I’ve noticed those dark spots on the Red Maple in the summer, and they’re nearly invisible on the dark leaves – you only see them if you look closely. However, in the fall, they become much more visible, and I couldn’t resist finding out what they were. The contrast of black spots on yellow leaves doesn’t make for a very attractive maple tree.

By now, I’m sure everyone has heard about the infestations of the Asian Long-Horned Beetle, the Emerald Ash Borer, and the Yellow-Headed Spruce Sawfly. The latest concerns are the borer and the sawfly. The borer is an invasive insect that kills healthy ash trees of all species, while the sawfly exclusively feeds on spruce trees. It seems we’re missing a natural predator for these pests.

A classic scenario I experienced in my backyard was the infestation of ladybugs. This happened a few years ago, and every so often, I still find one or two of those pesky ladybugs in my house. Since their population declined over time, I’ve noticed more aphids in my garden. Releasing ladybugs, a natural predator of aphids, is one of the few effective methods to control garden aphid infestations.

Then there’s one experience I’ll never fully understand. About three or four years ago, while driving on Hwy 404 to work, just before Hwy 7, I noticed dark funnel-like formations atop many trees—not tornadoes, but something strange. It wasn’t just a few trees—it was hundreds. What kind of bug could it have been? I have no idea.

Maybe someone reading this post will have an answer.

So, what’s going on with the Red Maple trees on my street?

I was able to narrow it down to the tar spots. Known as black spot or tar spot, these markings on maple leaves are caused by fungi in the *Rhytisma* genus (though I’m not sure about the Latin—my skills there are a bit rusty). The infection typically occurs in late spring or late summer, and the affected leaves may fall off prematurely. Fortunately, these tar spots are usually not harmful to the maple trees.

In our case, it’s already November, and the leaves are falling due to the natural fall cycle. However, some are still clinging to the tree despite the spots.

And what’s the treatment?

The fungus overwinters on the leaves that have fallen to the ground. To prevent it from spreading, the leaves need to be raked up in the fall. If left on the ground, the spores will reappear in the spring on the old leaves and spread to nearby trees. While the fungus seems to have spread to all the trees here, everyone has been diligent about raking and composting the leaves. Hopefully, that will help reduce the problem.

As for treating your maple tree, it’s generally not effective. You can’t just treat one tree—you would need to treat all the trees in the neighborhood. For now, raking up the leaves seems to be the best solution.

COMMENTS

Marvin said: November 16, 2011 at 01:58

“Cutting down all the maple trees and planting oaks works too.”

Martin E said: November 16, 2011 at 20:01

“We have these tar spots on all our maples. as well. It is a relief to hear it isn’t bad for the trees! Is it only red maples? I think the on in our backyard is a Manitoba maple.”

Christopher Watts said: November 22, 2011 at 13:25

“Thanks Anna, I was wondering about these myself and this post is excellent in highlighting the cause and solution. Perhaps the town can help get the word out while it is educating everyone in the ash issue.

FYI Manitoba Maples are considered weeds. They grow quickly and choke out other plants and trees. Their root system is destructive if planted close to a house. They take some effort to kill too.

Red and Japanese Maples are much nicer trees in my opinion.”

Anna Lozyk Romeo said: December 20, 2011 at 23:43

“Chris, I did not know about the Manitoba Maples, and I did check them out for the future. We used to have a poplar tree; this thing grew out of the weed, and we had to remove it before it became too big. I agree, red and especially Japanese maples are much nicer.”