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Spring leaf drop and anthracnose

M. Grabowski, UMN Extension Educator

Fallen ash leaves infected with anthracnose.
M. Grabowski, UMN Extension 
Lawns scattered with fallen tree leaves in spring and early summer often point to infection of shade trees by anthracnose. Many common shade trees can be infected with anthracnose including ash, oak, and maple. Anthracnose is caused by several different fungi. Each fungus infects a particular type of tree. The fungal pathogens that cause anthracnose infect young developing leaves during cool wet weather. Symptoms include dark brown to black water soaked spots on leaves, curled or cupped leaves, and leaf drop in spring and early summer.

There is no management needed for trees suffering from anthracnose. Although the disease can be somewhat unsightly, it is only a minor stress on the tree. As the weather becomes warm and dry, tree leaves are able to mature without infection. Once leaves are mature they are largely resistant to the anthracnose fungi. Even trees that have dropped many leaves due to infection will produce a new flush of leaves and recover with warm summer weather.
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