Not sure where to post this, but this forum should be close enough.
I have a bunch of seedlings that I started indoors. I try to grow them to about four to six leaves and then transplant them outside.
For some reason, some seedlings promptly die upon transplantation. Peppers seem to be particularly prone to that, I lost a third of one batch to the same problem. After transplantation, a section of the stem quickly dries out, thins and turns brown. The rest of the plant dies because nutrients no longer can reach it.
It does not look like root damage to me. Any idea what it could be? Pests? Some kind of chemical in the soil?