The borers are hatched from eggs laid by moths on the plant. They fly in and land on the plants to lay eggs.. So putting black plastic isn't going to help in any way.

If you search most any of the 100's of discussions here about how to prevent SVB the one recommendation they all have in common is row covers. If the moth can't get to the plants to lay the eggs then you don't get any borers. But you do have to hand pollinate.

Dave

Even common advice to cover base of the stem doesn't work - they successfully start their damage in the middle of the vines too.

The other recommendation is to grow resistant varieties, like butternut. But searching the other discussions will give you loads of info.

I'm linking, below, a particularly good discussion from last year.

Here is a link that might be useful: SVB routine

Just dusted heavily with diatomaceous earth including under leaves and stacked straw up the sides of the plants. I noticed one had entered the stem and i made a thin mix of water and diatomaceous earth in a cattle syringe and injected the entry and stems throughout . This product is completely harmless and food grade and I had pretty good success last season. Also when preparing next season look for cocoons in your soil as you till and squash that darn thing!

Trombocino seems to be resistant. I also let my squash grow across the ground and cover stems with some dirt.
SVB isn't much of a problem but I've had a few. Squash bugs are bad here.
Using a fabric cover can prevent both but you need to uncover to pollinate.

Thanks, ElisaZ5. That was definitely a good collection of scenes from the SVB battlefield. I agree that your best bet is covering the plant with insect barrier from the beginning. I think I've dodged the bullet so far because I haven't grown any squash except one volunteer Halloween pumpkin a few years ago that did fine. They don't seem to bother cucumbers, cantaloupe or water melons. But I plan to grow yellow crookneck this summer and I want to be prepared.

By the way, I don't see how diatomaceous earth would help since insects need to come in direct contact with it and it is inactivated by moisture. The larva probably go straight from the egg to the inside of the stem. Injecting BT or spinosad sounds like it would be more effective once the eggs have been laid.

Ohiofern, sadly they will go after cucumbers. I found eggs on mine very early last year. I picked off the eggs, covered them up and once the plants got bigger and I removed the cover, they left them alone. But my first year gardening they went after my mature cucumber once I pulled all my squash. I found several in the stem when I pulled it out. :/

It's not their first choice, but do keep an eye on cucumbers when young. I have mine covered for now and will keep them covered along with my squash as long as possible.

Last year I used tulle, which kept the borers away, but the plant self-fertilized and I got some strange but edible fruit. I guess if you have LOTS of plants under the same cover it might work better.

This year I'm trying to paint the stems with Sevin. Yep, with a 1" paintbrush. It's easier than it seems, because you just paint the real vine stems, and not the stems going to individual leaves. It can get a bit confusing, however, if things are tangled. That way, you keep the Sevin off the fruit and flowers, and even the leaves, unlike if you sprayed or dusted. You put the stuff exactly where the bugs are headed. I do it once every couple of weeks. No problems yet.

Summer squash are super easy to grow under cover since they plants are smaller. Once your female flowers open, you can either hand pollinate and re-cover, or just let nature take its course, but by that time youd have a good harvest already. It probably is at least 3 weeks from the time the eggs are laid until you would notice any damage at all.

Mine all made it to the end of the season last year, aside from the one I snapped in half (doh :()

I injected BT when i first saw signs of borer holes. All of them had some injury, but most had their stems still intact. This one, I must of missed a borer.

But this plant, while weakened and dealing with powdery mildew, still was producing to the end of the season. Even with that much damage on the stem. Kind of amazing.