Houseplant Pests - Identification and Treatment Methods

Plant insects aren't as big of a problem for indoor plants as they are for outdoor plants, but once an infestation does start it spreads easily, so care should be exercised to avoid it altogether.

If, despite your best efforts, you spot signs of plant insects, they should be dealt with swiftly in order to prevent them from spreading like a five-alarm fire.

In this article, I will discuss the five most common houseplant pests: aphids, white flies, spider mites, scale insects, and mealybug, and methods to control them.

In general, your best method of prevention is to carefully check your new purchases for plant insects before bringing them home. Once home, it is a good idea to keep your new houseplants isolated for a couple of weeks before placing them near the rest of your plants.

You also risk picking up houseplant pests on your indoor plants if you place them outside for fresh air. Instead, select a good interior location for your plants based on their light requirements, and they will thrive nicely without the risky outdoor trip.

If caught early enough, most houseplant pest infestations can be controlled by washing the plant with soapy water or swabbing them with alcohol. For this reason, you need to check your plants regularly, ideally when you do your weekly plant maintenance. Remember, houseplant pests spread easily, so don't use your feather duster on an infected houseplant!

Aphids are common houseplant pests from the lice family. They kill plants by sucking out the juices, causing stunted new growth and the foliage to turn pale and die. Aphids secrete a sticky substance called honeydew which promotes black mold. You will find aphids on the most vulnerable part of the plant---the underside of the leaves and on soft, new tip growth. Aphids are approximately 1/8" long and can be green, red, pink, yellow, brown or black in color.

A mild infestation of aphids can be controlled by picking off and crushing any visible aphids. After that, swab the leaves and stems with a soft cloth and soapy water (I use a mild dish soap) then rinse with clear, tepid water.

For serious infestations, take the plant to a well-ventilated area and spray with malathion. Wait for the chemical to dry completely, then rinse the foliage with clear, tepid water.

Plants that are susceptible to aphids are: Dieffenbachia, Ferns, Pittosporum, Fatshedera, and Ivies.

White Flies are small houseplant pests that fly off when you disturb the plant. White flies lay eggs on the undersides of the leaves which hatch into nearly transparent green larvae. The larvae actually do most of the damage to the plant by feeding on the sap, causing green leaves to turn yellow and drop off. White flies secrete a mold-causing, sticky substance called honeydew.

For whitefly control: Mild infestations require a strong spray of tepid water on the leaves, making sure to clean the underside of the leaves well.

For more serious infestations of white flies, you will need to move the plant to a well-ventilated area and spray with malathion. Spray from a distance of 18", let dry, then rinse the foliage with clear, tepid water.

Plants that are very susceptible to white flies are: Privet, Ferns, Begonias, and Coleus

Mealy Bugs are soft-bodied houseplant pests that approximate 1/4" in length and are coated in a white, powdery wax. There are two varieties of mealy bugs: the long-tailed variety bear live young, and the short-tailed variety lay approximately 600 eggs.

Mild mealybug infestations can be treated by dabbing the mealy bugs with a cotton ball dipped in rubbing alcohol. The mealy bugs will simply die and fall off. The alcohol treatment should be followed by washing the plant with warm, soapy water, followed by a rinse with clear, tepid water.

Plants that are severely infested with mealy bugs should be taken to a well-ventilated area and sprayed with a solution mix of 1/2 tsp. malathion and a few drops of liquid detergent to one quart water. After the solution dries, rinse the foliage with clear, tepid water.

Houseplants that are very susceptible to mealy bugs are: Coleus, Croton, Dracaena, Ferns, Palms, Cacti, and Cissus.

Spider Mites are red or green, microscopic houseplant pests that typically live under the leaves. Spider Mites spin fine white webs that cover the houseplant, causing the growth to become stunted and the plant to eventually die. The first signs of an infestation, though, is yellow or brown spots on the foliage. Cacti that are infested will become mottled and grey.

For new cases of spider mite infestation, spray small plants in the sink with a strong spray of tepid water. If the plant is too big for the sink, it may be wiped down with a soft, soapy cloth, then rinsed with clear, tepid water.

Serious infestations will require chemicals. Take the plant to a well-ventilated location and spray with malathion. You must wait for the chemical to completely dry, then rinse the foliage with clear tepid water. If the malathion doesn't work, then the plant should be destroyed.

Houseplants that are very susceptible to spider mites are False Aralia, Ivies, Schefflera, Cacti, and Asparagus Fern.

Scale insects look like little oval spots. They measure approximately 1/8" in length and are a yellowish brown or greenish brown in color. They live on the underside of the leaf along the main vain. Severe infestations will cause the plants to turn yellow and die. Scale insects are also secrete a sticky substance known as honeydew that causes mold.

For mild scale insect infestations, gently scrub the insects off of the leaves using a brush (it is amazing how stubborn these plant insects can be!) and warm, soapy water. Once you've cleared the plant, rinse it with clear, tepid water.

For severe scale insect infestations, take the plant to a well-ventilated area and spray with malathion according to package directions. Wait for the chemical to fully dry, then rinse the leaves with clear, tepid water.

Plants that are very susceptible to scale insects are Pittosporum, Aralia, Aloe, Croton, Dracaena, Ferns, Palms, Ivies, and India-Rubber Tree.