As cool wet weather persists in Minnesota this year, a common leaf blight disease of shade trees known as anthracnose thrives and spreads. Anthracnose is a fungal disease that causes leaf blotches, leaf distortion, shoot blight, and leaf drop. This disease is caused by several related fungi that thrive in cool wet conditions. Ash, maple and oak trees are all commonly infected with anthracnose and symptoms of the disease have been seen on all of these trees this spring. Despite blackening of leaves and shoots, anthracnose actually only results in a minor stress on the health of the tree. Only young growing leaves and shoots are susceptible to infection. Mature leaves are relatively resistant to the disease. Once warm dry weather arrives in Minnesota, leaves will mature and trees will replace lost leaves with a new flush of growth. As long as cool wet weather persists, however, expect this fungal disease to spread throughout the trees canopy. More information can be found about this disease at the UMN Extension publication on anthracnose in shade trees.