Please can anyone identify these black spots on my cactus

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Rich66
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Please can anyone identify these black spots on my cactus

Post by Rich66 »

Hi
Can anyone identify these black spots on my Micranthocereus Estevesii? They are hard to touch and have a shiny appearance to them. They begin as a dark blue to purple spot under the skin of the epidermis and then come to the surface and turn black and hard and have a shiny appearance to them. I’ve picked on off before and it scared the plant. Please can anyone help me.
Many Thanks
Rich
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RAYWOODBRIDGE
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Re: Please can anyone identify these black spots on my cactus

Post by RAYWOODBRIDGE »

Looks like sooty fungus.
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Re: Please can anyone identify these black spots on my cactus

Post by SimonT »

Looks like scale insect to me.
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Re: Please can anyone identify these black spots on my cactus

Post by Aiko »

I would not rule out frost damage. But then of course there should have been frost since this occured...
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Re: Please can anyone identify these black spots on my cactus

Post by Tina »

I'd agree with cold damage
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Re: Please can anyone identify these black spots on my cactus

Post by Aiko »

Aiko wrote: Thu Sep 23, 2021 10:07 am I would not rule out frost damage. But then of course there should have been frost since this occured...
I only now noticed it has a blueish epidermis. That for me is usually a sign it likes it warm. So I guess it could get scarred even when it is above freezing but just too cold for it anyway (colder than 10C or so). I am not really into Brazilian cacti, one reasing being their potential intolerance of cold and specifically frost (although I am sure there are a few that don't mind freezing).
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Re: Please can anyone identify these black spots on my cactus

Post by habanerocat »

I had a Tunilla like that after spraying it with a neem oil solution.
But if it hasn't been sprayed I'd put it down to the cold.
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Re: Please can anyone identify these black spots on my cactus

Post by SimonT »

It still look like scale to me.
You can get sooty mould with scale as they can produce honeydew which then starts the mould.
Scale also can blacken if you kill it- so it shows up better once pesticides have done their job!
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Re: Please can anyone identify these black spots on my cactus

Post by Rich66 »

Hi everyone
Many thanks for your feedback and advice. I do have a heated greenhouse, but if it does get to cold I do bring them indoors. I’ve got other micranthocereus’s and they are fine. So if it is some sort of mold or scale what treatment would you recommend? and what is the minimum temperature these cactus like?
Many thanks
Rich
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Re: Please can anyone identify these black spots on my cactus

Post by SimonT »

I think you'll hear lots of different preferences as to which pesticides to use but I found the general RHS guide quite useful. https://www.rhs.org.uk/advice/profile?PID=224 Personally I use Bug Clear Ultra if required.
If you do have scale then it can be quite persistent and you might have to do more than one treatment.
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