From what is seen in the pictures, anthracnose, a common fungus disease in maple trees, appears to have infected your tree. The anthracnose fungus overwinters in leaves that have fallen from trees and infected twigs and buds. This year, with the cool, wet weather, has encouraged fungal growth. It can spread by wind and splashing rainwater. Infected trees have leaves with dark, irregularly shaped lesions with dead areas between the veins and on leaf margins. While this disease is usually not a threat to the health of a tree, if the disease becomes severe enough, the leaves will drop from the tree.

To help control anthracnose rake up and destroy all fallen leaves. The fungus will remain on those leaves throughout the winter and cause anthracnose to appear the following spring. Be sure to leave as much room between trees to allow for airflow which creates an environment that does not allow the fungus to thrive.

Maintaining the health of the tree can help to reduce stress of the disease and reduce the spread of the disease and the possibility of a secondary invasion of insects. Make sure your tree is watered and fertilized properly.

If you would like to use a chemical to help control anthracnose on your maple tree, Bonide Fung-onil Multi-purpose Fungicide is the one chemical that can be used in Oregon for home use. More information can be found at: Maple (Acer spp.) - Anthracnose.