Not stem rot. So what the f*** is it?

It starts as a discolored, slightly sunken band around the stem, near the top of a plant or branch.
A knuckle forms right at the site and as it swells, the band sinks further into the stem, tightening, until after a few weeks it eats all the way through. The top will eventually fall off, leaving both edges brown, dry, and dead.
The top thrives, right up until it falls off. The bud above the affected area is as full and as far along as the rest of them.
Here's a pic..

Hard to tell from so far away, could be a cut worm, do any of the branched show damage?

Nah, I've had cutworms before..they bore a ahole in the stem and tunnel, leaving behind mounds of residue.
The only thing out of the ordinary this grow was a lack of water. I could only get to them once, sometimes twice a week. could that have anything to do with it?