Indeed, you're lucky it's as healthy as it is, appearances notwithstanding. Why are you not watering it? When it doesn't rain for a while, give it some water. It's a Trichocereus pachanoi, and the lighter brown parts are sunburned, the top of the tallest piece is rotted (but that seems to be arrested). For aesthetic's sake, I'd cut off the unhealthy portion entirely. You don't have to, of course, it would just look better.

thank you for your reply! where would i make the cut? what do i use to cut it with? a sharp knife? sorry, i'm just clueless about it. i will water it when its dry, how often should i water it? once a week, once a month?

thanks!!

also, could i lop off the top piece from the main stalk and put it in a shoebox for 2-3 weeks and replant it? i mean, is it worth doing if the top has rot on it?
thanks!

I meant to mention, great handle - I'm watching a bunch of taped episodes and it comes up.

You can use whatever, a garden knife, a machete, a katana, a scimitar or some secateurs, just make sure they're clean.The cuts, when made, should be on a downward bias and left to dry

No, I would wait until spring to make the cut to make a new plant (it's best to do so when times of growth are optimum), but absolutely, you can do that at whatever point on the plant, just make sure you try to make the cut at a segment's joint. Yes, it's worth it, as almost any piece of living tissue, nurtured correctly, will grow a plant, you just want to do so at the best time.

You may be also interested to know that this cactus's extract was one of more than a few used delivered suppository-like by Incan shamans to have their visions.

And watering it once every two weeks in winter, if it's dry, and once a week in the summer, if it's warm and dry, isn't too much - it looks like your soil's drainage is OK, so that shouldn't be too often. This plant can grow like a beast if the conditions (warm, sunny and wet once in a while) are good. You can have a fence of it in a few years, although there are other species that are better to use for living fences (Lemaireocereus marginatius / aka Mexican Fence Post Cactus) comes to mind.

Here is a link that might be useful: Hey! This Has Got Canadian Content, Eh

wow, great info! and the great mystery as to why my friend toted this cactus around with him all over the country to bring it home is finally solved, a ready source of psychadelics, which makes perfect sense for him, lol!

so i will wait until the spring to cut. i'm thinking i might plant new plants into pots so i have better control over their living environment. also, i don't really want a living fence of it where it now lives.

thanks so much for the great info which i'm sure i'll have forgotten come spring!!

enjoy the show, it was epic!