Maiden, I may be way off, but have you checked for insects?
Inspect your Scheff thoroughly. On and under leaves, between stems. Do you know what to look for? Are you familiar with plant bugs?
Scheffs are notorious attracting insects if a room is stuffy, and/or dry. Depending on the type of bug, they'll damage a plant in no time. You did say leaves were not discolored, which is the first sign, so I'm hoping insects aren't the problem.
But:
Three most common Scheff attracting insects are Spider Mites, (look for fine webbing) Scale, (brown or white bumps that can be scraped off,) and Mealy, (white-cottony patches,)

Is the black stalk soft/mushy? What percentage of leaves fell? Sometimes repotting causes shock.

Does its pot have drainage holes? Sitting in an outer/decorative container? Soil should dry between waterings, moreso if room temps are cool.

Fertilizer could be another problem. How often did you fertilize? How long after repotting did you add fertilizer?
Many soils now contain fertilizer, so is it possible the soil you used to repot with contained fertlizer, then more was added? Fertilzer burn/over-fertilzing will turn stems/trunk black.

Perhaps someone here has more to offer. For the time being, check for insects, can't hurt. Good luck, Toni

Thanks Toni, I did pull the roots out of the soil, they smell fine, no signs of bugs, like you described or otherwise. One thing I did notice in pulling it out of the soil, they sure weren't planted very deep, barely covering the roots, so I did bury it a little deeper. There is a teeny weeny littke green spot (new plant growth) just below the surface, is that a sign it's viable?

I don't think it would be a repotting issue, I repotted almost two years ago. This just started happening a month or so ago.

The pot has good drainage, I don't fertilize very often, and I don't buy soil that has fertilizer in it, I'd rather do it myself. I hate to admit it but I have probably only feed it three times in two years.

The black area is firm, not mushy or soft.

I'm wondering if I just under watered it. After giving it a big soaking the soil is moist enough to clump when I squeeze it, but falls apart easily. So, I will wait and see how she reacts to a drink. What would happen if I cut it down past the leaves? Would it grow back? And could I root the top in water and make a new plant?

Thank you for your advise, I will keep you posted.

Since it's sprouting, the plant is alive. Another way to tell is by peeling a little bark..green='s alive.

Roots should be completely covered with soil. Now that you covered its roots, let's see what happens.

If you cut back to the base, it will continue growing, but unless your Scheff looks unsightly, do you want to do something so drastic? Maybe you should wait to see how it does before butchering. Toni

If you've been growing them in the same container for more than 18 months and haven't changed anything except to give more sun, it's doubtful that it is a watering issue. Lack of light might make leaves fall, but it doesn't explain the spots on the stems, nor do any insects that I can think of. Under-watering would be unlikely to cause the symptoms you describe, and total defoliation would likely occur before tissue death in stems due to drought.

There are a couple of diseases common in scheffs grown as house plants that could be your plant's problem. Pythium splendens is a damping off disease that often comes to the hobby grower's tropical plants in infected roots or soils and then progresses upward into the stem(s). Stems, especially younger stems that are only partially woody tend to develop thin or sunken, dry, and withered looking areas on them.

Southern blight, caused by a Sclerotium fungus, is also common in scheffs. The primary symptoms to look for are a brown stem rot which eventually completely encircles the stem at or just above the soil line. (probably not this one, but it's common).

The problem is, these diseases don't respond well to fungicides. Treatment regimens are mainly prophylactic.

Al

I think I figured out what the problem was. . . but why all of the sudden? I had it in a 14" pot, gasp ! But when I put it in that pot there were two combined pots w/3 plants each. Since then (thinking back on it) one of the plants completely died and I pulled it out of the soil. Don't know what happend to the rest of them, but anyway there is only 3 stalks in this HUGE pot, no wonder it is stressed out. I did move it to a smaller (8") pot this past weekned, hopefully it will pull thru.

I can't believe I didn't notice this until now, poor thing.