It sounds like you are doing all that you can! Are your plants wilting heavily during the day, come back some by morning, and are dying from the bottom up? It could be one of the wilts too! In either case, there is little more that you can do, that you aren't already doing.
I also have some wilt in my garden this year from all of the rain and cool temps. I have lost all but one of my canteloupes, and at least one tomato plant. My cukes are showing signs also, and I have been using Serenade the last couple of days myself!

Ron
The Garden Guy
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What you have done may well be the best you can do this year, but since you have these problems now that does indicate a soil related problem. Start now to make plans for next year that can aid in lessening these problems by contacting your county office of the Purdue USDA Cooperative Extension Service about having a good, reliable soil test done to learn what your soils pH and nutrient levels are and what needs to be done do balance those and also dig in with these simple soil tests,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to see what else your soil may need.

Here is a link that might be useful: Purdue CES

Thanks for the feedback. Not sure if it's a wilt or not. It hasn't hit anything but my tomato plants. The squash are getting killed by the bugs, which is odd since I've only been able to spot one adult on the plants. So far Serenade hasn't helped much, but it's only been a couple of days.

I've been planning on getting around to a soil test. This is the 2nd year for this garden. I made it with a mix of compost (mostly cow manure with some chicken and peat mixed in) and peat moss. It's a nice dark, fluffy mix, but there are very few earthworms present. Not sure why, but my house was only built 3 years ago and it's on a former corn field, so I assume the area's still recovering from the pesticides. The garden itself is raised 1 feet up.