My plants are very healthy but, I constantly battle mealybugs - there is no such thing as complete eradication. And yes, a bad infestation will kill a plant, it has nothing to do with the original health of the plant.
I don't bother to dilute or add soap to the alcohol but I do blast the bugs off with my sink sprayer or garden hose for two reasons: First, to get rid of the alcohol so my plant won't be damaged but the second bigger reason... without the alcohol present, more mealybugs will crawl out of wherever they were hiding so I can spray them too. But, if you don't get rid of the mealybugs hiding in the crevices of your pots, you will never get them under control. If your plants are sitting on porous surfaces, you will have to kill the mealybugs hiding there as well.
All I can think is NYC mealybugs are much better behaved and less resilient then what the rest of us are dealing with.
