Anthracnose is a group of fungal infections that present roughly the same symptoms on several varieties of landscape trees. However, although these infections look similar, they are specific to the host they infect. For example, ash anthracnose will only affect ash trees and poses no threat to other varieties of tree. Oak, maple and walnut trees each have a different fungus specific to that variety that causes anthracnose.
Symptoms of Anthracnose
The fungus which causes anthracnose over-winters in infected leaves, twigs and branches. In the spring and summer during periods of cool, wet weather, spores from the fungus are spread by rain and wind. Buds, shoots and emerging leaves are then infected with anthracnose.
Anthracnose infections first present on new growth and leaves. New shoots may be brown and twisted and leaves will have brown-colored spots. As the infection gets worse, leaves will have black or necrotic spots and may curl or fall off. Although a tree may lose a significant amount of leaves from anthracnose infections, it will put out a second set of leaves after defoliation.
Anthracnose symptoms start in the lower and inner branches of a tree where humidity and moisture levels are higher. This differentiates anthracnose infections from root or wilt diseases which start in the canopy of the tree.
Controlling and Treating Anthracnose
Anthracnose does not generally kill host trees. However, severe infections can reduce the vitality and appearance of landscape trees. Trees stressed by drought or improper nutrition are more susceptible to infection. The best prevention of further infection is good cultural practice. Prune out dead or dying branches and rake and dispose of leaves in the fall. Maintain the vigor of the tree with proper moisture and fertilization.
Often, fungicide application is unnecessary because anthracnose is not a serious problem for healthy trees. In the case of very large trees, fungicide application can be difficult and costly. Fungicides are recommended in cases where young and stressed trees are showing decreased vigor from severe anthracnose infections. It is also recommended in cases where a tree has been defoliated several years in succession. Recommended fungicides include chlorothalonil or thiophosphate-methyl.
Although anthracnose is a common fungal infection, homeowners can prevent it from spreading or re-infecting landscape trees with simple sanitation practices and maintaining the health of the tree. Healthy trees may be unsightly for a while but anthracnose will not generally cause permanent damage.
Sources:
Ash, C. Anthracnose of Ash Trees. Yard & Garden Brief, University of Minnesota Extension. http://www.extension.umn.edu/yardandgarden/ygbriefs/p413ashanthrac.html
Anthracnose Diseases of Shade Trees. Greenshare Factsheets, University of Rhode Island Landscape Horticulture Program. http://www.uri.edu/ce/factsheets/sheets/anthractrees.html
Paula Lovgren - Paula is a freelance writer, gardener, garden designer and mother to two children and three cats. She has previously worked as a marketing ...
Join the Conversation