Both Bt and spinosad degrade in sunlight so it needs to be applied near dusk. I recently read(somewhere?) that eggs are sometimes deposited on stems and leaves--this was the first time I had ever heard of that. No matter what bug you're going after, spinosad should not be sprayed if bees will be visiting before the spray dries. Next year, I plan to plant Blue Hubbard squash which has been suggested in other threads as a trap crop since the borer prefers it. I also plant yellow squash at 3 week intervals to maximize the chance of actually getting some to eat.

I inject it. SVBs can and do lay eggs below the soil line and everywhere else though they prefer to attack the base. Just found lots of eggs on my cucumber plants! I inject every week. Did it last year and no borers.

I am still a little bit squeemish but curious about injecting it. Do you inject the concentrate, or dilute it to spray strength?
Wonder if it kills existing borers.

I injected BT into a zucchini plant this year that had that telltale frass near the base. I mixed up some BT, cut a small notch above the frass and basically filled the whole stem with it. I poured the rest of the BT into the surrounding soil. A few weeks have passed, and the base of the plant seems to be healing. The plant had been getting a bit droopy from the borers, but has since perked up and looks great. I have been using spinosad on my kale, and it has done a wonderful job controlling the nasty larvae that were feeding on them. Virtually no holes these days.

Here is a link that might be useful: My Unplanned Garden

I have borers this year...I don't know if it's the first time I've ever had them, or if I didn't previously know what to look for.

I tried injecting Bt, but even though I understand that zucchini vines are hollow, I can't find a space in the main vine that will let the liquid out. I've tried to come straight in from the side, and I've tried to come in at an angle. I've done my best to position the tip of the needle near the middle of the vine.

Since I can't get any liquid into the main stem, I've injected into the splits in the vine where I see the frass, and today I tried again with injecting into leaf stems above the split.

Am I missing something? Is there some trick to getting the injection to work in the main vine?