Issues in Choosing an Insecticide For Scale
The problem with scale insects is that their shells protect them from conventional pesticides that kill on contact. Therefore, since they are usually at this stage when they become visible on plants, pesticide options are limited. Light horticultural oil which smothers scale or a pyrethrin and insecticidal soap product which permeates their shells and then kills on contact are the best choices if handpicking techniques do not control scale infestations on your plants. Repeat sprays may be necessary as new generations of scale hatch and become visible over the growing season. Use these products as treatments; they are not effective as preventative sprays.