I have a Delicata squash that is yellowing and looking sickly, growing between two thriving ones (butterstick and butternut) ... any suggestions?

My only thought is that it might be too hot here for them.

1 - They aren't wilting, just looking wierd and not putting out many new leaves or flowers.

2 - No sign of squash borers (no frass, no wilting)

3 - No excessive numbers of aphids or ants (all the plants have about the same number of ants and aphids, and the others aren't sickly)

4 - With humidity of 10-15%, I doubt it's fungus.

5 - They are growing next to thriving squash, well-watered with a drip system, got the same fertilizer and soil treatment as the healthy neighbors.

www.flickr.com/photos/38617480@N07/3630712332/

and

www.flickr.com/photos/38617480@N07/3630712328/in/set-72157619569769890/

I'm tempted to yank it out for the compost heap and plant something else.