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How to Get Rid of Scale Insects


Scale Insects on Plant

Scale Insects on Plant

Photo: © Marie Iannotti (2008) licensed to About.com, Inc.

Scale are tiny parasitic insects that adhere to plants and live off the plant’s sap. They look like bumps and are often mistaken for a disease. There are some 7,000 species of scale insects, varying greatly in color, shape and size, usually ranging from 1/16 - 1/8 inch.

Scale are usually divided into 2 groups: soft scale and armored scale. Soft scale are covered with a protective waxy substance and are somewhat easier to kill than armored scale, which secrete a hard shell over their bodies for cover. Mealybugs are also part of the scale family.

Scale eggs are laid under the female’s body. They are called crawlers when they first hatch, because the nymphs have legs at this point and crawl off to find their own spot to attach and feed. Control measures are most effective during the crawler stage.

Different species favor different plants. Plants frequently infested with scale include: Euonymous magnolia and fruit trees and shrubs

Control of Scale

  • Outdoor Plants:
    • Treat with dormant oil in late spring, just before the leaves unfurl. Scale can overwinter as nymphs or eggs tucked away in tree bark.

    • If you catch the problem early, pruning infected branches is often the easiest and surest solution.

    • Scale are preyed on by beneficial insects like soldier beetles, lady beetles and parasitic wasps.

  • Indoor Plants: Remove scale by rubbing gently with a facial quality sponge dipped in rubbing alcohol. The alcohol alone should kill the scale, but the dead insects will remain on your plants and make it difficult for you to scout for new infestations. The small facial sponges, found in the cosmetic aisle, are abrasive, yet soft enough to use without scraping the plant stems.

    Be sure to buy plain sponges, without cleanser or lotion in them. As always, test on a small area first, since some plants are more sensitive than others.

I mistook the orange spots on my plant for rust, but when I couldn't rub or hose them off, I knew it was scale.
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