Upon first sighting, scale insects are often mistaken for scabs or bumps on a plant's tissue. There are many different varieties of scale insect that attack ornamental plants, and all of them are immobile during their adulthood. When they are nymphs, they crawl to a spot on a leaf and suck the fluid out of it. Small infestations of scale insects do little damage to plants. But a heavy infestation can yellow a plant's leaves, stunt its growth or even kill it. Luckily, these small, immobile insects are quite easy to get rid of.
Use a pair of sharp, disinfected pruning shears to prune any plant tissue that is heavily infested with scales. This works best for localized scale infestations. Disinfect the pruning shears after you use them and bag the plant tissue and throw it away.
Mix 1/2 teaspoon of detergent soap into 1 quart of lukewarm water. Dip a clean rag in it and use it to wipe away mild infestations of scale insects.
Spray the plant with an insecticide prescribed for use on scale insects in spring when the mobile, soft-bodied scale nymphs are active. Spray to the point of run off, and concentrate on areas where you notice activity. Re-spray as needed at the intervals dictated by the insecticide's manufacturer.
Spray adult and nymph scale insects with horticultural oil during any time of the year. Follow the manufacturer's instructions and coat immobile adult insects with the oil which will smother them.
Prune bushy plants or cull closely grown plants to improve air circulation. Scale insects need a moist and humid environment to thrive.
Closely monitor your plants in the future to spot scale insects before they do any real damage. Check the undersides of leaves and stems roughly once monthly.