White mold on maple trunk

Asked October 8, 2018, 8:18 PM EDT

We have a maple (looks like a crimson king maple based on the leaves and a brief search) with white arc on the trunk, shown in the attached photo.The white portions are 'fuzzy'. There are several arcs like the one shown on various places on the trunk, though none above about 6 ft. off the ground. What it the cause and does it require treatment? Thank you for your time.

Livingston County Michigan

4 Responses


Thank you for your question. I will have to do a little more research into this. It does look potentially fungal, based on the semi-circular pattern, the white fuzzy growth, and the sort of water-soaked looking region in the middle.

How did the leaves of the tree look, now and earlier in the season? Did the tree seem healthy, other than these areas? What kind of soil do you have, and what is the moisture-level in the soil like around the tree?

If you could send a few more photos for perspective, that would be helpful. A zoomed-out photo where more of the tree can be seen; a photo that includes the leaves; maybe a second example of one of the arches.

Thanks for your help.


Hello again,

I was informed by a colleague that this growth may be from a condition called "smooth patch" or from lichens. Neither of those conditions are harmful to tree health.

Please see the following Extension article from the University of Minnesota (linked below):

Non harmful tree conditions from UMN Extension

Please let me know if you have additional questions. Feel free to answer my questions from above or send additional photos.




I conferred with Dr. Jan Byrne from MSU Plant and Pest Diagnostic Services, and she basically said that it's hard to tell for sure what the "white stuff" is just from the photo. You might want to contact her about whether you should send a sample to the lab, and if so, HOW to take a proper sample.

Jan Byrne
Plant Pathologist
578 Wilson Rd., Rm. 114
(517) 355-3504

In the third photo (close-up of the leaves), it looks like the leaves have tar spot. Tar spot occurs frequently in Michigan, and is mostly an aesthetic issue, and not particularly harmful to overall plant health.

Please see the following articles:

Why do my maple leaves have spots?!

Black dots on maple: Tar spot