Ever try plain old Diatomaceous Earth? This is something that lots of folks use on plants for the soft insects. I put it in water and spray it on my tomato plants because it is so fine powder that it should not be breathed in. It dries to a whitish film and cuts tiny holes in the insects so they dry out and die. I also used to put it in most food for my dogs for worms. It's also used for an insecticide and in cat litter. A very useful thing.