Just wanted to share my success story. It's only been 3 weeks, but so far I seem to have the upper hand. For the past 3 years, I've been unable to grow summer squash because of vine borer damage. Well, after reading a number of threads on bt injections, I gave it a try. AND... It's working! For now anyway.
On or about May 12, I detected the first signs of SVB damage. Prior to this, I scrubbed away tiny eggs, mounded dirt around plants and kept close watch for the wasp-like adult. I did this EVERY single day! I have 10 plants, 3 zucchini and 7 crookneck. Somehow, I missed the eggs and my plants were infected anyway. I mixed a few drops of BT liquid in 16oz of water then used a 1cc syringe to inject plants. I tried a much larger syringe (the kind with a point, but no needle) but with no success. The liquid would not penetrate. I switched to a much smaller 1cc syringe (leftover from pet meds) and injected a half syringe a few inches above each hole. I injected a bit more here and there for good measure, including uninfected plants. As a final layer of protection, I covered the base of each plant with Dipel dust and have continued to do so after each watering. So far, it's working! Hurray!! I'm not recommending this method, just sharing my success. If you have had success with another method, please share. So far, I have not had to inject plants again. Aside from a magnesium deficiency in the zucchini, my plants are doing well.
Two things I'd like to mention here. First, my plants had not yet set fruit, so I was really surprised to see SVB damage so early, but I believe this is why I always missed them in prior years. I waited too late to check plants. I never had success digging out or cutting through vines. Plants always died anyway. Also, the warning sign was a little different this time. As in the past, my plants wilted. However the infected plants wilted eeeever sooo slightly. It was barely noticeable. I only noticed because I had been checking plants daily. As of now, no more wilting, lots of fruit and my lovely little bees are safe. I never dust in the morning when bees are pollinating.
Here is a link that might be useful: SVB Thread