Neem oil is a popular way to try to kill scale, and is an organic, pesticide-free way to treat the infestation. You’ll need to thoroughly spray the plant weekly until the infestation is gone. Keep in mind that in heavily infested plants may be near impossible to remove the infestation and it may become necessary to get rid of the plant to save the rest of your plants. Also, even when the scale insect sie they may not release from the plant so if you still see them there, it doesn’t mean they are alive, if nudged dead scale insects will easily fall off the plant.
Continue to use the neem oil weekly for 1-2 months until you are sure the insects are dead.
Here's a very detailed piece on it: https://www.planetnatural.com/pest-problem-solver/houseplant-pests/scale-control/
Hi Miira: Here is a site that may help. You have to scroll down past the blah, blah, blah to get to the meat of the article. Why they do this is beyond me, just get to it! :)
We like to use cinnamon and cinnamon oil to deter insects from houseplants: https://chemistrycachet.com/things-to-use-cinnamon-for/
Thank you all! I hate to end up throwing the plants out. And I like the natural solutions because I have pet birds.