Chinese Maple Diseases

Chinese maples are hardy but are susceptible to a few fungal problems.

The Chinese maple (Acer palmatum) is a woody plant native to China, Japan, Korea and southeast Russia. They are used in landscaping throughout U.S. Department of Agriculture plant hardiness zones 7, 8 and 9 and thrive in areas with full sun exposure and moderate temperatures. The tree produces shiny green foliage that turns red in the fall. It does well in a number of growing conditions and is generally hardy, but is susceptible to a number of diseases, some more common than others.

Tar Spot and Sooty Mold

Tar spot is a fungal disease caused by members of the Rhytisma family. The most widespread species of this fungus are the R. acerinum and the R. punctatum, both of which affect Chinese maple trees. Infected leaves develop green or yellow spots during the late spring and summer, which turn black during the summer. Sooty mold results from sucking insects and the sugary substance they secrete. The characteristic black coating is a fungal growth caused by several types of fungi. Neither tar spot nor sooty mold are toxic to plants, but if left untreated stunt foliage growth. Treatment for tar spot requires an application of a fungicide, while treatment for sooty mold requires getting rid of the pests that are present.

Canker

Canker is a fungal infection that affects the living tissue of the plants and is particularly prevalent in times of stress. If left untreated, the fungi can cause serious damage or death of the maple. Girdling of stems and twigs is an early symptom soon followed by foliage discoloration. Environmental stress, including recent transplant, insect infestation or disease increases the risk of canker. Excessive humidity or moisture presents an ideal growing condition for the fungi. Cleaning dead or fallen debris greatly reduces the infection risk.

Anthracnose

Anthracnose is a fungal infection that curls and discolors leaves before prematurely dropping. The fungus is at its worst after uncommonly cold weather, usually when excessive rain falls. Generally, one infection of the fungi doesn't pose a serious threat, but infections that return cause serious problems. These constant outbreaks weaken a tree's health, leaving it open for more serious problems. The fungi often enter the tree through wounds or pruning damage and must be treated with a targeted fungicide.

Maple Wilt

Maple wilt is caused by the soilborne verticillium fungi. This fungus does best in damp conditions and lives in soil indefinitely as long as it's undisturbed. Infected trees present symptoms that resemble normal fall defoliation. Dry weather brings out more obvious symptoms, including leaf discoloration that begins at the bottom and moves towards the top of the tree. During later stages of the infection, lesions appear on the leaves before they dry out and fall. Stunted growth and reduced foliage production are often side effects of long-term infection. Treatment includes ridding the area of dead or damaged plant parts and fungicide application either as a preventative measure or once the tree has been infected.

References

• Purdue University; Tar Spot on Maple; Peggy Sellers; 2005
• The Ohio State University; Sooty Molds on Trees and Shrubs; Stephen Nameth, et al.
• University of Minnesota Extension; Cankers on Trees; Connie Reeves, et. al; January 1999
• Iowa Department of Natural Resources; Anthracnose of Shade Trees; C.J. Luley, et al; July 2006
• University of Delaware; Maple Wilt; Bob Mulrooney; January 1999

Resources

• Gardening Central: Chinese Maple Tree
• Maple Tree Care: Chinese Maple Tree
• Tree Help: Maple Tree Insects and Disease
• The United States National Arboretum; USDA Plant Hardiness Zone Map; Henry M. Cathey; January 1990