Interesting thread, about a common pest for those of us in the eastern 1/2 of the U.S.. Those of you further West, count your lucky stars that SVB hasn't reached you - yet.
SVB are very bad in my area; without some type of prevention, losses for
C. maxima and
C. pepo squashes would be nearly 100%. Under normal conditions, my default method is to start squash as transplants, and cover them with floating row cover immediately after transplanting. The cover stays on until flowering begins, which in my area, usually occurs when the SVB egg laying period has passed. This has not only prevented SVB, but usually prevents infestation by the first hatch of squash bugs & cucumber beetles as well.
This year was
not a normal year. Near-record rainfall kept me from putting up the covers in time. When the garden finally became passable, there were already large numbers of eggs visible on the stems. The weather also resulted in adult moths being active - and laying eggs - later than usual, well into July. I sprayed Neem on as much of the stems as I could reach, re-applying several times.
A few weeks later, frass showed that some eggs had survived, and some wilting had begun. I considered using the BT injection method, but garden stores nearby were out. So I got the idea to use a battery-powered water pick, in an effort to wash out the frass, and hopefully flush out some of the larvae. The water pick holds very little water, so I had to lengthen the pickup hose, to use a larger water reservoir. It worked!!! Quite a few larvae were washed out; I then sprayed Neem into the now-open holes, to reach any larvae still present. It has apparently worked - the plants which had begun wilting still do on hot days, but have not deteriorated further, and wilting has not appeared on the other plants.
While floating row covers will still be my preferred method of preventing SVB, I like the idea of BT injection, and may try that in the future. The use of high-pressure water jets, though, is another alternative to rescue plants already infected. While I used a water pick, a pressurized sprayer might work as well.