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.
Houseplants are susceptible to attack by many insects and mite pests. Some of these houseplant pests can cause extensive damage to the appearance and health of the plant while others are simply a nuisance.
Plants that are not vigorously growing and/or are under stress may be particularly susceptible to insect and mite injuries.
Infestations of scale insects (mealybugs and whiteflies) are almost always established from infested plants recently purchased or received as gifts.
As a precaution, all new plants should not be placed with existing houseplants for at least three weeks.
A careful inspection at the end of this time helps determine the presence or absence of pests.
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Houseplant Pest 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.
Methods Used to Control Houseplant Pests
Many household plant pests can be controlled, at least in part, by washing the plant periodically with a vigorous jet of water. This is particularly effective for spider mites and aphids, which are most readily dislodged.
Watering affects houseplant pests in a couple of different ways. Excessively moist soil favors the development of problems with fungus gnats. However, plants placed in very hot, dry sites are prone to problems with spider mites.
Larger houseplant insects can be controlled by handpicking. This is especially useful for scale insects and mealybugs. Regularly using small, hand-held vacuums assist in controlling whiteflies.
Yellow sticky traps can be useful to reduce the number of insect pests that fly – whiteflies, winged aphids, and fungus gnats. These traps are sold commercially or you can easily make them by cutting bright yellow cardboard and covering it with petroleum jelly or some other sticky material. However, trapping alone will not entirely eliminate problems because much of the population, including the younger stages, remain on or about the plants.
Seriously infested plants are often best discarded because they usually require lengthy and extraordinary efforts to control the pests. They may also serve as a source for infesting other plants. You can use periodic “host-free” intervals to cause insects that survive for short periods without feeding to die out.
Under certain conditions, natural enemies of houseplant pests are effective in reducing the problem to acceptable levels. However, they are relatively difficult to acquire and are usually available only through specialty suppliers.
Sprays of alcohol, or alcohol dabbed onto insects, is well known as a useful control of mealybugs. However, using alcohol on plants may cause injuries such as leaf burn. Carefully test a small part of the plant if you attempt to use this method.
Insecticidal soaps (potassium salts of fatty acids) are one of the most commonly available houseplant insecticides. These are used as dilute sprays (one to three percent concentration) and can help control many houseplant insects and spider mites. Many liquid hand soaps and dishwashing detergents also have insecticidal effects, although there is potential for plant injury with such treatments.
Diluted sprays of oils (petroleum distillates, mineral oils) are some of the most useful insecticides for houseplant pests, capable of controlling scales, young whiteflies and spider mites. These are highly refined oils that primarily act by smothering.
Some houseplant insecticides are derived from seed extracts of the neem plant, a commonly grown tree in many tropical areas. Neem seed contains materials that disrupt insect growth and is useful for control on developing whiteflies and some other insects. Neem seed also contains oils that may be used in a manner similar to other horticultural oils and is sold in products labelled as containing “clarified hydrophobic extracts of neem seed.
Non-Chemical Control of Houseplant Pests
The first step in control is to isolate any plant suspected of being infested with a pest.
Keep the plant separate from other houseplants until the pest is completely controlled.
This process may take several weeks or more.
Before looking for a chemical solution to a pest problem on houseplants, there are several effective control alternatives that should be considered. However, do not expect the problem to be solved with one application. Some of these alternatives require persistence on the part of the indoor gardener, but they can give good control.
If only an isolated portion of the plant is infested, as occurs with leafminers, remove and destroy the infested parts.
- If the roots are infested, take a cutting and start a new plant.
- Be sure to start with a clean pot and sterile potting soil.
- Early infestations can often be removed by handpicking.
- Use a cotton swab dipped in rubbing alcohol to wipe off insects such as aphids and mealybugs. Scale insects may need to be scraped off with a fingernail.
- Spraying a sturdy plant with water will remove many pests. Be sure to spray all plant surfaces. Repeated water sprays help control spider mites.
- Spraying the plant with an insecticidal soap can often eliminate a pest infestation in its early stages.
- Insecticidal soaps are contact insecticides and are only effective when they make direct contact with insects.
- Once the soap solution dries, it has no effect against pests. Insecticidal soaps are most effective against soft bodied insects and related pests, such as aphids, mealybugs, immature scales (crawlers), thrips, whiteflies and spider mites.
- Since pests may be hidden or in the egg stage, it often takes more than one treatment to eliminate them.
- If the plant is severely damaged and is not a valuable one, the best and simplest solution may be to discard the plant and its soil and start with a new plant.
If non-chemical control methods have failed, and the plant is valuable, a stronger pesticide may be necessary.
Before choosing a pesticide, it is important to identify the pest accurately.
In general, a single pesticide will not kill all kinds of pests.
Some pesticides are only effective against certain pests or certain life stages of particular pests.
In addition, it is important to understand that more than one application of a pesticide is often necessary for control. When possible, alternate the pesticide used from one application to the next as some pests develop resistance quickly.
Houseplant insect sprays can be obtained at garden centers and farm supply stores. Only a few pesticides are labeled for use indoors on houseplants.
Before using a pesticide indoors, be sure that the label specifies that use.
You may want to treat your plant outdoors and then bring it inside after the pesticide has dried completely.
If you take plants outdoors to treat, make sure that weather conditions are mild.
Spraying insecticides outdoors prevents over-spray from contacting furniture, drapes or carpet.
Typically, a pesticide label will include both a list of plants for which the pesticide is recommended as well as a list of plants that are known to be sensitive to the pesticide.
Symptoms of pesticide injury on plants include distortion of leaves and buds, yellowing of leaves, spotting of leaves or flowers, and burn along the leaf edges as well as total burn.
When damage occurs, it often becomes visible within 5 to 10 days, sometimes sooner. In general, the damage does not kill the plant.
As always, before purchasing and using any pesticide, be sure to read all label directions and precautions, and then follow them carefully.
Major Pests That Love Houseplants
Aphids come in many varieties and can be just about any color. They are small and fat and juicy – and gross.
What Are Aphids?
Aphids are small, soft-bodied, pear-shaped insects about 1/16– to ⅛-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.
Aphids can also have wings, but winged aphids are less common. Like most indoor plant pests, aphids feed on a houseplant by sucking the sap from the leaves.
They like to cluster and feed on the new growth and flower buds of a plant, which causes stunted growth and deformed leaves and flowers.
Thankfully, aphids don’t cause catastrophic damage to a houseplant, and infestations aren’t usually fatal.
Aphids multiply quickly, the life cycle of an aphid is about one week.
You may notice a bunch of tiny white flecks on the leaves and around the base of the houseplant several days before seeing the adults – those are the eggs.
Every time I’ve seen white fleck on a houseplant, sure enough a few days later adult aphids would appear.
How To Control Aphids on Houseplants
Aphids can become immune to pesticides so it’s best to use natural methods to kill these pests. If you discover aphids on a plant, act fast because aphids can spread like wildfire to your surrounding houseplants.
- Spray the leaves of the infested houseplant with a strong stream of water to rinse off all of the aphids that you see. You can do this task in the sink, or in the shower for larger houseplants. Then wash the leaves with a weak solution of mild liquid soap (I use Dr. Bronner’s Baby-mild Liquid Soap) and water.
- If the houseplant is too large to move, mix a small amount of mild liquid soap in a spray bottle full of water and use this to wash the leaves (I use 1 tsp Dr. Bronner’s Baby-mild Liquid Soap per 1 liter of water). Before spraying or washing any houseplant with soapy water, be sure to test it on oneleaf to make sure it won’t damage the plant.
- Neem oil is also very effective to control aphid infestations, and has a residual effect to keep them from coming back quickly. You can buy neem oil for pretty cheap, and a big bottle will last a long time. It works wonders for eliminating an aphid infestation.
- You could also use rubbing alcohol to kill aphids by using a cotton swab to dab the rubbing pests.
- As with mealybugs, if you have ants, they may be causing the problem! Ants will bring aphids toa houseplant so that they can feed off of the honeydew which is produced when aphids feed on the plant. I know this sounds crazy, but it’s a fact. So make sure that you watch out for ants.
Where do aphids come from?
If you have aphids on your indoor plants, they probably came in on a plant that spent the summer outside.
Aphids could also come from flowers or produce that has been brought in from the garden, or from the grocery store.
Mealybugs are clever little devilsthey like to hide and then come in for the sneak attack. Your Houseplants look fine one day and it seems like overnight the stems are covered with white fluffy stuff. Dreaded mealybugs are tough opponents, but we can be smarter, and ultimately win the battle.
What are Mealybugs?
Mealybugs are scale insects that suck the sap out of the leaves and stems of plants; resulting in stunted or deformed leaf growth, yellowing of the leaves, and leaf drop.
The damage caused by mealybugs is not as quick to occur or as devastating as it is with spider mites.
If a mealybug infestation goes left untreated, the plant will eventually die; although it will usually take a long time for mealybugs to kill a plant.
Mealybugs can be found anywhere on a plant, but are most commonly found on new growth, along the veins of leaves, and at the leaf joints.
They are white and most commonly look like cotton around the base of the leaves or stems of the plant.
Mealybugs can also appear brown or cream colored, and waxy in immature stages. They are commonly mistaken for disease or mildew rather than bugs.
It takes a week or two for mealybug eggs to hatch.
Most of the time mealybugs don’t appear to move, but in their early stages mealybugs can crawl around on a plant and move to other houseplants in the area.
The worst part is that mealybugs will leave the houseplant to hide, and can live for a long time in spaces and crevices without having a host plant.
So just when you think you have conquered the beast, they will come out of hiding and re-infest your houseplant when you’re not looking. Gross!
How To Kill Mealybugs On Houseplants
As with any houseplant pest infestation, when you first spot a mealy bug problem begin treatment immediately.
I don’t recommend using synthetic pesticides, because mealybugs are resistant to most pesticides.
They also have the ability to develop a resistance to any pesticides they are exposed to on a regular basis.
- One way to kill mealybugs on houseplants is by touching them with a cotton swab that’s been soaked in rubbing alcohol. In order for rubbing alcohol to be effective, it must come in direct contact with the mealybugs.
- As you treat a houseplant, make sure to inspect underneath all leaves, around the leaf joints, in folds and at the base of the plant for mealybugs. They like to hide so check the plant from several angles and under each leaf. Also brush away a little dirt and check the base of the stem at the point where it sticks out of the dirt, you may find some mealybugs hiding there.
- Use a solution of soapy water and spray it on the leaves of your infested plant (I use 1 tsp of Dr.Bronner’s Baby-mild Liquid Soap per 1 liter of water). If the plant is small enough, bring it to the sink or shower and wash the leaves with this soap and water solution. Keep in mind that soap can damage the plant, so it’s best to test it on a few leaves before spraying the entire plant.
- Neem oil is very effective to control mealybug infestations, and has a residual effect to keep them from coming back quickly. You can buy neem oil for pretty cheap, and a big bottle will last a long time.
- Mealybugs can live in the soil of a houseplant so if a plant is plagued by recurring infestations, you could try removing the top inch of dirt from the pot and replacing it with fresh potting soil.
- Remove the plant from the area and clean any crevices where mealybugs could be hiding. Besure check around the outside lip and inside edges of the pot and tray, and also the bottom of the pot for hiding mealybugs.
- If you have ants, they may be causing the problem! Ants will bring mealybugs to a houseplant so that they can feed off of the honeydew residue that’s produced by mealybugs. I know this sounds crazy, but it’s a fact. So make sure that you watch out for ants.
It’s hard to get rid of all the mealybugs the first few times you try.
Even if you are able to kill all of the adults, the eggs and babies are tiny and easily overlooked.
It can be frustrating, but it’s worth it to save your favorite houseplants.
Mites are not insects but are more closely related to spiders. Spider mites are sneaky little suckers.
Since they are extremely small, plant damage is typically the first sign of their presence. A silky web is often seen with heavier infestations.
They are difficult to see, and usually by the time you notice them on a houseplant, it’s already been heavily damaged.
You might notice spider webbing on a houseplant, or the plant may look dirty.
From a distance, the houseplant might look like it isn’t getting enough water… but take a closer look, hold the plant up to the light and look under the leaves.
You should be able to see the tiny little mites moving around on fine webbing. Gross!
What are spider mites?
Spider mites are not technically insects, therefore cannot be controlled with insecticides, systemic or other.
Spider mites thrive in warm, dry conditions – and during the winter, your the house becomes the perfect breeding ground.
They tend to start their webs on the underside of leaves and at the leaf joints.
Spider mites multiply very quickly and, in the right conditions, can double their population every couple of weeks.
Spider mites become fully grown about a week after they hatch.
It only takes a few weeks for an adult female spider mites to lay hundreds of eggs, and for those eggs to hatch, resulting in exponential population growth.
Spider Mite Damage On Houseplants
In my experience, spider mites are one of the most destructive houseplant pests.
They can devastate or even kill a houseplant in a very short period of time.
Spider mites suck the sap out of the leaves making them look discolored, speckled, curled under, dried or shriveled up.
The infested leaves will die and start to fall off, which will ultimately kill the houseplant.
How To Control Spider Mites On Houseplants
There are pesticides that are specifically designed for mites, but spider mites may develop resistance to them in a short time so I don’t recommend them (plus synthetic pesticides are toxic to humans and pets too, so I don’t recommend using them anyway).
- Use a solution of soapy water and spray it on the leaves of the infested houseplant (I use 1 tsp of Dr. Bronner’s Baby-mild Liquid Soap per 1 liter of water). If the plant is small enough, bring it to the sink or shower and wash the leaves with this soap and water solution. Keep in mind that soap can damage the plant, so it’s best to test it on a few leaves before spraying the entire plant.
- Neem oil is very effective to control spider mite infestations, and has a residual effect to keep them from coming back quickly. You can buy neem oil for pretty cheap, and a big bottle will last a long time.
- Be sure to focus your spray on the undersides of the leaves, this is where spider mites lay their eggs.
- Since spider mites thrive in dry conditions, keeping the air around your plants humid will help prevent infestation. Misting houseplants regularly helps to prevent spider mites. You could also try leaving a container of water near your plants.
- Make sure to keep your houseplants healthy, and maintain adequate soil moisture. A soil moisture gauge is a great healthy houseplants will allow them to protect themselves against spider mite infestations.
- Trim heavily infested leaves from the plant and throw them in the garbage (but don’t remove all the leaves from a houseplant).
- The best way to avoid heavy spider mite damage to your houseplants is to start treating the plant as soon as you discover the pests. As with any houseplant pest problem, make sure you check your houseplants on a regular basis for any signs of problems.
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.
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.
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 ¼-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.
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 controlagent Bacillusthuringiensis subsp. israelensis can be applied to the soil of houseplants and watered into the soil for control.
Less Common Houseplant Pests
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.
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.
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 1/16 to ½-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.
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.
Whiteflies are not true flies, but are more closely related to scales, mealybugs and aphids. They are very small about 1/10 to 1/16 -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.
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.
Thrips are tiny, slender, yellowish to blackish insects with fringed wings. They are typically found on leaves and between flower petals. At less than 1/16 inch in length, the adults are very difficult to see without a magnifying lens.
Blowing lightly into blooms and leaves causes thrips to move around quickly, making them easier to see.
Both adults and nymphs (immature stage) feed by scraping surface cells to suck plant sap. Leaves fed on by thrips will often take on a silvery or speckled appearance similar to damage caused by mites.
Leaves may drop early. When thrips feed on flower buds, the flower may die without opening. Flowers may be streaked or distorted as a result of feeding.
Rinse leaves with water. Spray plants with an insecticidal soap. For houseplants that are outdoors, spray foliage with spinosad, acetamiprid, imidacloprid, cyfluthrin or permethrin to control thrips.
For plants with flower buds infested with thrips, the insecticide must have systemic activity, such as spinosad, acetamiprid or imidacloprid, in order to control the hidden thrips.
Springtails are tiny insects about 1/5- inch long that inhabit the soil. They vary in color but are usually white or black. They are wingless, but can jump. Their presence is usually a sign of overwatering.
While springtails normally feed on decaying organic matter, they will chew on seedlings or tender plant parts. Damage is usually minimal. In large numbers, they can be a nuisance.
For plants that can tolerate it (most plants), let the soil dry between watering.
Leafminers are the larvae (immature worm-like stage) of a large number of different insects. The larvae feed between the upper and lower leaf surfaces.
Leafminer damage appears as a winding, discolored trail or an irregular blotch within the leaf. Although damage from these pests is unsightly, it is rarely serious.
Remove and destroy any leaves showing leafminer damage. For houseplants that are outdoors, insecticidal sprays that have foliar systemic activity (the ability to move into the leaves), such as acetamiprid, imidacloprid, or spinosad will control leafminers. Imidacloprid plant spikes put into the soil are also effective.
Various kinds of beetles and their larvae feed on houseplants. They may enter the home when houseplants are brought inside at the end of summer, or they may enter through some opening. They have chewing mouthparts.
Remove and destroy the beetles. If houseplants are outside and beetles return and feed on foliage, spray with neem oil extract, acetamiprid, imidacloprid, cyfluthrin or permethrin to control them for one to two weeks.
Caterpillars are the larvae of butterflies and moths. They range in size from about ⅛ inch to 2 or more inches long. Their color varies according to species with gray, brown, and green being common, as are mottled and striped colors. They may be smooth or have spines, hairs or bumps along their bodies.
Butterflies and moths lay their eggs on the undersides of leaves of plants that have been outdoors. Stray moths that have gotten into the home can also lay eggs on houseplants. When the eggs hatch, the caterpillars can be quite small, but grow with each molt (process of shedding the skin).
Caterpillars have chewing mouthparts. Some feed openly on leaves, buds and flowers and can eat large portions of the plant in a relatively short period of time. Others bore into stems to feed.
A good indication that caterpillars are causing the damage is the presence of frass (fecal pellets) on leaves and under the plant.
Remove and destroy caterpillars and eggs. If the houseplants are outside and additional caterpillar feeding occurs, spray with neem oil extract, spinosad, cyfluthrin or permethrin to control them for one to two weeks.