Verticillium Wilt

• Verticillium wilt begins as root infection caused by a fungus and spreads throughout the vascular system of the Japanese maple. Leaf wilting is the earliest and most common symptom, and if left unchecked, individual branches or even the entire tree may die. Proper watering may help trees recover or may prevent this disease entirely. Remove dead or weak branches, and make sure that the soil is high in potassium and low in nitrogen for best results. The fungus will remain present in the soil even after the tree dies, so when replanting, select trees that are not susceptible to this disease.
  
  

Phytophthora Root Rot

• Phytophthora root rot is caused by a particular type of water mold that is present in standing water. Trees that are located in an area that has been flooded are particularly vulnerable to this disease. Infected trees will have lesions as well as yellow leaves. Japanese maples that are infected with Phytophthora root rot will likely die, though some will hang on for several years before succumbing to the disease.
  
  

Leaf Diseases

• Several leaf diseases are common with the Japanese maple. According to the Bartlett Tree Research Laboratories, the most common are anthracnose, Phyllosticta leaf spot and Pseudomonas tip blight. These diseases are all caused by fungi. Typically, spores spread in windy conditions and propagate during cold, wet weather. Spots on leaves will be present and will be brown, purple or black. Some leaves may fall off prematurely. Most of the time, these leaf diseases will not kill the tree, and infection may last for only one summer. Leaf diseases may be prevented by fungicide, applied to the tree when in bud.
  
  

Insects

• Several insects attack the Japanese maple, but the Japanese beetle is the most common. These beetles feed on the leaves of the tree and can weaken it. Insecticide will rid the tree of beetles, but they may also be hand-picked off the leaves if the infestation is small.
  
  

Avoiding Disease

• The best way to avoid disease in the Japanese maple is to make sure that it gets sufficient water, especially during very hot weather. Do not overwater. Proper pruning will also help protect against disease.