Too much water or not enough nitrogen.

I know it wasn't overwatering as the day that they turned yellow everything in the garden was totally wilted since I hadn't watered in quite a while.

Would lack of nitrogen cause that in just a few plants? How can I increase nitrogen?

Check the plant for SVB.

You can give it a dose of high nitrogen liquid fertilizer, like fish emulsion. See if that brings the color back.

Thanks for all of the replies!

I went out and checked and several looked like they had holes in the stems. So, I cut them open and found the yucky SVB worms. I made sure to kill the worm and then covered the stem where I opened it with dirt. Will the plant live through this?

I also checked my yellow squash and zucchini and found a few worms in those also. I hope everything does not get ruined. They have really been doing well!

Also, in the process of getting the worm out of one of the acorn squash plants, one of the smaller acorn squash fell off. It's about the size of a baseball and is not dark green yet. Will it ripen up now that it is off the vine, or should I toss it?

Thanks!

You can eat it.