They would eat holes in leaves and cause localized yellowing. Sometimes they can cause a wilt disease, but then along with yellowing, your leaves would be very wilted.
examples of squash bug damage:
https://www.omafra.gov.on.ca/english/cro ... 031f11.jpg
https://s3.amazonaws.com/plantvillage/I'm ... 1380225158
What you have is nutrient deficiency. The fish emulsion you used to "condition" the hay was very much less concentrated than the fertilizer described in the article I linked. So your hay was much less conditioned, I.e. less broken down, less nitrogen and other nutrients released.