The United States is home to a large and diverse group of maple trees, from the petite ornamental Japanese maple to the towering sugar maple. One thing they do have in common, aside from their colorful fall foliage, is a susceptibility to certain diseases. Some of the diseases are merely aesthetic. Others may stunt the growth of the maple tree or cause sections of the tree to die back. One disease--Verticillium Wilt--is deadly.
Anthracnose (Discula spp., Kabatiella apocrypta)
Anthracnose can be caused by any number of related fungi. This disease affects many different types of shade trees with varying degrees of severity. Maple trees are some of the worst affected by anthracnose, which attacks the trees during warm, wet springs.
The first sign of the disease is the appearance of spots on the leaves. The spots can be brown, tan or black in color and are usually asymmetrical. If the leaves are still developing, they can become distorted. While the disease can be highly unattractive, it is not life-threatening. Dropped leaves should be raked up and destroyed by burning or recycling (not in compost), as the fungi can overwinter on the ground.
Antracnose can be prevented with a fungicide application before the buds begin to open. Choose a fungicide made specifically to treat anthracnose.
Although this disease can attack trees other than maples, it is commonly found in maple trees and affects them very seriously. For this reason, Verticillium wilt is often called Maple wilt. This fungal disease (caused by the Verticillium fungus) can lie dormant in the soil for years, but can rise up and kill a maple tree (especially Norwegian maples) in just two or three growing seasons. Young trees and saplings can die in one growing season.
The disease causes the maple tree to become stunted. Leaves often become discolored, wilt or even drop off prematurely. The tree may die in sections, or all at once. There is no chemical way to treat this disease, and the only way to prevent it is to plant maple trees in areas where the soil is not infected by the fungus.
Canker disease is caused by the fungus Eutypella parasitica. The main symptom is the development of large cankers on the trunk or on the main branches of the maple tree. The cankers appear differently depending on the type of maple tree, but in general they appear as raised, elongated ridges of discolored, cracked wood.
In some maple trees, including the Norwegian maple, the cankers can girdle (encircle) a branch or even the trunk, cutting off the flow of nutrients to the branch or tree and killing it. In other maple trees, the cankers split or the bark peels off, exposing the tender inner part of the tree to other fungi that can rot the tree from the inside out.
The only treatment is to prune off or remove cankers, but this can leave open wounds on the tree, so pruning tools should be sterilized before use.