Prevent mealybug pests from preying on houseplants
Houseplants thrive when they are grown in conditions that meet their lighting, humidity, temperature and moisture needs. When houseplants are deprived of their preferred environmental conditions, they become susceptible to diseases and pests.
During the winter months, one pest in particular attacks and kills plants if left unchecked — mealybugs.
Mealybugs are members of the Pseudococcidae family of insects. These wingless insects appear on plants as waxy, cottony white clumps and are approximately 1/16 to 3/16 inches long. There are many species of mealybugs, which makes all houseplants susceptible to them.
The citrus mealybug (Planococcus citri), the most common species found on plant foliage, prefers soft-stemmed and succulent plants such as coleus (Plectranthus spp., fuchsia (Fuchsia spp.), croton (Codiaeum spp.), jade plant (Crassula ovata), poinsettia (Euphorbia pulcherrima), gardenia (Gardenia jasminoides) and many types of cacti. This species also feeds upon rosemary (Salvia rosmarinus), citrus, and bird of paradise (Strelitzia reginae). The most obvious signs of infestation are stunted or distorted leaves.
The ground mealybug (Rhizoecus falcifer) is the most common soil mealybug. This insect affects the roots of many houseplants, especially African violets (Saintpaulia spp.). Feeding on the plants’ root hairs results in yellowed leaves, wilting, stunting, and bloom reduction.
Mealybugs are attracted to wet soil and high nitrogen levels, found in overwatered and over-fertilized houseplants. Once established, mealybugs feed on plant sap and leave large amounts of excrement (honeydew). These make the plant sticky and provide a medium for a sooty mold growth, which can inhibit photosynthesis.
The home environment can also precipitate the appearance of mealybugs. Tender plants grown in wet, undrained soil in rooms with poor air circulation and warm ambient temperatures are very susceptible to mealybugs.
Read the plant label before purchasing to ensure that your home environment is suited to the plant you are considering for purchase. When purchasing house plants, be mindful that purchased plants may have undetected mealybugs, and when brought into your home, these mealybugs can quickly spread to existing plants.
There are numerous methods to prevent and treat mealybug outbreaks.
Environmental factors that prevent or ameliorate mealybug outbreaks include maintaining cool ambient temperatures at night, allowing the soil to dry out in between waterings, establishing a watering schedule, and providing adequate lighting.
Routinely inspect houseplants for signs of mealybugs. Look for mealybugs on the underside of leaves, on stems, in new leaf folds and on the tips of new foliage.
As soon as mealybugs are detected, treat the plant immediately. Remove and isolate the plant. When a few insects are present, hand pick them or wipe them off carefully.
For a minor infestation, manually remove the offending insects using cotton swabs and 70% or less isopropyl (rubbing) alcohol solution. Dab a cotton swab in rubbing alcohol and wipe the mealybugs away from the leaves and stems. Observe the plant for one to two days to make sure the alcohol did not harm the leaves.
For a severe infestation, you can prune the stem or remove the leaves. Immediately dispose of the infected foliage, as these pests will live as long as the foliage has moisture. Afterwards, clean pruning tools, discard the cotton swabs, and wash your gloves and hands. Note any presence of honeydew on the leaves as well as the plant container, saucer, and nearby areas. Clean these surfaces with a disinfecting solution.
Look for mealybugs and honeydew on nearby plants, as well as sticky surfaces. Ants can be attracted to the honeydew, and thorough cleaning of surfaces should discourage their appearance.
If the mealybugs persist after treatment with rubbing alcohol, consider using horticultural oil or insecticidal soap. Follow the label directions and treat the plant in a well-ventilated area away from other plants and pets. Alternatively, discard the infected plant and purchase a new healthy one.
Penn State Extension has information about mealybugs, pests and diseases affecting houseplants at extension.psu.edu.
Because mealybugs can be difficult to treat and eradicate, indoor environmental stewardship is the key to healthy plants. Keep houseplants in proper lighting, with adequate water, temperature, air circulation, and humidity. Houseplants are dormant in the winter, therefore fertilizing during that time is unnecessary.
For questions about houseplants and mealybugs, call the Garden Hotline of the Penn State Extension Master Gardeners of Butler County at 724-287-4761, ext. 7, or email the Master Gardeners at butlermg@psu.edu.
Mary Shannon and Lisa Bernardo are with the Penn State Extension Master Gardeners of Butler County.
