What a lovely garden! I’m sorry about your squash. :(
Butternuts are (mostly) immune to SVB’s. Especially if started early enough to really get a good ‘running start’ prior to the emergence of the SVB’s.
They do take much more room than ordinary yellow squash and zucchinis though. You can trellis them but they lose part of the resistance if you do that because they can’t put down roots at each leaf node along the running vine part.
If you’ve got someplace to let them run (mine run in my yard and I just weedeat ahead of them to give them an easier time of it) and depending on the length of your growing season you might try regular old waltham butternut or seminole pumpkin. My squash and zucchini plants are always SVB magnets. When they get afflicted I pull them up and burn them and replant.
YMMV.
I grow 500-700+lbs of winter squashes every summer. Organically for the last couple years. C. Moschata (the family that butternut is in) is the one that’s ‘resistant’ to SVB’s. If you go to the rareseeds site (baker creek) they will list the variety in the description of the various winter squashes.
If you want a c. moschata type ‘summer/zucchini’ squash try ‘tromboncino’(sp). You can eat those like summer squash or zucchini when they’re young and when allowed to mature they’ll keep long term (several months) just like regular winter squash.
Lovely little garden patch, BTW. Ants took over my geraniums this year and I eventually gave up. There’s something about those particular containers and ants.
Leaves that yellow at the bottom are a common issue here. We pull them all off and destroy them, since soil borne problems are not unusual.
Sometimes yellow leaves mean a shortage of nitrogen, or one of the trace elements/minerals.
There’s just so many things it could be, it’s hard to pin down. I usually check for aphids and bugs first. Then I pull off the yellow leaves and give it a good dose of fertilizer, and watch to see if it recovers.
If hubby has to use an insecticide, he uses one that is dispersed by morning, so that it won’t hurt the bees, and he won’t use it on anything once blooms are all around. I just stick to pepper/onion/garlic mix.