...when potted plants are brought indoors in the fall.
I cleaned all of the scale off of my curry tree and kaffir lime trees - burned a lot of the leaves, using a combo of sulfur, oil, and pyrethrins, but it killed them all. I hosed them off, once they all seemed dried up, and in a few weeks have not reappeared. And when I trimmed them all severely, I did not see a single one, so it seems safe now (I never had a scale problem outside, KOW).
I repotted the small lime tree, and in the upper 3 in. or so of mix I added about a cup of DE, hoping that would help with most insects. And I have been thinking of making a mix of some herbs/spices, such as hot peppers, cloves, rosemary, coriander seed, lemongrass, garlic (this is about everything that I remember having seen in natural insecticides), and watering occasionally with a diluted mix of the strained solution (and maybe before bringing inside). Does this sound plausible, or do you have any other ideas?