Common Houseplant Pests and How to Address Them
When a houseplant looks less than healthy, most often it is the result of improper care. Factors such as too much or too little water, light, heat or fertilizer can cause many plant problems. However, in some cases the problem results from a pest infestation. Several insects and other pests feed on houseplants. These pests most often come into the home on newly purchased plants or on those that have been outside for the summer.
Prevention
The best way to control insects and related pests on houseplants is through prevention, as it is almost always easier to prevent a pest infestation than to eliminate one. There are several precautions that you can take which will decrease the chances of having to deal with a pest infestation of your houseplants.
- Provide a plant with the growing conditions that it needs so that it is more likely to grow vigorously. Stressed plants tend to be more susceptible to pests.
- Before buying or bringing a plant indoors, always check it and its container for signs of pests.
- A plant that has been outside for the summer, especially one sitting on the ground, may have pests that have crawled in through the drainage holes. Take the plant out of the pot to examine the soil.
- Isolate new plants from plants already in the home for six weeks to ensure that any pest brought in will be less likely to spread.
- While plants are isolated, carefully examine them for signs of pests or damage on a regular basis of about once a week. Pay particular attention to the undersides of leaves where pests are most often found. Using a 10X magnifying lens will make it easier to see small pests and also immature pest stages. Infestations are often much easier to control if caught early.
- When repotting a plant, use commercially prepared potting soil rather than soil from outdoors, which can be a source of pests.
- Washing smooth-leaved plants every two to three weeks discourages pest infestations and also improves the appearance of foliage. Small plants can be inverted and swished in a bucket of tepid (lukewarm) water. To prevent loss of soil, cover it with aluminum foil or plastic wrap. Large plants can be hosed down gently, or upper and lower surfaces of leaves can be wiped with a soft, wet cloth. Large plants can also be rinsed in a tepid shower.
- Since cut flowers from the garden can be a source of pests, keep them separate from houseplants.
- Pests of houseplants can enter homes from outdoors, so make sure that screens and doors fit well.
Major Pests
Aphids
Aphids are small, soft-bodied, pear-shaped insects about 1/16th to 1/8th of an inch long. They are usually green but may be pink, brown, black or yellow. Some aphids have a woolly or powdery appearance because of a waxy coat. Adults may or may not have wings.
Aphids are usually found feeding on new growth or the undersides of leaves. Some feed on roots. They suck plant sap, resulting in yellowing and misshapen leaves. In addition, growth may be stunted, and new buds deformed. As aphids feed, they excrete a sugary material, called honeydew, which makes leaves shiny and sticky. Sooty mold fungi may grow on the honeydew, producing unsightly dark splotches on the plant’s surfaces.
How to Control Aphids
With minor infestations, handpicking, spraying with water or wiping the insects with a cotton swab dipped in rubbing alcohol may be practical. Insecticidal soap spray may also be used. In most cases the treatment will have to be repeated multiple times. For houseplants that are taken outdoors, spray with insecticidal soap, neem oil extract, pyrethrins, acetamiprid, imidacloprid, cyfluthrin, or permethrin to control aphids. See Table 1 for examples of brands and products. Imidacloprid plant spikes put into the soil will also control aphids. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.
Mealybugs
Mealybugs are small, pale insects, related to scales. They are about 1/8th to 1/4th inch long and move very sluggishly. The adult females cover themselves and their eggs with a white, waxy material, making them look cottony. Some have waxy filaments that extend beyond their bodies.
Nymphs (immature forms) hatch from the eggs. Once they begin to feed, the waxy coating starts to form. Nymphs look like adults only smaller. The wax on mealybugs helps repel pesticides and makes them somewhat difficult to control. Mealybugs are most commonly found on the lower surfaces of leaves and in leaf axils (where the leaf attaches to the stem). One species feeds on the roots. They suck plant sap, causing stunted and distorted growth and sometimes plant death. Like aphids, mealybugs excrete honeydew, providing the opportunity for growth of sooty mold fungi.
How to Control Mealy Bugs
Light infestations can be controlled by removing individual mealybugs by hand or by wiping each insect with a cotton swab dipped in rubbing alcohol. An insecticidal soap spray may also be used. With a heavy infestation, it may be necessary to discard the plant. For houseplants that are outdoors, spray with neem oil extract, pyrethrins, acetamiprid, imidacloprid, cyfluthrin or permethrin to control mealybugs. Imidacloprid plant spikes put into the soil will also control mealybugs. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.
Spider Mites
Mites are not insects but are more closely related to spiders. Since they are extremely small, plant damage is typically the first sign of their presence. A silky web is often seen with heavier infestations.
Both spider mite adults and their immature forms damage plants by sucking plant sap. Damage includes light-colored speckling on the upper surface of leaves, and results in a plant with an overall faded look. If the mites are left unchecked, leaves become bronzed or yellowed, and the plant dies. Spider mites are usually more of a problem on house plants that remain indoors year round.
How to Control Spider Mites
Spray sturdy plants forcefully with water, including the undersides of leaves, to dislodge mites and break up their webs. Plants also can be sprayed with an insecticidal soap. For houseplants that are outdoors, spray with insecticidal soap, neem oil extract or an insecticide containing sulfur. It is often necessary to spray once a week for several weeks to control mites. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.
Plants placed outdoors during summer may have a reduced problem with spider mites. Be sure to place all houseplants initially in mostly shade, as even plants that grow well in more sun might be burned until they have adapted to the higher light levels.
Fungus Gnats
Adult fungus gnats are delicate in appearance and about 1/8 inch long. Often they can be seen running across or flying near the soil surface under a houseplant. They are weak flyers and are attracted to light.
The adults do not feed on houseplants but can be a nuisance to people. In severe infestations they are often seen in large numbers on nearby windows.
The whitish larvae (immature forms) of fungus gnats have shiny black heads and can grow as large as 1/4 inch. The larvae generally feed on decaying organic material or fungi growing in the soil. The larvae of some species will also feed on roots. This feeding is especially damaging to very young plants. With older, established plants, the initial sign of an infestation is that the plant loses its normal healthy appearance. A heavily infested plant may lose leaves as a result of the feeding of larvae on its roots.
Indoors, fungus gnats are most often a problem when potting soil that is rich in organic matter, such as peat moss, is used to grow plants. It is especially a problem when overwatering occurs.
How to Control Fungus Gnats
For plants that can tolerate it (i.e. most houseplants, especially during winter), allow soil to dry between watering. Dry conditions will kill the larvae. Do not allow water to stand in the saucer beneath houseplant containers, and invert saucers beneath plants outside, so as to not collect rainwater. Products that contain strains of the biological control agent Bacillus thuringiensis subsp. israelensis can be applied to the soil of houseplants and watered into the soil for control. Follow label directions for safe use.
Root Ball Pests
Houseplants taken outdoors during the summer may have their root balls infested with pillbugs, millipedes and slugs. These houseplant pests may cause minor feeding damage to root systems. They are generally found along the exterior of the root ball in small cavities carved from the potting mix. Ants may also make nests within the potting soil of houseplants while outside.
How to Control Root Ball Pests
The plant container can be gently removed to inspect for pillbugs, millipedes and slugs, which simply can be scraped away. Ant colonies in the container may be killed by soil drenches of products containing cyfluthrin or permethrin. Mix insecticide at the same rate as for spraying, and pour solution through soil in container. Allow pots to thoroughly drain and dry before bringing indoors. Follow label directions for safe use.
Scales
Several species of scales are pests on houseplants. Scale insects can be divided into two groups: armored scales and soft scales. An armored scale secretes a waxy covering that is not an integral part of its body. The covering can be scraped off to locate the insect living beneath it. In contrast, the waxy covering that a soft scale secretes is an integral part of its body.
Scales are unusual insects in appearance. Adults are small and immobile with no visible legs. Scales vary in appearance depending on age, sex and species. Some are flat and appear like fish scales stuck to a plant. Others look like waxy, colored masses. They range in size from 1/16th to 1/2 inch in diameter. They are usually found on stems and the undersides of leaves, but may be found on upper surfaces as well. Scales feed by sucking plant sap.
Their immature forms, called crawlers, are mobile and also feed by sucking plant sap. Like mealybugs, the soft scale insects excrete honeydew (which results in black sooty mold problems on foliage and stems). Armored scales do not excrete honeydew.
How to Control Scales
Early infestations of scales can be removed by scraping with a fingernail. Adult scales are relatively protected from insecticides by their waxy covering. However, for houseplants outdoors, sprays with products containing neem oil extract or canola oil help control adult scale insects by smothering. Their crawlers are susceptible to many insecticides, such as insecticidal soap, neem oil extract, canola oil, pyrethrins, acetamiprid, imidacloprid, cyfluthrin or permethrin. Follow label directions for safe use.
Whiteflies
Whiteflies are not true flies, but are more closely related to scales, mealybugs and aphids. They are very small about 1/10th inch to 1/16th inch long. They have a powdery white appearance and resemble tiny moths. When at rest, the wings are held at an angle, roof-like over the body. The immature stage is scale-like and does not move.
Both the adults and their immature forms feed by sucking plant sap. The damage that they cause is similar to that caused by aphids. The infested plant may be stunted. Leaves turn yellow and die. Like aphids, whiteflies excrete honeydew, which makes leaves shiny and sticky and encourages the growth of sooty mold fungi. When plants that are infested with whiteflies are disturbed, the whiteflies flutter around for a while before settling again.
How to Control Whiteflies
Wash the plant. Spray the plant thoroughly with insecticidal soap, especially the lower leaf surfaces. Imidacloprid plant spikes put into the soil will also control whiteflies. For houseplants that are taken outdoors, spray with insecticidal soap, neem oil extract, acetamiprid, imidacloprid, cyfluthrin or permethrin to control whiteflies. See Table 1 for examples of brands and products. Follow label directions for safe use.
Natural, Less Toxic Insecticides
| Insecticide/Miticide Active Ingredient | Pests Controlled | Examples of Brands & Products | ||
| Bacillus thuringiensis subsp. israelensis H-14 | Fungus gnat larvae in potting soil | Gardens Alive Knock-out Gnats Granules | ||
| Insecticidal Soap | Aphids, spider mites, mealybugs, scale crawlers, whiteflies | Bonide Insecticidal Soap RTU Garden Safe Insecticidal Soap Insect Killer RTU Safer Brand Insect Killing Soap RTU Espoma Earth-tone Insecticidal Soap RTU |
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| Sulfur & Pyrethrins | Spider mites, scale crawlers | Espoma Earth-tone 3-in-1 Disease Control RTU Bonide Eight Insect Control Home & Garden RTU Whitney Farms 3-in-1 Rose & Flower Care |
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| Neem Oil Extract | Aphids, spider mites, mealybugs, scale (adults & crawlers), whiteflies | Natural Guard Neem RTU Garden Safe Fungicide 3 RTU Monterey Neem Oil RTU Safer Brand Neem Oil RTU Bonide Neem Oil RTU |
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| Canola Oil & Pyrethrins | Aphids, spider mites, mealybugs, scale (adults & crawlers), whiteflies | Espoma Insect Control RTU Monterey Take Down Garden Spray RTU |
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| Cottonseed Oil, Clove Oil, & Garlic Oil | Mites, Thrips, Aphids | Bonide Mite-X RTU | ||
| Rosemary Oil, Clove Oil, & Cottonseed Oil | Mites, whiteflies, aphids, scale crawlers, mealybugs, | Monterey All Natural Mite & Insect Control RTU | ||
| Spinosad | Thrips, caterpillars, leafminers | Bonide Captain Jack’s Dead Bug Brew RTU | ||
| Spinosad & Insecticidal Soap | Aphids, leafminers, mealybugs, spider mites, thrips, whiteflies, scale crawlers | Natural Guard Spinosad Soap RTU | ||
| Pyrethrins | Aphids, whiteflies | Bonide Japanese Beetle Killer RTU Garden Safe House Plant & Garden Insect Killer RTU |
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| Pyrethrin and Neem oil | Aphids, mites, whiteflies | Ferti-Lome Triple Action Plus RTU | ||
| Hot Pepper Wax | Aphids, mealybugs | Hot Pepper Wax Insect Repellent RTU | ||
| Rubbing Alcohol | Mealybugs, aphids, whiteflies, scale crawlers | Multiple brands (applied with cotton swabs, such as Q-Tips) | ||