My friends and clients have been asking me about the black spots that they see on their maple trees. The spots are caused by a fungus called—aptly—tar spot.
It can appear on all types of maples (with the exception of Japanese maples), although this is the first year that I have seen it on my parkway silver maple. Lots of the Norway maples in my neighborhood seem to get this every year.
The good news is that while this is unsightly, it affects only the leaves and doesn’t usually hurt other parts of maple trees, but leaves with tar spot spores left on the ground will spread to other maples next spring.
Best way to deal with this? Good housekeeping. Keep the area around your maples clean as a whistle. That means rake up those ugly, spotted leaves, bag ‘em and put them in the dumpster. According to the Morton Arboretum website: “Composting may not completely destroy spores because most home compost piles seldom heat up enough to kill fungal spores.”