Can anyone shed any light on the disease affecting these plants? It usually starts as small blisters over varying amounts of the plant body. These turn black, sometimes they weep - and then scab over. It doesn’t kill the plants which look healthy otherwise and some cases are worse than others. The photos show the most obvious cases.
This started quite suddenly in a few plants in 2014 but the scars largely faded and I thought the problem had run its course and died out. But suddenly it is back with the original plants and probably others affected. I am not sure whether to abandon all the affected plants (not easy) or wait and see if it dies down again but with the possibility of it spreading further.
Has anyone else seen this problem?
Blisters resized.jpg (37.74 KiB) Viewed 3026 times
2014_Rebutia black scabs.jpg (116.63 KiB) Viewed 3026 times
I've never come across anything like this and I've no idea what could have caused it. It might be helpful if we knew a bit about your growing conditions. Are the plants kept in a greenhouse or indoors? What are the winter conditions, cold/heated? Have the plants been subjected to changed conditions or extreme conditions? The fact that this seems to have recurred among your collection is a bit worrying. Perhaps other forum members have some ideas.
Rod Smith
Growing a mixed collection of cacti & other succulents; mainly smaller species with a current emphasis on lithops & conophytum.
Sorry – I probably didn’t give enough details. I am Rachel form Sheffield and it worries me as well. I am new to the forum although not to cacti.
I have grown cacti for around forty years and never saw anything like this before. The plants are grown in an 8/6ft greenhouse and for the last few years have overwintered in an unheated attic room owing to so many being lost in the freeze of 2010/11. There have been no extreme conditions. They have been sprayed with insecticide on a few occasions owing to the occasional mealy bug appearing. They get a fair amount of attention. Most of the plants have been grown from seed or cuttings (by myself) or got through the society although I do occasionally ‘rescue’ plants that are in poor condition.
The problem first appeared in 2014 but didn’t seem to be obvious in 2015 – I thought the plants had recovered. Last winter I replaced my greenhouse. This spring every plant was repotted before being rehoused in the new greenhouse. All seemed well until a few weeks ago.
So far the plants affected have all been Rebutias or Sulco’s - although these account for the best part of what I grow so this may not be significant. I am keeping a close eye out for signs in other plants.
If any other details will help I will gladly provide them.
It looks to me fungal in nature, and I'd be using a horticultural fungal spray. Might be too little too late for that one with the black spots, but I'd be worried because fungal activity spreads by spores. During warm dry weather with good air circulation, it's not a huge threat, but in wintry damp conditions, can become a huge problem.
Also, I'm noticing old dead flowers on your plants. I usually remove them because I've seen in the past they can also foster fungal activity, as mentioned especially when there's dampness in the air.
Good luck, and I hope you successfully clear it up.
I have this happen on some of my Rebutia also some of my Trichocereus cacti too, it is odd and I have never found out what causes it, the black spots eventually go brown and scab over too, it doesn't kill the plants and hasn't spread to any of my other plants but it is a mystery why it happens.
This problem has been discussed several times in the past. If you search back through the forum threads using 'black rot' as the search term you will find several references to it as well as a few views on its cause.
Thanks. I am going to try fungicide and will also try and isolate the affected plants. However, I only see the problem in the summer -which doesn’t quite fit the fungal picture. I do remove flower heads later in summer when they have dried up. Today I put some tissue from the worst affected plant under a microscope and saw nothing convincingly fungal. (Not proof of course).
Interesting that this has been seen in other Rebutias, also without killing them.
Same as Lyn I have had minor outbreaks on Cerei, a Trichocereus pasacana. It did not kill the plant and it still occasionally breaks out. Not found anybody who has come up with a cure so far. Scroll down the link:-
"Bacterial necrosis of saguaro is caused by the bacterium Erwinia cacticida. The initial symptom is a small, light-coloured spot with a water-soaked margin on the surface of the trunk or branches that may easily go unnoticed. The tissue under the infection site soon becomes brown or almost black. As disease progresses, the tissue may crack and exude a dark brown liquid."
I have had damage like the first picture on rebutias which puzzled me for a while, but in my case seemed to be caused by field mice. They will readily eat rebutia gymno and epithelantha fruits. Presumably the urine is what causes the damage. It may seem a bizarre explanation but I have watched the damage develop on plants raided for their fruit so I am 99% certain that is the origin of the damage on my plants. Sure sign of mice in my greenhouse is the sudden disappearance of epithelantha fruits overnight!
