I've got two kalanchoes that have scale bugs on them. Initially, I tried spraying them with neem oil, which seemed to reduce the population but never eliminated them. One person I spoke with said that remove the adult scale bugs when they form the "scale" is the best way to get rid of them, as they are easy to remove and that will prevent them from laying eggs for a new generation. I've been trying that for a couple of months now (checking them almost daily), but the plants seem to be slowly getting weaker and I still see new scales forming. :(
Another suggestion I got was a bit more drastic: submerging the entire plant (including pot and soil) in water for 24-30 hours. The idea is that the scale bugs can't survive that long without air and they'll all die.
I've never tried anything like this so I'm wondering: does anyone here have experience with this technique? I'm a bit skeptical it would work and I can't find much to support or refute this suggestion. I'm hoping someone here with more experience might know if this is a good idea.
Since these are kalanchoes that propagate easily by cuttings put in water, I was just going to cut them off at the base and throw away the soil and just submerge the cut stems.
As an aside... The original scale bugs came in on some spider plants that have been going outside for a few years now, and probably picked them up outside. By this point in the late summer, they look fine outside (probably some insects eat most of the scale bugs), but by late winter, they start to get nasty looking. Interestingly, the scale bugs never seem to cause serious damage to the spider plants, they just look bad. If submerging is a good way to get rid of scale bugs, I'll probably try that with the spider plants too.