This is a common problem caused by squash stem or squash vine borers. They eat a hole in the hollow leaf stem or the main vine and eat the tissue inside. One thing to help prevent it is to put newspaper around the plant so the leaves and "limbs" don't sit on the ground but on the newspaper. Do a Google for "squash stem borer" and several good sites will come up. I am attaching a link that may interest you. One site calls for spraying several times before the and especially when th eplants start to bloom.

Here is a link that might be useful: Squash Boreres

Ruth, I know that you said that it's too early for borers, but it really isn't. They can be expected to appear in early to mid June. Like Terry, I can't think of what else might cause this, year after year, but SVB.

Thanks to both of you about the squash. I pulled up two plants that were about dead; I cut the stems and examined them and found no borers. I did find a pupa on the tabletop that probably dropped off. It was black striped with white and metalic here and there. The zucchini was affected but so far not the pattypan. We re-planted. WE will see what happens.
Thanks Again, Ruth

I guess I should start a new trace but I'd rather piggy back on yours. Hope you don't mind. My squash problem is different.
My squash got delayed a few weeks by all the heavy rains and my soil souring but they are growing good now. My yellow crooknecks have been blooming over two weeks but have not yet put on a single squash. My scallops are starting to bear and the zucinni have small squash not yet big enough but the crooknecks started false blooms at least a week earlier then either of them. What to do?

Tedposey, most squash (and cucumbers) put on male blooms first and about 10-14 days later they begin to have male and female blooms. It sounds like you are about due for some female blooms any day now. With female blooms you will get squash.

Thank you Tsmith. I am aware of that. Been eating zuchinni and scallops over a week now but still no yellow crooknecks. I did find squash vine borers in some of the vines but they haven't killed them. I split the vines and killed the larva and covered the vines so they will make new roots.
Found one zuchinni on a vine that was supposed to be crookneck. Lol Seeds all from Shumway.