Upon our return from vacation, our cactus had black splotches. In about 5 days it turned completely black. Sadly, I guess my question now are, is this contagious? How can it be prevented? And, how does one dispose of a giant sick cactus?
It can spread to other plants, but the risk is low as long as the disease is confined to the plant's interior. It is possible that the plant will collapse soon, which can facilitate spreading. It is not likely to spread epidemically, as for most cactus growers this happens to me as well and spreading from one plant to its neighbour is a very rare event. It is difficult to completely prevent it, these bacteria (my primary suspect in this case) and fungi are always present in soil and/or air. Overwatering is a common way to actually get a cactus infected by them, and good drainage is a way to minimize the risk. I am not familiar with what options for disposal that are available to you, but burning, burying or dumping in some nearby forest are some possibilites. Actually, this is one reason why I got rid of all my large cacti while they still were healthy ...
Thank you for the reply. I just found out it the city will pick it up with the recycling. Is there a name for this disease? The cactus was given to us because it wasn't getting much light where it was, but maybe the move was too much for it. Sad to put it out in the garbage, but we certainly don't want our other cactus to get it.
Cactus collectors just call it "rot", preceded by the type of organism that caused it, if known. It is very difficult to guess why it was infected, I cannot even see where it started. Overwatering, cold damage, physical damage during the move are possibilities. Sometimes it just happens anyway.
