Identifying cause of lesions on cactus

[stevelatinner]

Hi,

I have a Peruvian Torch type cactus approx 10 years old, 4ft tall and 1 to 2 inches wide. It is planted in 100% compost and is rarely watered. I keep it indoors near a large window. It used to be in the window gathering more light, but now it's too tall to fit, so is close by on a table.

I have recently noticed the occurrence of lesions, both black and whitish grey. Including one big black lesion that weeped a black ink-like liquid, but now is dry. These are occuring on the darker side of the cactus (not the window facing side), and within 12 inches of the base. Any ideas on what they are and the cause?

Thank you

Steve

[hegar]

Those could be fungal lesions, but I think, that they are perhaps caused by some kind of mechanical injury a while ago. I would just keep an eye out on them, in order to see, if these lesions either enlarge or multiply. If there is indeed a fungus present, you will usually see either a mat of fine strands (mycelium) growing on the affected parts or there will be a formation of very tiny spherical or slit-like structures on these lesions. A fungus or other pathogen would also spread.
Another thing to look out for is a change in color around the spots. The plant tissue underneath could also become very soft and watery, which would indicate the presence of most likely a bacterial rot organism.
I do get to see columnar cacti collected in the wild regularly and most of the time the lesions are just blemishes, which - except for the cosmetic impact - do not impact on the health of the plant.

Harald