Japanese maple trees are susceptible to diseases such as anthracnose, verticillium wilt, tar spot, leaf spot, leaf scorch and root rot. Some of these diseases are potentially deadly, while others are usually harmless and merely cosmetic.
Verticillium wilt is one of the most dangerous Japanese maple diseases. It is caused by a soil-dwelling fungus that is very difficult to eradicate. The fungus attacks the tree through its roots, sometimes affecting one side of the tree while leaving the other intact. Verticillium wilt inhibits water flow while producing toxins. Leaves with brown margins grow smaller than normal, then wilt and drop off. Eventually the tree dies. Some trees recover when affected limbs are pruned. The best way to prevent the disease is to test the soil for the fungus before planting in the area.
Anthracnose first displays as brown spots on the leaves. Eventually the tree develops cankers on its branches and trunk. These are dead areas that surround the tree and sometimes kill it. Anthracnose is also caused by a fungus, but raking away damaged leaves, fertilizing, watering and applying fungicide are effective steps in helping the tree recover.
Root rot causes discolored leaves, cankers and stunted growth and can eventually be deadly. Tar spot, leaf spot and leaf scorch are all diseases that affect the appearance of the leaves but are not otherwise harmful to the tree. Raking away fallen leaves and spraying with fungicides help to control these diseases.