Iowa Insect Information Notes

Houseplant Scale Insects

Houseplant Scale Insects

Scale insect on Ficus sp.. Adult scales are black and to the left in the picture, immature scales are beige and to the right. Actual size approx 5 mm.

Several species of scale insects commonly infest plants in the home or greenhouse. These sap-feeding insects have a tan to brown shell-like covering or scale that protects the insect's body. Scales may be from 1/16 to 1/4 inch in diameter and are usually found on the stems and/or leaves. Some scales are hemispherical in shape, while others are oval and flat. Scale insects feed by sucking plant sap and may cause poor, stunted growth. Death of infested plants is possible in severe cases. A large quantity of a sweet sticky liquid called honeydew is excreted by scale insects. Honeydew can make a sticky, shiny mess on the plant and nearby furniture and floors. A black fungus called sooty mold may grow on the honeydew.

Scale insects are difficult to control. There are several well-known remedies that can be tried in an attempt to eliminate scales from a houseplant. However, there is no easy, simple cure for a scale infestation. One possibility is to pick off individual scales or gently scrub (or rub) the scales loose from the leaves and stems. This is a laborious task that works only on small, large-leafed plants. Dabbing each scale with an alcohol-soaked cotton swab is another possibility on lightly infested plants.

Sprays can be used for scale control. Success will depend upon thoroughness and persistence. Insecticide sprays (aerosols or hand pump sprayers) made just for houseplants are available at garden centers. You can use a mild dish washing detergent in place of the commercial insecticide soaps. Use a dilute solution of 1 Tbs of detergent per quart of water. Soap sprays can be applied with a sprayer or used with a soft cloth while washing infested leaves and stems. Insecticides must be applied thoroughly, repeatedly and persistently (weekly for a month or more) to get good control.

Granular insecticides that you add to the soil of infested houseplants seem to have very limited effectiveness and their use is discouraged because of toxicity concerns. On those plants that regrow after pruning, removing the heavily infested stems and treating the remainder is a possibility. Finally, unless the plant is particularly valuable, many people find it best to throw away infested plants before the pests spread to other houseplants.

Updated 07/14/2005 - 1:50pm