Chinese elm, black spots on leaves

Hello,

I acquired this elm from a greenhouse late last summer. It had about ten leaves when I got it. It responded well. I wintered it in non-heated greenhouse. We had a really mild winter so I treated everything with mancozeb in early spring.

Unfortunately, these black spots are taking over but I don’t think it’s Anthracnose.

Any ideas? Do I need to prune all infected leaves?

Thank you.

Can you rub the black spots off? If so, can you get a look at them with a magnifying glass. Actually looks like a type of scale, but hard to say from the pic without a closer look. If that’s the case I’d say remove infected leaves then treat.

No, I can’t scrape it off. It’s like tar on the leaves. Here is a closer picture.

Ewww! Sorry, but I’m no help with that. Should probably still remove the leaves that are affected to try to at least slow the spread. Hopefully someone who has seen that before will chime in. The closeup pic will probably help. Good luck.

Thanks for the advice. I pruned all infected leaves. We’ll see what happens.

Update. I defoliated the tree, treated it with Malathion (since I had already treated with Mancozeb in the Spring), and put it my recovery area in dappled light under the maples. The poor tree had about 5 leaves left. But…

Thanks for your advice.

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Yea! Love a happy ending!

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Lookin good! How does the tree look now, almost a year later? Did you ever figure out what the black spots were?
Bryan

Thanks for checking in. I never found out what the black spots were but so far they have not returned. Made sure to have good percolation by cleaning off the top soil that had developed over the fall and winter. Watching water and oxygen. I am adding beneficial nematodes to the water cycle as well.

If they return I’ll let you know. Fingers crossed.

That is a fungus called black spot. It will infect your elm tree every year about this time, after the first flush of new leaves. I have a 50+ year old U. Parvifolia that has the disease. The problem with the fungus is that is that it doesn’t kill your tree quickly, but weakens it over time. It is caused when you mist the leaves or keep the tree in an overly humid environment. The solution is to:

  1. Defoliate the tree completely while it is dormant.
  2. Bare root the tree and replant it in new soil. (The fungus is in the soil as well as in the leaves.
  3. Treat the tree with a systemic fungicide (check to make sure you are using a fungicide that works with elm trees.)
  4. Treat the trunk and branches with Neem oil. Repeat as new flushes of leaves emerge and every 4 weeks thereafter.
  5. DO NOT mist or allow rain or other water to drench the leaves.
    This is the process I have used and found to be effective. Here is a picture of my 50+ year old elm taken in late April 2021. It almost succumbed in 2020, but is doing very well now.

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Thanks for the info. I will take caution not to allow the leaves to get wet.