signs of scale. Prune and dispose of infested branches.
Treatment: Insecticidal soaps, horticultural oils, or systemic insecticides can be effective against scale.
Japanese beetles are a common pest that can cause significant defoliation. They are easily identifiable by their metallic blue-green bodies.
Prevention: Regularly inspect your tree during the summer months when these beetles are most active.
Treatment: Hand-picking can be effective for small infestations. For larger infestations, consider using a pheromone trap or an insecticide.
Mealybugs are small, white, cottony insects that suck the sap from the leaves and stems of your Japanese maple.
Prevention: Regularly inspect your tree for signs of mealybugs, and remove them promptly.
Treatment: Insecticidal soaps or neem oil can be effective against mealybugs.
Borers are insects that lay their eggs inside the bark of trees. The larvae then tunnel through the wood, causing significant damage.
Prevention: Keep your tree healthy as borers are more likely to infest stressed or injured trees.
Treatment: Infested branches should be pruned and destroyed. Insecticides can be used, but they are often not effective because the larvae are protected inside the tree.
Soil nematodes are microscopic worms that can damage the roots of your Japanese maple, leading to yellowing leaves and stunted growth.
Prevention: Ensure good drainage as nematodes thrive in wet soil.
Treatment: Nematodes can be difficult to control. In severe cases, it may be necessary to remove and replace the affected soil.
While ants themselves do not typically damage trees, they can farm aphids for their honeydew, protecting them from predators and leading to larger aphid populations.
Prevention: Control aphid populations to make your tree less attractive to ants.
Treatment: If ants are a problem, consider using ant baits or insecticidal sprays.
For a much more thorough explanation to deal with ants, check out my full guide to ants on Japanese maples.
While Japanese maples can be affected by a variety of diseases and pests, with proper care and attention, they can thrive in your landscape.
Regularly inspect your tree for signs of disease or pests, and take action at the first sign of trouble. Remember, a healthy tree is more capable of resisting disease and recovering from pest damage.