The Japanese maple is native to Japan, China and Korea. A variety of cultivars are available, with heights ranging from 6 to 50 feet. The Japanese maple is a fast-growing tree that does well in well-drained highly organic soil, and light shade. For the most part the Japanese maple is easy to grow, but it is susceptible to several diseases. Some diseases are cosmetic in nature, and are not a major threat to the tree, while other diseases can be more severe.
Tar Spot and Sooty Mold
Tar spot and sooty mold are cosmetic in nature and do not affect the health of the tree. Tar spot appears as black spots on the leaves; a fungus causes the black spots. If aphids infest your tree, they will leave honeydew, which sooty mold thrives on.
Signs of anthracnose, a fungal disease are moist, sunken spots on the leaves. Eventually, the leaves will curl and foliage may be lost. This fungus usually appears after a severely cold/wet winter season. Repeated bouts of anthracnose will weaken the tree, leaving it susceptible to more serious disease.
Untreated anthracnose may lead to cankers, dead areas on a branch or the trunk. Cankers form when fungi enter the tree at a weak spot/wound. Once they enter the wound, they continue to spread. Cankers can kill a Japanese maple. Limbs infected with cankers can be removed, but nothing will save the tree if a canker encircles the trunk.
Maple wilt is quite serious--it can destroy your tree. This is also a fungal disease, and is caused by a soil fungus known as verticillium. Verticillium enters the tree through its roots, and continues up through its limbs. Signs of maple wilt are brown leaves and bare or diseased branches.
Maple Wilt Treatment
Removal of diseased branches is the only treatment, although most trees do not survive maple wilt--they are usually dead within a year.