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Weird yellow spots

Discussion in 'Issues, Disease and Pests' started by Mat Brutger, Dec 11, 2021.

  1. Mat Brutger

    Mat Brutger Active Member

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    Does anyone know what sort of disease/pest these yellow spots are? I’ve never seen anything like it in my collection.
     

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  2. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I don't know what that is. Does it scrape off? Have you tried putting some alcohol on it to see if that does anything.
     
  3. Mat Brutger

    Mat Brutger Active Member

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    It wipes off but not very easily. I treated it with Prontech but that didn’t do anything. I’ll try just alcohol. It’s luckily contained to just that plant and not even the new growth above it on the mount
     
  4. Raven

    Raven Well-Known Member

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    Does it look like a yellow powder bursting through the leaves? Similar symptoms on other plants are caused by rust fungi. Rust infections are pretty rare in orchids.
    There are a variety of systemic fungicides that can treat rust infections.
    Good thing is that most rust fungi species are very host-specific and capable to parasitize on closely-related plants only. Is it Ornitocephalus infected? If so, it could potentially spread to other Ornitocephalus species but won't affect distantly related orchid genera.
     
  5. Raven

    Raven Well-Known Member

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    Mat, I sent you a PM.
     
  6. KellyW

    KellyW Orchid wonk Staff Member Supporting Member

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    With a magnifying glass do the yellow spots (individual bumps) look identical? Just wondering if they are insect eggs.
     
  7. Chuck-NH

    Chuck-NH Well-Known Member

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    Agreeing with Raven, it really looks like classic rust to me, the only thing is I’ve never seen this on Orchids. It almost looks like Myrtle Rust or even one I’ve seen on Oxalis. In outdoor plantings of non-Orchids, we have been successful with an off the shelf fungicide like Daconil. I would recommend a dip rather than spraying if only one plant and brush off all the spores with a toothbrush while wet. Usually rust occurs when plants are a little too moist, particularly at night. Watching that and increasing airflow can help prevent further infection.
     
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  8. Mat Brutger

    Mat Brutger Active Member

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    Thanks everyone!