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Tomato leaf spots #936693

Asked June 24, 2026, 2:29 PM EDT

My patio potted tomato plants have developed dark blotches on the leaves. I'm trying to find the cause and what to do about it.

Crow Wing County Minnesota

Expert Response

It is likely a leaf spot fungus. See these web pages.
https://extension.umn.edu/plant-diseases/tomato-leaf-spot-diseases
https://www.canr.msu.edu/news/septoria_leaf_spot_on_tomatoes_preventing_spots_before_your_eyes
https://extension.umd.edu/resource/key-common-problems-tomatoes/
For a definitive diagnosis go to the Plant Disease Clinic
https://pdc.umn.edu/ There is a fee for this service.

Linda G Tenneson, Benton County Extension Master Gardener & Tree Care Advisor Replied June 24, 2026, 5:05 PM EDT

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This work is supported in part by New Technologies for Ag Extension grant no. 2020-41595-30123 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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