Hello Veronika,

Thanks for reaching out!

Good news! This a fairly common issue, but it doesn't cause any harm to the tree.

Here's the response from Ann Hazelrigg, our state plant pathologist:

This is a common late season fungal disease called tar spot. It does not really harm the tree because it occurs late in the season. https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/tar-spot-of-maple-rhytisma-spp/

Control is really not warranted but raking and destroying leaves may decrease the number of spores that overwinter. That being said, if your neighbors are not doing this, spores will be carried by wind to your susceptible trees. You could also mow over the leaves repeatedly to get them to break down quicker. I would probably do this rather than raking and mulching the leaves. You could do this a few weeks in a row as the leaves are falling so you don't have a huge amount at the end of the season. IF we have another wet summer, you will likely see it again but it does not affect the long term health of the tree.

Hope this helps! Happy gardening!

Hello Veronika,

Thanks for reaching out!

Good news! This a fairly common issue, but it doesn't cause any harm to the tree.

Here's the response from Ann Hazelrigg, our state plant pathologist:

This is a common late season fungal disease called tar spot. It does not really harm the tree because it occurs late in the season. https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/tar-spot-of-maple-rhytisma-spp/

Control is really not warranted but raking and destroying leaves may decrease the number of spores that overwinter. That being said, if your neighbors are not doing this, spores will be carried by wind to your susceptible trees. You could also mow over the leaves repeatedly to get them to break down quicker. I would probably do this rather than raking and mulching the leaves. You could do this a few weeks in a row as the leaves are falling so you don't have a huge amount at the end of the season. IF we have another wet summer, you will likely see it again but it does not affect the long term health of the tree.

Hope this helps! Happy gardening!