White on stems of seedlings?

[Gobig_or_Gohome_toms]

I have noticed this happening on my heirloom seedlings the last few years and they seem to not be doing very well. Is this fungal and is there anything I can do to save them? The hybids I am growing (big beef and Sungold) are not showing any signs of this. Wondering if this is the miracle grow after transplanting or something else. Is there anything I can do to help the seedlings like a weak hydrodgen peroxide spray? Note I have been letting them dry out in between waterings and just watered today.

Craig