A sugar maple leaf showing markings from anthracnose, a fungus caused by abnormally heavy precipitation throughout the spring and summer of 2011. Effects of the disease, which also affected red oaks and ashes, was apparent as early as the end of spring. Browning continued throughout the growing season as infected leaves dried up.

Widespread anthracnose was a major factor in the generally poor 2011 foliage season. In addition to being a significant component of the northern hardwood forest in natural environments, sugar maples are frequently planted along roadsides, town commons, and backyards, and are arguably the region's signature foliage tree.