Japanese maple leaves have brown spots - Ask Extension
My potted young Japanese maple has brown spots, which I first noticed on 5/24. I just purchased it last spring, and repotted in late summer, and it's ...
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Japanese maple leaves have brown spots #870680
Asked May 29, 2024, 10:54 PM EDT
My potted young Japanese maple has brown spots, which I first noticed on 5/24. I just purchased it last spring, and repotted in late summer, and it's looked healthy so far this spring. What is the issue, and how might I remedy? I potted it with a potting and bark mulch mix, and as it's outside, I rarely water it, but have a few times this month. It's in full sun, the large yellow tree in the green pot. Thank you for any insights and recommendations.
Washington County Oregon
Expert Response
Thank you for your question, Julie. I believe your tree has one of the fungal infections described here: https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-leaf-spots
Unfortunately, once the fungus has gotten a foothold (so to speak) in the leaves, there is no "cure" for it. You need to take preventative actions. As the article says, at least rake and destroy fallen leaves, so the fungus does not remain viable in them. You can remove the infected leaves if you want, but that isn't an ongoing control. None of the chemicals listed appear to be available to homeowners, but the Bordeaux is organic, and you may be able to obtain it to apply next spring when the leaves again bud. You might also use the information in this article to make it yourself: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7481.html
Too late this year; better luck next!
Unfortunately, once the fungus has gotten a foothold (so to speak) in the leaves, there is no "cure" for it. You need to take preventative actions. As the article says, at least rake and destroy fallen leaves, so the fungus does not remain viable in them. You can remove the infected leaves if you want, but that isn't an ongoing control. None of the chemicals listed appear to be available to homeowners, but the Bordeaux is organic, and you may be able to obtain it to apply next spring when the leaves again bud. You might also use the information in this article to make it yourself: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7481.html
Too late this year; better luck next!
