Say No to “Preventive Treatment”
When I see people spray all their trees and shrubs with dormant oil or apply a white powder of dubious origin on all their vegetables, I find them terribly pessimistic. They expect to have problems. As laid-back gardener, I never expect to have problems. On the contrary, I am always amazed when I have them! I specifically choose plants that like my conditions and are naturally resistant to insects, disease and drought, trying to create an ecological balance where plants take care of themselves and where problems are rare. So rare that my first reaction is to grab the camera for a photo of the infestation rather than carry out a treatment.
My suggestion? If you have the same problem year after year, yank out the plant in question, as it is obviously not happy under your conditions. Instead grow plants that do like what you can offer and you’ll see your problems disappear!