Dark spot on cactus
Hi, I have had an Arizona Organpipe cactus for about a month and a half. I’ve watered it twice. It’s in a very bright room with a lot of windows but isn’t getting direct sun. I check it over regularly and yesterday discovered a dark spot. Can you help me identify it so I can prevent a catastrophe? Thank you!
Douglas County Colorado
My guess is that your organpipe cactus (Stenocereus thurberi) has a bacterial necrosis as indicated by the round darkened area on the limb. According to the University of Arizona Extension Office, in early stages you may be able to cut out the infected area and disinfect the cactus with a very weak bleach solution to prevent spreading. Additionally, over irrigation will cause plant failure. When growing indoors, these cacti should not be watered from November through February.