The stems of most of my young tomato plants appear to have developed cankers - it almost looks like collar rot - just above the soil level. The plants themselves are still growing and look healthy. Any idea what this is? These plants need to be put potted up asap - or thrown away, if this is going to become a larger problem.

The cankers are on a Hillbilly and several other varieties. They're in 5-1-1 mix or high quality potting soil. I noticed it right after I'd watered with fish emulsion, and thought at first that an animal had been chewing on them. Since then I added more soil to the pots to cover the cankers, and they've calloused over (the last photo is from a month ago), but I'm seeing new marks on the stems. p.s. these photos were taken right after watering: I do let the pots dry out thoroughly before rewatering.

There have been two other members with a similar issue. It has been said that this could be damping off disease. Since the stem seem to have recovered, I would plant them out ASAP and plant them deeper than the are now so that their stem damage has been buried. I think that the plants will be fine.
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