Things are getting worse. Is there no hope?

Your leaves look like you have a problem with mildew. I get mildew every year on cukes and squash in August. My garden is on the east side of my house and I get so much mildew I could no longer grow summer squash as the powdery mildew would wipe the plants out by mid-late August.

Currently my cukes have some mildew but are doing ok. My sweet potato squash vines are dying out just like the pumpkin vines in your photo. I also have bush delicata squash and they have mildew but seem much more resistant to it.

Mildew can be a problem with rainy weather and always seems more prevalent later in the growing season. Fungicides can help but are more preventative than curative. I am too lazy to spray as I already do enough spraying having a fruit orchard.

Your ground also looks mighty wet in the photo. Does it normally drain ok?

Normally when I get powdery mildew I see the white spots all over my leaves. Not so here. And this soil is on the sunny side of the house and dries quickly.

Also I've been spraying Bifen I/T and BT on my plants every week to kill off Vine Borer larvae.

This is Downy Mildew. Spray a fungicide. Check the correct and available ones from the nearest shop. Mancozeb is one such product.

Before spraying, please remove all infected leaves and twigs, keep the ground clean. In this case henceforth, profylactic sprays are better than curative ones.