I fell in love with cacti after visiting the Desert Botanical Garden in Phoenix, AZ. I bought my first big cactus last summer. When I went to bring it in before the frost, I noticed it was flowering! I also noticed it had several places where it appeared damaged. I'm in Zone 6b. It's in my garage under timed lights. I'm attaching pictures of the damage. Any advice on how to repair it would be great. Thank you so much!

Hope someone can help.
Might possibly be a
Candelabra Plant (Euphorbia lactea)

or

Euphorbia trigona?
https://interiorfoliage.com/co...

@sallyg Thank you. The cactus is a Candelabra Cactus, a species of Spurges (Euphorbia) per Plant Identifier.

The question was specific to what may be causing the black spots. Rot? Bugs? Fungus? I want to save it.

@kaktus I hear you are the cactus doctor. Any thoughts here?

So technically, not a cactus, it's a cactus-like succulent. They belong to the spurge family.

Euphorbia vs Cactus
https://www.house-plant-hobbyi...

@calif_sue Thank you. I'm a plant lover. I just want to know how to save it. Do you know what the black stuff is? That's what I'm asking about.

Do you live in Arizona? Are the yellow areas surrounding the black spots on just the top surfaces of the stems? It looks like it may have gotten sun scalded. If that's the case, the black spots will either dry up or rot and I don't think there's any intervention at this point.

@lucy68 I am in Kentucky. It's been kept under artificial light in my garage since it came in pre-frost. My concern originally was aphids it may have picked up from being outside. I don't want to spray it with anything until I know. I've sprinkled food grade diatomaceous earth on the top of the soil. There are sticky traps around it also. I just don't know what it is.

Are the yellow areas on the tops of the stems only? What Lux/lumens are your artificial lights? How far from the plant? What kind of light did it have outside. Its not a disease or insect infestations, its mechanical damage.

Can you back up and take a photo of the entire setup with plant?

@Lucy68 Thank you. I appreciate your help. The lights are timed for 8-12 hours and they are adjusted daily. Here are a couple more pictures. It may be too cold for it in my garage. It is soft on that one spot. Wilting. That one branch has it on all 3 sides.

Welcome to the forum @DuchessDukelow
Don't know who give you the idea that I am good in keeping C&S, I like to chop those plants, but that don't make me an expert in keeping them.

The brown part in the last photo looks like stem rot, you may need to cut the brownish/soft part by 1 to 2 inch until you see the fresh and healthy plant. Beware of the sap, don't have any direct contact with your skin.

Those black spot maybe some damages from the spines during transport/packaging, or some insects are munching them. The yellowing part I am not familiar, possibly not enough sunlight. Sorry that I can not help much as I not familiar in keeping plants indoor, but I will forward this thread to the C&S forum, hope some other members can help.

And you have a beautiful plant there, it is blooming also

@kaktus Thank you for your kind response. You are a legend around these parts.

I will cut it tonight and see if that helps. I don't think I can hurt it too much now. It's beautiful. It was quite difficult to move. I definitely won't be doing that often.

How cold is your garage? I doubt it will handle temps below about 50*. It seems to be living in a cold dark place so stem rot is a possibility. Personally, I would leave the knife in the drawer and find a warmer sunnier spot for it to spend the winter. Have you watered since you brought it in? (Don't) Hopefully, the damage is not already done. It will either survive its misadventure or not but cutting it will not help any.

Again I am not familiar with winter and growing plant indoor.
Is the yellow circle part feel soft and mushy? If yes, it will spread.

@kaktus I believe that spot is where my dog thought it was friendly. That piece is actually hard and black. The middle appears to be trying to harden. The other spot up top is yellow with the black spot on each of the three sides. I turned the lights off for tonight. Cut the rot off. It's 58 degrees F in the garage. I can get it some light though. I'll have to move it tomorrow.