Over the past few weeks, I have fielded several calls from clients and concerned homeowners about the condition of their maple trees. Some are worried that their trees are dying, or that they will at least lose all of their leaves way too early. They explain that the leaves have large black spots all over and that many leaves have dropped suddenly over the past few days.
While I can understand the initial concern over the sick-looking appearance of their tree, luckily the tree generally looks a lot sicker than it actually is. What is typically affecting the tree is a leaf fungus called tar spot. Tarspot, of the genus Rhytisma, is a very common disease of maples that is currently widespread throughout the Chicago area. The disease manifests itself as dark spots on leaves that resemble tar. While the disease can be aesthetically unpleasant, infections are rarely a serious threat to the health of the tree. Heavy infections can cause early leaf drop, but even in this case defoliation typically occurs too late in the growing season to be a serious concern.
Treatment of leaf spot is not recommended. While there are fungal applications available, they are not considered worthwhile as their effectiveness is very limited. This, combined with the fact that the disease is not considered a major health concern mean that treatments are not recommended. The best thing to do is to keep the tree healthy in other aspects. The disease is also very weather-dependent, so infections are heavier in some years than others.
So if your maple has leaves looking like the one in the picture above, don't be too concerned. Just keep the tree happy and hope that next year isn't such a heavy year for the disease.