fungus on Gymnocalyciums!

[Paul Siebold]

17.4.20, 11.16, Paul Siebold many thanks…

Hello all Cactophiles in glorious isolation! I hope you’re all enjoying your cacti despite no contact with the outside world!

I have a collection of about 140 cacti in my Halls 6 x 10ft greenhouse, Mammillaria, Rebutia, and lots of others all growing perfectly! There’s plenty ventilation in two roof vents and one auto vent other side, also a louvre window up one end, I have a Bio heater/fan which can blow cold air at base! Most of my cacti are happy with no mould or symptoms of bad ventilation! I have about 12 Gymno’s and they’re a different matter! I know they prefer shade which they get, and know they’re lack of spines make them vulnerable! All the more spiny cacti are happy and don’t show signs of fungus! But Gymno’s are a different matter! Some of mine have developed brown spots, I thought it was burning, but now realise its mould, bad ventilation! The smaller ones seem to get it! Like Gymno damsii, neuhuberi, marquesii etc, the bigger plants seem ok! I think I need a small fan at bench level, can anyone give me suggestions and a source? The mentioned Gymno’s I’ve isolated outside thinking the fungus might catch! Your help please!

[Diane]

Can you upload a photo of the affected plants? You are assuming it's a fungal problem, but that might not be the case. A photo would help determine what the problem is.

Take your photo, click on the attachments button below the posting box, and you will be asked to choose the file from your device.

Good luck!

[Mark07]

Yes as Diane has said, a photo would be great so we can check

I’m also intrigued because I’m currently experiencing a similar problem with black/brown spots spreading quickly through some plants. I’m convinced mine is also some kind of fungal disease.

[Paul Siebold]

[Paul Siebold]

Thank you Diane and Mark! This is my first picture posted on Forum EVER!! Took me awhile to fathom it but I succeeded! I'd isolated(another use of this word at moment!)the four Gymno's but they're back on greenhouse floor, but i have watered them with a fungicide! This one is a gorgeous Gymno baldianum a lovely red, which is all the more galling! I always thought it was sun scorch as Gymno's are prone to!

[Paul Siebold]

[Paul Siebold]

This is Gymno damsii with fungus/mould, and I've had many plants go and replace with another! Just again thought damsii was liable to burning but not the case! All my larger Gymno's are perfectly ok, maybe i should water them with fungicide in season! I look forward to your help!

[Diane]

Paul, I have to admit that I've no idea what the problem is with your Gymnocalyciums, because I've never had this problem. If it is a fungal disease, the only suggestion I can give is to try a fungicide such as Rose Clear, but this might not have any effect on the problem. It would help if you can describe the conditions you are growing them in e.g. minimum temperatures, and potting medium. Sometimes cold and damp will have an adverse effect on cacti.

Mark, there is a fungal disease that sometimes affects opuntias, causing these black spots - again, maybe damp and cold. If you have an unaffected offset, it might be a good idea to root one, and hope the problem doesn't appear again. I don't think there is much you can do to cure it.

Hopefully someone with more experience than me can comment, and come up with more ideas.

[Mark07]

Paul, yours does look like scorch damage so I can see why you thought this initially but like Diane says I’ve no idea otherwise, sorry.

Diane, thanks for your advise. I’ve also read up on that particular fungal disease that effects Opuntia and I also thought that this could be the same thing. I’ve removed the effected offsets from one plant but this unfortunately only left main stem which doesn’t look in the best of shape so only time will tell if I can save it. I’m keeping a close eye on the Opuntia invicta as it seems to have healed itself from the last attack but if it looks to be spreading I’ll have to separate offsets from this as well which will be a shame as its one of my favourites!

[Paul Siebold]

Diane, I think damp and cold does really have an effect on my smaller Gymno's, the bigger older ones seem to come through damp cold winters ok, and all my spiny ones ok, maybe keep them in propagator over winter! I grow a lot of genera and only ones have trouble with is these smaller Gymno's! And no cursed mealy bugs either!

To Diane and Mark, thanks for your help!