Knowledgebase

Marssonina Leaf Spot #924987

Asked February 24, 2026, 12:03 PM EST

What is the best way to treat this on older aspen trees in Berthoud?

Larimer County Colorado

Expert Response

Hi Jeannie,

We corresponded last week and I gave you some information. I had asked you what fungicide your tree care company wanted to use to do the basal drench. I don't believe I heard back from you?

If you are just interested in doing a foliar spray, typically done at budbreak, those include: chlorothalonil or daconil. In dry years, where the fungus is not as present, the fungicides may appear to work better than they normally would. If we have a wet spring, the fungicides may largely be ineffective, if they are not applied at the correct time. 

Please note that marssonina is not a disease that harms the overall health of your tree. Aspen are not long-lived in lower elevations. 
Alison O'Connor, PhD Replied February 24, 2026, 1:49 PM EST

Hi Alison,

 

I have not heard back from my arborist yet. What are your thoughts regarding bark banding for this fungus?

 

Jeannie

 

From: ask=<personal data hidden> On Behalf Of Ask Extension
Sent: Tuesday, February 24, 2026 11:50 AM
To: Jeannie Aiello
Subject: Re: Marssonina Leaf Spot (#0194903)

 

The Question Asker Replied February 25, 2026, 12:30 PM EST
Hi Jeannie,

I really would like to know fungicide your arborist wanted to use and then I was going to do research to see if it's effective. Typically, bark sprays are not used; fungicides are used on foliage. 
Alison O'Connor, PhD Replied February 25, 2026, 12:48 PM EST

What is bark banding for?

 

Jeannie

 

From: ask=<personal data hidden> On Behalf Of Ask Extension
Sent: Wednesday, February 25, 2026 10:49 AM
To: Jeannie Aiello
Subject: Re: Marssonina Leaf Spot (#0194903)

 

The Question Asker Replied February 25, 2026, 1:00 PM EST
Well, that's not what I'm entirely sure about - since it's not commonly used or done for fungal leaf issues.

I'm assuming that your arborist means bark banding = trunk spray?

It would be good to clarify this.
Alison O'Connor, PhD Replied February 25, 2026, 1:02 PM EST

I’m going to call them. So confused. They wanted to do bark banding vs. spraying due to the proximity of my neighbor’s home and yard.

 

Jeannie

 

From: ask=<personal data hidden> On Behalf Of Ask Extension
Sent: Wednesday, February 25, 2026 11:02 AM
To: Jeannie Aiello
Subject: Re: Marssonina Leaf Spot (#0194903)

 

The Question Asker Replied February 25, 2026, 1:10 PM EST
Please let me know what you find out!

And feel free to email me directly, instead of using this system: <personal data hidden>

Thanks :)
Alison O'Connor, PhD Replied February 25, 2026, 1:16 PM EST

Will do. They are in the field and will call me later.

 

Jeannie

 

From: ask=<personal data hidden> On Behalf Of Ask Extension
Sent: Wednesday, February 25, 2026 11:17 AM
To: Jeannie Aiello
Subject: Re: Marssonina Leaf Spot (#0194903)

 

The Question Asker Replied February 25, 2026, 1:30 PM EST

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