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Extension > Yard and Garden News > Maple tar spot strikes again

Friday, September 29, 2017

Maple tar spot strikes again

M. Grabowski, UMN Extension Educator
Tar spot may look different on different
species of maple. M. Grabowski, UMN

For the second summer in a row, tar spot, a fungal leaf spot disease is showing up in large numbers. Tar spot causes large black raised spots on leaves. Black spots are often shinny and look like wet tar. Although the symptoms of tar spot are most dramatic in the fall, the fungus actually infects the leaves early in spring when wet weather coincides with spore release. The fungus can only infect leaves, and will survive Minnesota’s winter in fallen leaves within leaf spots.


M. Grabowski, UMN Extension
Tar spot is not a serious threat to the health of the tree. The leaf spots may cause leaves to drop a bit early but not early enough to do significant harm. Gardeners interested in reducing problems with tar spot in the following year should rake up leaves and place them in a back yard or municipal compost pile.

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