I've had a few questions in my email in the last few weeks from people who have noticed (now that the leaves that were once in the trees are all over their lawns!) that their maple or sycamore leaves had strange spots on them this year.
If your leaves had black spots that were roughly the size of a dime, the good news is that you have nothing to worry about. While definitely unsightly, this condition is called "tar spot" and is purely cosmetic. Tar spot is a fungus of the genus Rhytisma. It doesn't cause any permanent damage to your trees. A very heavily affected tree may suffer from early defoliation, but will likely be fine next spring.
You can apply fungicides to your trees if you notice tar spot, but this is generally more trouble than it's worth. If you'd like to try to avoid the issue next year, be sure to rake well. You can compost the leaves, but the compost pile should either be covered or turned well (so infected leaves are on the bottom) before the trees bud in the spring. This insures that when any spots mature (and produce spores), they can't simply re-infect nearby trees. Composting will destroy most of the tar spots before they're able to mature. It's worth noting that having an infected tree nearby may still cause problems for your trees.
I hope this has alleviated some of the concerns about spotty maple leaves. My trees had them this year as well as last year, and with a neighborhood full of mature maples, it's entirely possible we'll be seen more spots again next year.
Have you noticed tar spots on your maple leaves this year?