Cutworms? You can put a collar around the stem.

It could also be rabbits.

This is the first year I have used row covers on my melon plants with great success. Immediately at planting time I covered the plants with Agribon row cover out to the edge of the black plastic. I used PVC to make a tent over the whole area.

I also planted marigolds to see if that would help.

Now I am using Surround clay spray and have zero cucumber beetles so far.

I've seen squash vine borers in my catelopes before. If its fras at the base of the stem that probably your issue. Next time you pull one up cut the stem vertically and check for them.

If you haven't already, go out after dark with a flashlight and examine the plants. If insects are the culprit, that's a good time to catch them at work.

Thanks all,

I also use surround, but my plants are so small I have wondered if maybe they couldn't "breathe" as well with it on them. Still spraying them though. Can't say there's never been a few days after a rain that they weren't covered.

I examined the stems more closely and it looks like some are split vertically (similar to a squash plant) but I do not see any frass. Other stems just seemed to have a weak spot where they just broke. The stems are all still pretty narrow at this point. At least one watermelon plant had a similar fate. I do see lots of cucumber beetles.

Thanks for the tip about the row cover. I have not tried that as I grow my 'lopes vertically on trellis, but I will have to consider something different for next year.

Hmmm, I had a couple of squash stems that split vertically a few weeks back. They lived through it and continue to grow, and all I could think was that some of our extra rain made the stems split open, perhaps? Is it possible for you to take a picture of the damaged stems?