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What Are These Spots On My Leaves

Post Date:10/24/2017 11:04 AM

tar fungus

What is tar spot fungus:  Tar spot is a common, visually distinctive and primarily cosmetic fungal leaf spot disease.  While tar spot can affect many species of maple, this disease most commonly affects silver maples. 

What does the disease look like:  Initial symptoms of tar spot are small (approximately 1∕8 inch) yellowish spots that form on infected leaves.  These spots may remain relatively small, or may enlarge over the growing season to roughly 3∕4 inch in diameter.  As tar spot progresses, the center of the infected area becomes raised and turns black.  This black area resembles a blob of tar on the leaf surface. 

What is the cause of tar spot:  Several fungi in the genus Rhytisma (most commonly Rhytisma acerinum and Rhytisma punctatum) cause tar spot.  These fungi commonly survive in leaf litter where they produce spores that lead to leaf infections. 

Should you be concerned about tar spot:  Don’t panic!  For most maples, tar spot is not a serious disease.  It is primarily a cosmetic disease that makes the tree look a little ragged, but does not kill the tree, nor even cause serious defoliation.  Fungicide treatments for tar spot are rarely, if ever, warranted.  You can reduce tar spot by simply removing fallen, infected leaves from around the base of your trees each fall.  Infected leaves can be disposed of, burned, buried or even composted. 


Heather Stevenson

Village Forester

Village of Oak Lawn

ISA Certified Arborist IL4613A