Sickly Squash Plant
We see three possible causes for your plant's struggles.
1. each summer squash plant needs about 9 square feet of space to grow to their full potential. It looks like your plant may be crowded.
2. The growing mix looks like it dries out quickly. Excessive heat and low soil moisture can quickly stress plants (of course, no problem with rainfall now!) You may want to fertilize your plants if they have not been fertilized, especially if it's a relatively new garden low in organic matter.
3. The bleaching of the leaves indicates a possible spider mite infestation. The web page has lots of information on management of the problem. Please closely examine the leaf undersides with a magnifier for signs of spider mites.
It's not too late to plant a late crop of summer squash. jt