May or may not be the same thing.

This is a Zucchini.

This is the second (third?) I've had develop some sort of problem...leaves turning yellow; not sure it's really a wilt since they don't droop much if at all. Others remain healthy.


And looking close to the base, not right at ground level but up near where all the stems diverge it feels soft.

Is this the infamous SVB? Or just a fruit that rotted off?

By the way, think my soil has some worm castings in it?

That stem looks like it might have borers, but they would cause leaves to wilt during the day. Try getting one of the Rodale books on insects and disease control. I bought a lot of used garden books on the web for reference. From cross referencing between the pictures and the books, if the leaves are yellow between the veins and have purple spots on the undersides, they might have downy mildew. Squash bugs, whitefly or mites can also cause yellow leaves.

For borers you could use injectable nematodes (Gardens Alive has these), try digging them out with a knife or just pour gasoline over the whole thing and set it on fire (it won't save the plants but it might be satisfying to hear those borers sizzle).