Japanese Maple

• Japanese maple (Acer palmatum) trees -- with "lacy" green or dark red leaves -- grow about 12 inches per year and can reach up to 25 feet tall, although many are much shorter. The deciduous tree produces autumn colors of red, orange, copper and yellow. There are hundreds of Japanese maple cultivars adaptable to both shade and sun; they grow best in well-drained soil and do not need constant pruning.
  
  

Powdery Mildew and Armillaria

• Powdery mildew develops on maple leaves in winter. The dormant spores waken in spring and by summer, they turn into a white-light gray coating. Tiny black orbs may appear in the white powdery fungus, but the spots are a minor, secondary phase of the mildew. Armillaria is a group of fungi that affects the roots through a process called "shoestring root rot." Armillaria produces a soft, white layer between the bark and trunk wood that affects foliage with white "fans" of spores that spread into the roots.
  
  

Shoestring Root Rot Damage

• Plants severely affected by shoestring root rot cannot be saved. There is no cure or fungicide available, thus trees and shrubs should be removed as soon as possible so that spores do not spread to neighboring plants. Destroy the tree, its entire root system and, if possible, remove other plants from the contaminated soil that may already be affected. Do not plant new trees or shrubbery in that soil; armillaria can live for years, feeding from roots and stumps. Trees, plants and shrubs that are only slightly damaged by armillaria may be saved. Cut the diseased portions of the plant from the tree and remove the soil from the trunk and roots. Expose the roots to sunlight in the summer, but cover them before the first frost of autumn. Fertilize and water the plant, but do not hydrate the exposed root system. Soil may be "cleaned" through fumigation; contact a licensed pesticide company or your county extension service for more information.
  
  

Powdery Mildew

• Powdery mildew is a white, grayish fungus that affects plants, shrubs and a variety of trees, including Japanese maples. The fungus grows in spots and patches that are seen mostly on the tops sides of leaves but can also affect buds, fruits and young stems. It thrives in hot, dry climates, but high humidity helps spores to germinate. Powdery mildew grows in areas that have poor air circulation. Although many newer plant cultivars are resistant to the fungus, older plants in shaded areas with poor soil drainage are susceptible to the mildew. Fungicide mixtures of sulfur, triforine, potassium bicarbonate and neem oil may control the disease. Remove and destroy plants that are severely damaged. Do not compost the leftover plant materials.
  
  

Other Tree Diseases

• Anthracnose affects maple trees with various shapes of spores that congregate on leaves. Gray mold and "bull's-eye spot" are rounded lesions with tan-colored centers and darker edges. Cool, wet spring weather helps to produce multiplying fungal spores throughout the summer. Phyllosticta spot, also known as purple eye, has tan-colored centers with reddish brown edges. Tar spot fungus is a series of dark masses surrounded by yellow rings; the infection appears in the spring although the splotches do not appear until summer. Leaf blister comes from fungi that produce extra leaf cells that are larger than normal. Scorch -- light brown areas between veins -- occurs in high temperatures when trees do not have adequate water.