Tar spot of maple is a leaf disease that shows up every year. And like every other year, people worry that their maple trees are sick or dying. Luckily, tar spot is a disease that looks much worse than it actually is.
It is showing up early this year, likely due to the rainy spring we had in northeast Illinois. Right now it is in the early stage, where the spots are yellowish with black specks in them that may go unnoticed. As the disease develops, the spots will look just like shiny black spots of tar flung about on the upper surface of maple leaves. The spot most commonly infects leaves of silver and Norway maples, although red and sugar maples are also susceptible.
It does little harm to the trees, but is unsightly. While it is only July, maple trees have already received the majority of the functionality they will get all growing season from their leaves. Therefore, some lost leaves will not do much harm to the tree. Fungicide/chemical treatments generally are not necessary. To reduce inoculum, rake up and discard the leaves in fall.
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