Falling Leaves in August?

By Mark Phoenix posted September 23, 2021

I noticed the Norway Maple trees around my house began dropping leaves in August this year.  The leaves that had fallen to the ground were somewhat brown and dry with black spots on them.  I thought that was odd and began to research this phenomenon.

I discovered that the Norway Maple trees have been infected with Tar Spot Disease.  In fact, Silver Maple, Red Maple, and other Maple trees are equally susceptible to this disease.

The cause for Tar Spot Disease in Maple trees is several different fungi.  The fungi cause pale yellow spots to appear on the leaves of Maple trees in June which then turn black over the summer, thus the name “Tar Spot” disease. 

The articles I’ve read on the topic seem to indicate that leaves left on the ground over winter can exacerbate the problem into the growing cycle the following year.  In the spring, the fungal tissue on the leaves that had fallen to the ground the previous fall will ripen.  Needle like spores are produced and are circulated in the wind infecting the new leaves which bloomed into the spring, starting a new disease cycle. 

According to my research, Tar Spot Disease does not cause long term damage to the maple tree itself as the fungi attaches to the foliage of the maple tree, only.

You might wonder how to rid maple trees of this disease?  It seems controlling the disease is difficult.  Raking the leaves, bagging, or otherwise destroying the leaves is one solution.  Mulching leaves will sufficiently destroy many of the tar spots before the fungi matures the following spring.  Spraying the leaves on maple tree leaves with a fungicide is another solution.  However, that may prove impractical and expensive, especially for those who have mature maple trees. 

According to what I’ve read, Tar Spot disease has become pervasive in New York State.  As I mentioned in the previous paragraph, controlling the disease is difficult.  Perhaps the easiest solution is to mulch or rake, bag, and properly dispose of the leaves this fall and hope for a better growing season next year!