Black spots on leaves - Ask Extension
My tree lost a leaf today that is covered in large black spots. The texture of the spot is different from that of the rest of the leaf and on the back...
Knowledgebase
Black spots on leaves #811428
Asked September 19, 2022, 4:19 PM EDT
My tree lost a leaf today that is covered in large black spots. The texture of the spot is different from that of the rest of the leaf and on the back the blackened areas are discolored, but only as a light brown. Looking into the tree, more leaves appear to have the same condition. I have a series of photos in a shared file: https://buckeyemailosu-my.sharepoint.com/:f:/g/personal/peltier_15_osu_edu/EkfixfvFDIxLj4yjIMbm-R0BDW7BFVdR7sBIBKckmOtgAg?e=5VU9zg in case the attachments don't have enough detail.
Franklin County Ohio
Expert Response
Shannon,
This appears to be tar spot, a foliar disease of maple caused by two species of fungus in the genus Rhytisma, as explained in detail in below link from Michigan State University Diagnostic Services. Judging from the size of the spots, your leaves have R. acerinum, which produces large spots between 0.5 and 1.5 inches. Otherwise, it would be R. punctatum, which produces pinpoint-sized lesions.
Since these appear to be mature trees, spraying would be costly and ineffective. Rake up and destroy leaves in the fall as opposed to mulching as specifically directed in the second link below from Wisconsin University. Destruction of infected leaves can potentially mitigate the disease.
It is unfortunate that this happens, especially as we look forward to the beauty of autumn leaves. I learned about it the hard way, about a year after I planted a new expensive maple tree.
https://www.canr.msu.edu/news/black_polka_dots_on_maple_tar_spot
https://hort.extension.wisc.edu/articles/tar-spot/
This appears to be tar spot, a foliar disease of maple caused by two species of fungus in the genus Rhytisma, as explained in detail in below link from Michigan State University Diagnostic Services. Judging from the size of the spots, your leaves have R. acerinum, which produces large spots between 0.5 and 1.5 inches. Otherwise, it would be R. punctatum, which produces pinpoint-sized lesions.
Since these appear to be mature trees, spraying would be costly and ineffective. Rake up and destroy leaves in the fall as opposed to mulching as specifically directed in the second link below from Wisconsin University. Destruction of infected leaves can potentially mitigate the disease.
It is unfortunate that this happens, especially as we look forward to the beauty of autumn leaves. I learned about it the hard way, about a year after I planted a new expensive maple tree.
https://www.canr.msu.edu/news/black_polka_dots_on_maple_tar_spot
https://hort.extension.wisc.edu/articles/tar-spot/
