Japanese Maple Diseases

Japanese Maple Diseases

Japanese maples (Acer palmatum) are appealing trees creating green foliage that changes to vibrant hues of red purple, yellow and bronze. They develop in U.S. Department of Agriculture plant hardiness zones 5 through 8. According to the Clemson University Cooperative Extension, Japanese maples are susceptible to various diseases such as powdery mildew, anthracnose, leaf spot and root rot. Once it is possible to identify the disease attacking the Japanese maple, you also can take the required actions to control and keep it from returning.

Powdery Mildew

As its name implies, powdery mildew appears as a powder-like growth on leaves, stems and bows. It causes leaves to twist, curl and distort. Powdery mildew is caused by a fungus that spreads quickly and does not require moisture to develop. It’s prevalent in reasonable temperatures and nesting areas. Neem and olive oil are just two fungicides which may help control the powdery mildew assaulting the Japanese maple. In addition to fungicide application, keep the ground near the tree free of organic litter to protect against the spread of the fungal disease.


Black, tar-like spots appearing on the leaves is a sure sign the Japanese maple is infected with anthracnose. This fungal disease results in distorted foliage, stem dieback, cankers and finally girdling. Anthracnose occurs when conditions are humid and moist, and there’s no chemical treatment available. Luckily, prevention will reduce the possibility of the fungus causing anthracnose assaulting the Japanese maple. When you spot damaged or diseased branches, then remove and destroy them immediately. In addition, apply a preventive fungicide spray to the Japanese maple in bud break.

Leaf Areas

Leaf spot disease is the end result of one of several bacterial strains which attack plants. It typically presents itself as irregular-shaped, discolored patches or spots on the leaves. The infected leaves can fall from the tree in severe infestations. Leaf spot disease rarely causes serious damage unless the Japanese maple is all ready diseased or damaged. Removing the plant litter from the ground around and underneath the Japanese maple will keep this annoying fungal disease at bay.

Root Rot

Rots are brought on by the fungal pathogen phytophthora that attacks roots, collar and crown of the Japanese maple. Trees infected with this disease may have wilted, discolored and stunted leaves that drop from the tree. Cankers and vertical discolorations that seep black or red sap will develop on the back. Rots also cause stunted growth, branch dieback and decline, as well as the Japanese maple might finally succumb to the disease. Controlling root rot requires proper site preparation before planting and great irrigation.

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