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My begonias aren't doing so well. They've developed spots on the leaves and it seems to be getting worse. I think it's some kind of disease, but I can't find a close enough match online to be sure.

begonias

If this is a disease, is it likely to spread to my other (non-begonia) plants?

Follow-up with additional information -

  • Location is east Tennessee. Weather has been fairly hot (85-95°F) with occasional rain.
  • The plant is on a patio, with a large wooden deck overhead. The location is fairly shady, but gets a couple hours of strong evening sun.
  • The undersides of the leaves appear normal (aside from the spots, which are visible on both sides of the leaves).
  • These are my only begonias, but there are other plants (oxalis, geranium, vinca, coleus) nearby. None of the other plants are exhibiting these symptoms.
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  • Is there anything unusual to be seen under the leaves, especially the affected ones? What's directly above your plant? A roof overhang, or guttering or something?
    – Bamboo
    Aug 25, 2021 at 14:20
  • @Bamboo I have updated the question with more information.
    – user42702
    Aug 25, 2021 at 20:31

2 Answers 2

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It looks like a type of bacterial leaf spot. Avoid getting water on the foliage. Chop off effected leaves and dispose in garbage bin (obviously avoid contact with other plants). Leaf spot typically spreads with excess moisture.

It could also be sunburn or frost burn. Frost burn is unlikely, as you would probably expect damage to start from the outside of the leaf. Sunburn could also be an issue, but that would depend on positioning (you should be able to answer that part).

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  • Thanks for your input. Bacterial leaf spot sounds likely - the darker spots look similar to pictures I've found online, but the lighter ones don't match anything I've been able to find. I considered sunburn and moved it into a shadier spot to see if it stops progressing. It feels unlikely though, the space doesn't get great sun except in the evening. And frost burn would be quite a feat, given the summer weather. :)
    – user42702
    Aug 25, 2021 at 20:36
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The plant itself is obviously pretty healthy in the main, evidenced by the new growth. The part that doesn't look too good is on the lower right hand side of the photograph, which has shrivelled brown areas.

At this stage, other markings look very like something has been spilt,, splashed, dripped or dropped onto the leaves rather than it being leaf spot; bacterial leaf spot usually has a yellow halo round the damage. What would be interesting is to see how the brown markings on the right hand side progress - will they look very like the markings on the rest of the plant over time, as well as whether the widely spread markings develop into holes.

I suggest you monitor it for a week or so because there's no obvious insect or fungal problem going on currently and the plant is otherwise healthy - if the leaf with the brown markings on the right hand side gets worse, but doesn't look anything like the rest of the marks, I'd remove that part, especially if it starts to yellow.

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