My neighbor's zucchini patch got hit first, so I was on high alert. When my plants started drooping, I knew right away it was borers. I didn't have a syringe, so I used a small knife to make a slit and brushed Bt powder inside. It was messy, but it worked. I remember reading online that you have to act fast before they damage the stems too badly. Actually, one plant was too far gone and I lost it, but the others bounced back after a week or so, and now I check the stems every morning for that sawdust-like stuff, just in case.