The Black Death?

[Ali Baba]

I’ve had this Melocactus azureus from a very small seedling and it has grown pretty well with occasional batterings from small children for a couple of decades. It has always been a house plant so never gets colder than 15C and watered all year around. This winter I had noticed some patches where the epidermis had become paler, these eventually form large black blisters, one of which has begun to ooze brown clear fluid. I’m guessing that the prognosis is not good, anyone else seen anything like this?

[ralphrmartin]

I once had something similar happen to a Borzicactus. I presume it's due to some microrganism - perhaps someone else can tell us which one? I'd chop the top off and try to rescue it as a cutting.

[esp]

I think I've seen it diagnosed as a bacterial infection. I had it on 3 Trichocereus seedlings. The 2 smallest died, it eventually healed over on the rather larger third plant, leaving a brown scar but seemingly no long term issues.
So if you don't fancy surgery, keep it warm and dryish and hope for the best.

[Ali Baba]

I once had something similar happen to a Borzicactus. I presume it's due to some microrganism - perhaps someone else can tell us which one? I'd chop the top off and try to rescue it as a cutting.

I’d imagine that chopping it without infecting the surface would be tricky if it is a bacterial infection, and I suspect rooting the top might also be a bit of a challenge

[Ali Baba]

I think I've seen it diagnosed as a bacterial infection. I had it on 3 Trichocereus seedlings. The 2 smallest died, it eventually healed over on the rather larger third plant, leaving a brown scar but seemingly no long term issues.
So if you don't fancy surgery, keep it warm and dryish and hope for the best.

That’s my plan, if it dies it dies

[RAYWOODBRIDGE]

Hi Ali
Many cacti have alkaloids just under the skin ( epidermis ) especially blue epidermis and quick growing cereus types ( Trichocereus/Pilosocereus ) when the body of the plant is bruised or even sprayed with chemicals it can cause it to go black, which then becomes a pustule and starts to leak out a brown resin type liquid.
If the plant is left alone warm and dry ( Melocactus ) it will heal up and leave a large brown scar which will slowly grow out.
The marks never disappear but a plant of that size should recover OK.

[Ali Baba]

Thanks Ray that’s interesting and reassuring. Curiously the side that faces the (kitchen) window is unaffected. Perhaps it objects to my kids cooking!

[habanerocat]

Is there any way to treat bacterial infections?

I've posted here before that I just can't grow Lobivia jajoiana. Seedlings just turn brown like a bad RSM infection.
Adult plants that I've bought turn black like in the picture above.

I'm seeing some black marks on some Gymnocalycium now also.

[SimonT]

I have one Aylostera that responded to a spray I use for mites by coming out in similar black/brown blotches.
Strangely I have another clone that seems quite happy being treated with the same spray.
My experience so far is that blotches seemed to either grow out or flake off over time.

I've seen a similar response to a plant outside that has had something dig a hole through the plant. So I guess the blackening might be a general
damage response. I think you just have to watch and see if the dark area continues to spread- if it does then the problem is ongoing and
you might have to do something drastic. Otherwise you could leave it and hope the plant recovers on its own. I've managed to spray my sensitive
plant again by mistake this year and so far 'waiting' seems to be working!

[Tina]

Its a nuisance, this was a denmosa rhodacantha I bought, over a foot tall and then this happened.
I did start surgery & then gave up- too messy & I had got the hump .
I'll find out next year if it makes it, it came unrooted which won't have helped.
It did get a spray with alcohol after this