Maple tree leaves are distinct in shape and well-known for their colour in the fall. When disease attacks the leaves, you may see the tree turn from beautiful to an eyesore. Knowing about conditions that can affect the leaves of maple trees may not help you prevent the disease or help you instantly return lustre to the leaves, but the knowledge may help you protect the tree.
Leaf Spot Diseases
There are many types of leaf spot diseases, but they are all caused by a fungus or bacteria (see Reference 1, "Leaf spots"). One variety that affects maples trees is Phyllosticta leaf spots, which, according to the University of Minnesota's Agricultural Extension, can be identified by "tan or brown spots with darker margins" (see Reference 3)/ Tar spots are another common variety of leaf disease and can be identified easily by black spots that look like drops of tar (see Reference 3). Leaf spot diseases do not usually cause damage to the tree itself, though this disease can make the tree look unhealthy. The best control is proper watering, pruning, and fertilisation.
Verticillium wilt is caused by a fungus that begins in the soil (Reference 1, click on more info: "Verticillium Wilt"). This disease will cause the maple leaves to turn a light colour and then drop. Verticillium wilt can affect the whole tree, or a part. In severe cases, the tree may lose entire limbs to the disease instead of just leaves. Controlling verticillium wilt is nearly impossible, although occasional pruning and fertilisation will help (Reference 1, same).
Powdery mildew is a relatively common leaf disease that appears as a white residue on the maple leaf (Reference 1, click on more info: "Powdery Mildew"). When the powdery mildew fungus prepares to winter over, mildew spores appear as black dots on fallen leaves. In order to control any outbreaks, spraying anti-fungal herbicides may be useful (Reference 1, same).
This genetic disease results from lack of nutrients in the leaves, causing them to turn yellow (see Reference 1). Some cases of chlorosis may result in the leaf veins remaining green while the leaf itself turns to the yellow shade. As this is not caused by bacteria or fungus, herbicides will not be useful. Applying nutrient compounds to the leaves may prove beneficial, as well as working to alter the pH of the soil (Reference 1).