Lots of spots on maple tree

In many cases, diagnosing plant problems requires an in-person look at the plant in question. Too many disorders look similar when all you have is a photo to go by.

Earlier this week someone sent me a photo asking about spots on a valuable tree they have in their front lawn. That was an easy one. I took one quick look at the photo and knew right away what it was. Their maple tree was infected with a fungal disease called “tar spot”. It’s quite easy to identify because in this case the name is very descriptive, the leaves really do look like they’re covered with spots of tar.

Even though it looks pretty bad, tar spot is relatively harmless even in a heavily infected ┬ásituation. There’s no good way of preventing the disease. Some years are worse than others for tar spot and some varieties seem to be disposed to having more dramatic symptoms than others.

Here’s the photo that was sent to me. Seeing tar spot for the first time can be quite startling.

The spores from the disease over winters in fallen leaves so you wound think that raking them up and disposing of them would help the situation. Unfortunately the fungal spores can travel for miles in the air and can land on your tree and take hold.

When a tree has a severe case of tar spot, it can lose many of its leaves causing your tree raking season to begin earlier than normal.

One bright spot is since tar spot is species specific, it will not spread to other types of trees such as oaks.

Bob Dluzen
As a result of being a gardener for more than 40 years, 30 of those as a professional, Bob's gardening has become an integral part of his life. "It's the ever-changing seasons and the wide variety of plants and gardens that keeps me intrigued," he says. Bob lives and gardens in rural Monroe County.