Houseplants - wonderful, living, green additions to a domicile that soften harsh interior edges, provide oxygen to the environment, and remind us of spring activity during these snowy days of winter. Proper watering and fertilization with sufficient light exposure constitutes the primary care needed for houseplants.
Unfortunately, it is possible that some houseplant leaves have curled or developed yellow or white speckles, flowers may be fading atypically, stems have died, or a sticky, shiny covering is seen on many plants and nearby furniture and floors. These telltale symptoms are the result of feeding by small and uninvited arthropod pests. Aphids, cyclamen mites, spider mites, scales, thrips, and whiteflies are commonly found on indoor plants and can produce significant damage to them. There is yet another houseplant pest worthy of discussion: mealybugs.
Mealybugs are small (1 to 4 mm long), flattened, oval insects appearing as miniature sowbugs. They are covered with white, powdery wax that resembles finely ground meal, thus the origin of their name. Many species are ornamented with filaments of wax around the margin and posterior end of their body. Mealybugs are related to scales, aphids, and whiteflies.
Although there are more than 275 species of mealybugs in the continental United States, two main species are commonly found on houseplants: the citrus mealybug and the longtailed mealybug.
The citrus mealybug, Planococcus citri, has been a recognized pest of citrus and ornamental plants in the United States since 1879. It is said that this species will feed on every flowering species grown in the greenhouse. Adult female citrus mealybugs produce from 300 to 600 eggs, which are deposited in a white, fluffy case called an ovisac. These ovisacs are commonly seen under leaves and along the stems of houseplants. Adult females have an average lifespan of 88 days.
The longtailed mealybug, Pseudococcus longispinus, also has a wide host plant range. Its name is derived from the long (3 to 4 mm) waxy filaments extending from the rear of adult females. Fewer eggs (about 200) are produced by adult females, but this species produces live young and no ovisacs are present.
Mealybugs have needle-like sucking mouthparts. Feeding activity can cause a yellowing of host leaves, distorted growth, premature leaf drop, and, with heavy populations, plant death. Mealybugs also produce large amounts of a sweet, sticky liquid waste product called honeydew. A black fungus called sooty mold may grow on the honeydew.
Four to six broods of mealybugs can be produced each year in interiorscapes. Most stages of the mealybug life cycle are mobile. These insects crawl from one feeding surface to another or from one plant to another, especially when leaves or branches overlap.
This pest is usually brought into the interiorscape on an infested plant. Therefore, one of the best ways to manage mealybugs on houseplants is to carefully check plants being considered for purchase and reject any infested plants. Quarantine new plants for 7-10 days in an isolated spot, and check for signs of mealybugs or other household pests before adding the plants to your interiorscape.
Other suggestions for controlling mealybugs include the following:
- Dabbing each insect with an alcohol-soaked cotton swab
- Gently rubbing the insects from leaves or stems
- Placing the plant in a tub or shower stall and knocking them off with a brisk water spray
- Carefully washing plants with soapy water; one tablespoon of liquid dish detergent in one quart of water is a good ratio to use.
- Spraying houseplants with a registered insecticide; active ingredients include azadirachtin, permethrin, pyrethrin, resmethrin, and rotenone. Usually more than one application is required to get good control. Use of a granular soil-applied systemic insecticide is discouraged because of toxicity concerns.
When an interior plant is heavily infested with mealybugs and your control efforts have not been successful, discarding the plant and purchasing an insect-free plant should be considered before the pests spread to other houseplants.
This article originally appeared in the 2/27/2004 issue.