Expert: Maureen - 6/30/2010

Question
QUESTION: Hi, I have a little fairy castle cactus that has a brown what I assume is rotting area on one of its stems. It's a small spot in the middle of the stem, and doesn't appear anywhere else on my whole cactus. What should I do?

I have attached a picture of the affected area. (I have more pictures that are zoomed in a bit more, if that would help...)

ANSWER: Dear Sara,

A closer picture would be good.  In the mean time take it out of the pot and look at the roots to see if there is rot below the soil level.  Tt looks like you might be able to save it by cutting off that branch, but you can't tell till you  do cut it off, look at the roots and determine how far the rot has extended. It's fine to leave it out of the pot for awhile.  If you can send a picture let me know.  It is important to get it out of that soil, tho, and throw the soil away.

maureen

---------- FOLLOW-UP ----------

QUESTION: Yeah, I looked at the roots and didn't see anything unusual. It appears to be just isolated on that one part of the one stem. I'm just not sure how it got there or what caused it... I'll try cutting it off and changing its soil.

Attached is a closer look at it. maybe you can determine what it actually is... It's not moist or squishy or malodorous. It's kind of dry and flaky, actually.

Thanks.

Answer
It's good that the roots look healthy.  it's important that he rot hasn't extended to the next stem.  You need to cut with a sterilized knife (I use an Exacto) that I sterilize with rubbing alcohol before each cut.  You need to get to completely rot-less (for lack of a better word) tissue i.e. white/pale green with no areas of discoloration. I'm not sure you're going to be able to do that and leave a plant that's able to stand on it's own because what you don't see is usually much more extensive than what you do see.  If successful, brush the area with Rootone or a fungicide and don't water till that area has calloused.  The cut out area won't fill in, but hopefully new shoots will develop. If the rot is too extensive you could cut above that area and start a new plant.  I've written about that in other answers.

As for why rot starts:  Who knows?  Even a tiny insult to the plant can let fungus and /or bacteria enter and cactus are very prone to it. It's also caused by over watering and by root mealybugs. I usually change the soil when I buy a new plant unless I know the grower and never water a repotted plant for at least a week after repotting.

Let me know how you make out.

Maureen