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Tar Spot on Maples (Black Circular Spots)

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A-Star Arborist

A-Star Arborist

Date Joined:
Jun 17, 2010

Posts:
166

Posted: Wed Mar 23, 2011 08:12 PM

Subject: Tar Spot on Maples (Black Circular Spots)

We often get called because customers think that their trees have a disease. Well they sort of do, but completely harmless and completely unavoidable. The spots appear light green in the spring and become dark black in the summer with a small yellowish ring around the black spot. This does affect minimal amount of photosynthesis.


This is commonly found on Norway Maples. The spots are a fungus that are held to the leaves. The leaves are the only infected part of the tree. Since the leaves do fall off in the fall their is no long term damage. The only way to correct the problem is to rake up all your leaves in the fall and have them removed from your property. It only takes 1 leaf to overwinter and the whole process takes another year to fix. Since this is an airborne transfered fungus it is necessary to have all your neighbours and park leaves infected removed. This is impossible and will never happen.


I have noticed that this happens more on shady trees when it is moist out for a few days. Pruning your trees may resist a little, by having more light in to dry the leaves.

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