Question
I have what I believe to be a Trichocerus peruviana that was given to me by a college roommate as a gift.  I am not sure if it is healthy or not because it is developing discolorations and a black spot.

Last year, it also had tiny larvae on it that seemed to be giving it black spots and other trauma.  I killed them by misting the surface with vodka once a day for a month.  I prevented the vodka from entering the soil because I assumed that would harm the cactus.

Shortly after I killed the bugs, the top of the cactus turned black and squishy, so I measured two inches from the black spots and squishiness and cut the top off with a sanitized kitchen knife (using sanitizing techniques adopted from homebrewing).  The cactus seemed to heal well and it grew a new arm off the top and a short stubby arm off the bottom.

It is now ~32 inches tall above the soil and it is in a 14" diameter unglazed earthenware pot filled with 'cactus soil'.   It has a black spot on the very top.  No larvae are apparent.  It has a number of old scars and small spots which have turned bone-white. It has some striations and other discolored spots, particularly at the top where the new growth arises from the cut.  Those spots range from light green to a golden-brown color and they are rather plentiful.  The flesh of the cactus is uniformly firm and about 80% of it is a healthy green color.  I water it about every 6 weeks in the winter and about every two weeks during the warmer months.  It has never been fertilized.

Do you think my cactus is healthy despite the persistent problems with spots?

Is there anything I should do to improve the health of my cactus?

Thank you,
A H

Answer
AH,

I'm not sure why your plant continues to have issues at the growing tip, however, I would like to see a picture of the plant just to make sure it's not something else wrong. Both times your plant had that problem, was it following winter? If you can, please send to: [email protected]

Thanks.

Sincerely,

Greg