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A. First of all, there are several different kinds of scale that attach different plants, such as tea scale, euonymus scale, cottony maple, and several others, but what they all have in common is they such the lift right out of our plants. We are often not aware of the problem until the infestation and damage is extensive or we may apply insecticides at the wrong time.
Scale weakens or kills the plant by sucking plant sap through piercing-sucking mouthparts. While feeding, some types of scale give off a sweet, sticky substance called "honey dew", which drips down on the lower leaves and attract ants and flies. Fungi often grow on the "honey dew", giving leaves a "sooty" appearance. This is called sooty mold. Mature scale never move once they firmly attach themselves to branches, twigs or foliage.
Scale Control: Parasites and predators such as small parasitic wasps, ladybird beetles, other insects and some fungi can attack and significantly reduce scale insect populations. You should delay insecticide treatment in instances where there are only a few scale insects are present and there are many lady beetles are present, or if there are many dead scale with tiny holes which indicate parasitization by small wasps. Insecticide sprays may reduce or eliminate these beneficial insects.
The key to controlling these pests is to closely examine your plants to help keep the scale population to a bare minimum. If the scale population becomes too overwhelming, treat them with insecticidal oils during the dormant season (not actively growing) or with summer oils in spring and summer. Make spring and summer applications when the young larva (called crawlers) are actively moving over the plant. You will need a magnifying glass to see the tiny, pale-yellow scales which move outward and upward on the plant to the most recent growth. Make sure to treat the surface and the underside of leaves for effective control.
Mealy bugs and scale can be controlled on houseplants by swabbing exposed insects with a diluted soap solution (for example, mild dishwashing detergent) or rubbing alcohol. If scale is dead, they will be dry and hollow and flake off easily. Be careful when spraying valuable plants as phytotoxicity or spray burn is always a possibility when insecticides are sprayed on plants.