Could be from water droplets that were on the leaves and then got really chilled overnight.

Don't fret about it unless you see rot on the stems -- that's an indication of serious issues.

It's not just air temperatures (above 75 F) that are appreciated and needed by tomatoes, it's also warm SOIL temperatures (ideally never plant tomatoes outdoors until your garden soil is no less than 65F at the 4-inch depth.

Your 'maters will recover just fine as we head into the more tropical warmth of May!

Thanks for the information, Gusolie. I only lost one plant, so you were/are totally right. They are all okay and actually doing great now.

Oh, and I am not putting any tomatoes or cucumbers in the ground until very late April ever again:-)