Problem type: Insect

Name of problem: Mealybugs

Plant name(s): 
Flowering and foliage house plants

Symptoms / Characteristics:
The most obvious symptom of mealybug infestation is the presence of a white, waxy fluff on the leaves or stems. Mealybugs pierce succulent plant tissues and extract the sap causing leaves to turn yellow, wilt and drop. Severe infestations can result in stunted or distorted growth and eventually plant death. Like many other sap-sucking insects, mealybugs excrete a sticky substance known as honeydew that can facilitate the development of harmful sooty mold fungi. The honeydew may also attract other types of insects, especially ants. This may be of particular concern to gardeners who keep house plants outdoors during the summer.

Mealybugs are extremely small (less than 5 mm) and may be difficult to detect. Their pinkish oval-shaped bodies become covered in a white, waxy, thread-like substance once feeding commences. The presence of this white fluff is often used as a diagnostic tool to identify either mealybug feeding colonies or egg masses, which are coated in a similar substance. The slow-moving mealybugs may be found anywhere on the plant but generally prefer the succulent tissue within leaf axils and beside leaf veins. The ground mealybug, as the name suggests, resides in the soil and sucks juice from plant roots.

Control / Preventions:
Sticky, shiny honeydew on plant leaves may indicate an infestation of mealybugs, aphids, scales or whiteflies but the presence of white fluff on the leaves will help to distinguish mealybugs from these other sap-sucking insects. Control is often difficult as the insects are easily concealed and protected within the leaf axils. Infested plants must be isolated immediately and must remain in isolation for at least ten days after a control has been administered. Plants that are insect-free following this critical period can be returned to their original location.

Small populations of mealybugs and egg masses can be removed manually. A cotton swab or fine paintbrush can be used to dab rubbing alcohol directly on the insect. The alcohol will penetrate the waxy covering and effectively kill the insect but extreme care must be taken to avoid contact with plant tissue. If accidental contact is made, wash the affected tissue within five minutes to prevent desiccation.

A strong stream of water may help to reduce mealybug populations. However, applying too much pressure will only cause additional injury to the plant. Washing the plants gently with warm, soapy water may be a more effective treatment.

Heavily infested plants may require a foliar spray of insecticidal soap or other recommended house plant insecticide. Thorough coverage is essential in order to ensure that insects within leaf axils or on leaf undersides do not escape treatment. Female mealybugs lay hundreds of eggs at a time and a single missed female can repopulate a plant.