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My small lemon tree has been showing these scabs for a while. They are brown, mm sized, and fall off very easily just touching them with a finger or a nail. Examining the soil with a lens I also noted some tiny white mites, but they don't seem to climb on the plant and neither produce any web.
I've been using a generic insecticide but I didn't note any improvement. Sould I try with some water+soap solution as suggested here: What is wrong with my lemon tree?