Houseplant bugs usually enter your home as unwanted stowaways on newly purchased plants. Once in your home, they can quickly spread to other houseplants, where they damage plants by actively feeding on the leaves or sucking the juices from plants. Insect pests on outdoor plants are often controlled by natural predators, such as snakes, frogs, birds and beneficial insects. Seasonal weather changes also help control insects outdoors. In your house, however, you are the only protection from insect infestations. Once introduced into your home, houseplant bugs are often difficult to eradicate. Many pests carry or spread disease, as well. Careful purchase and initial care will help reduce insect problems.
Some plants seem to attract more pests than others. Plants, such as cyclamen or African violet, that have fragrant blooms or tender vegetation are usually more attractive to pests than hardy plants with woody stems, such as corn plants. Choose plants that require little maintenance to remain healthy and you’ll likely reduce problems with disease and insect pests.
Identification of Houseplant Bugs
Most houseplant bugs are small and hard to see. Whiteflies are a common problem in greenhouse culture and, as their name implies, are small, white flies that dwell on the undersides of leaves. Spider mites are small, spider-like insects that may be red, brown, gray, black or spotted. You might confuse mealybugs with a plant disease. These unusual insects rarely move, but sit on the plants, resembling tiny spots of white cotton.
Aphids are usually wingless insects, less than ¼ inch long, and gray, green, red or brown. They also live on the undersides of leaves. Thrips are very tiny and you probably will notice the damage they cause before you see them. Scales are brown, white or cream insects that form in colonies on plants. When massed close together, they may not look like insects at all, but an infectious growth on the plant.
Damage from Houseplant Bugs
Almost all houseplant pests suck the juices of the plants through piercing mouth parts. Feeding results in yellowed, wilting or limp leaves and stems. You may also notice honeydew, a sticky substance secreted by aphids and whiteflies on the leaves. Honeydew, in turn, attracts sooty mold, an unattractive black growth that feeds on the honeydew. Thrips and spider mites tunnel through the leaves, leaving small, white stipled areas on the leaves. You may also notice transparent spots or webbing on the undersides of the leaves.
Preventing Bugs in your Houseplants
Buy houseplants at a reputable nursery and examine plants closely for signs of insect infestation. Look under the leaves and avoid plants with ragged, yellow or drooping leaves, which are signs of insect infestation or disease.
When you first bring a plant home, wash its leaves in a gentle stream of water to dislodge any stowaways. Quarantine the plant in a room away from other houseplants for two to three weeks to ensure that it has no pest or disease problems. Check it daily, looking under the leaves and on the stems of the plant. Another option is to place a plastic bag over the plant for a few days to capture any escaping pests.
If you move plants outdoors during the summer, follow the same procedures when moving them indoors in the fall.
Keep houseplants healthy by providing proper growing conditions. Most houseplants need moderately moist soil and bright light. Healthy houseplants are better able to fend off insect infestations. Clean up any dead leaves and plant debris and wash the plants from time to time to remove dust. Avoid over fertilizing houseplants, which encourages rapid new growth and makes them more vulnerable to damage from insects and disease.
Control of Houseplant Bugs
The least invasive control for houseplant insects is a stream of water. Cover the base of the plant with your hand to keep the soil in the pot and turn the plant upside down. Wash it gently over a sink to dislodge any pests.
Spray the plant with insecticidal soap or oil to control most houseplant insects. Insecticidal soaps and oils work by coating the soft bodies of these pests, smothering them and drying them out. Coat the leaves thoroughly, both tops and bottoms with the product every week. Dab aphids and mealybugs with rubbing alcohol on a cotton ball.
Pesticides, such as pyrethrum or neem oil, effectively control houseplant insects, but follow package directions carefully and take the plant outside to apply the pesticide. Avoid the use of pesticides on houseplants, if possible, to reduce your exposure to these chemicals. Often, the best course is to discard a severely infested houseplant, since treatment is difficult and the insects will likely infest other plants, as well.
For Further Reading on Identifying and Managing Houseplant Insects and Pests