Notice black spots on maple leaves?
The city of Janesville started its two-week leaf collection today. Did you get your leaves raked out to the curb line over the weekend?
If you did, perhaps you noticed black spots on some maple leaves. I was walking our dog a week ago on Saturday morning when I first noticed it on otherwise yellow maple leaves a block or two from our home.
Right away, the thought crossed my mind of an invasive insect I’d read about earlier this year, when the city announced the emerald ash borer had been found in Janesville. I arrived home to tell my wife about the spots, and Cheryl was listening to WCLO’s “Flower Hour” featuring Phyllis Williams of K&W Greenery. Phyllis was just finishing up explaining to a caller what those spots were all about, and I didn’t catch all the details. Cheryl pointed out that our maples had them, too.
Sure enough; our two maples out front have leaves with dark fall colors, so I hadn’t noticed the spots. But they indeed had these black spots, often larger than a quarter.
I called Phyllis on Friday to get an explanation. She said the spots come from anthracnose, a fungal disorder that occurs when weather conditions are just right.
She said the fungus doesn’t threaten the trees in any way; rather, the spots are cosmetic.
“Think of it as a big pimple on the leaves," she told me. "It’s not something you should worry about. Sometimes the things that look really bad aren’t so bad, but the things you don’t see—such as tiny emerald ash borers—will get you.”
If you prefer to compost your leaves rather than push them to the curb for the city pickup, there’s no harm in doing so with these black-spotted leaves, Phyllis said.
The only way to eliminate the fungus is with a fungicide, but you have to do it preemptively, so it’s a waste of time, money and energy, Phyllis suggested.
The insect I was thinking about, by the way, is the Asian longhorn beetle. It invaded Chicago and can kill maples. Phyllis, however, said the Windy City seems to have it under control for now.
Unfortunately, she said, if the Asian longhorn does arrive here, it’s bigger and uglier than the emerald ash borer and not only likes maples but virtually every tree.
As Cheryl and I nurture our newly planted hackberry tree, that was disappointing to hear.
Greg Peck can be reached at (608) 755-8278 or gpeck@gazettextra.com. Or follow him on Twitter or Facebook
Nov 8, 2012 at 8:17 p.m.
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The ALB has been successfully eradicated from Chicago several years ago. It is because they caught it in time, and this cicada sized bug moves from tree to tree in a very slow manner and short distance. On the other hand, with the Emerald Ash borer, I don't know what is worse, the borer or all the municipal Arborists making inaccurate decisions on saving our third most important native tree. City of Chicago is showing everybody the way, by successfully treating Ash trees every three years. Then when all the untreated ones die, EAB will have no more food, and it's population crashes for good. Now with double doses of Imidacloprid saving trees for $10-$25 a year, expensive Arborists are not needed, as owner can just "pour it" around base of tree by mid May. Remember Green Ash lives over 300 yrs, and the White for 600. Our other parkway tree problem is incurable Verticillium Wilt affecting all of the Sugar,Red & Norway Maple. Same spot cannot be replanted with Maple for 10 years unless tarp covers ground for two years and kills the spores. Luckily the Wilt does not get spread from bugs like Elms DED. A good trees damaged root must grow into spot of ground where they are waiting.
Nov 6, 2012 at 12:50 p.m.
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Whew! Thank you! I will sleep much better tonight.
Nov 6, 2012 at 12:13 p.m.
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Dear readers: I received an email from Wayne White, board certified master arborist with Emerald Tree Care LLC, who says it's not anthracnose fungus but instead a very common leaf fungus disease called "tar spot on maple." He says it's only a cosmetic problem and provided this link, http://www.ppdl.purdue.edu/ppdl/expert/t..., which does seem to look like the spots I'm seeing in maples on Janesville's east side.
Emerald Tree Care LLC serves Wisconsin and several other Midwestern states.
Greg Peck
Nov 5, 2012 at 9:33 p.m.
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Yep, they were there 25+ years ago too... I remember trying to find a perfect maple leaf for school.
Nov 5, 2012 at 3:30 p.m.
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“Think of it as a big pimple on the leaves,"... "It’s not something you should worry about."
Try convincing a 16 year old tree that.
I'm just sayin'...
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