Diagnosing Houseplant Problems from Insect Pests

Growing indoors plants is a rewarding hobby that yields beautiful results.  But when problems arise with your indoor plants, it can be difficult to determine what to do to fix the problem.  

When you encounter a houseplant problem, first ask yourself, Are the environmental conditions appropriate for this species?

If problems arise, start by understanding the needs of that particular species for light, soil, water, humidity, temperature, and fertilizer.  If these environmental conditions are not ideal, they must be changed or the houseplant must be moved to a location where they are ideal.

Many problems are not caused by a single factor – they are the result of several factors coming together to cause an unhealthy or unattractive plant.  Always look for more than one factor that could be contributing to the issue and correct all of them to solve the problem.  It is also important to identify the primary issue.  Some problems are caused by other factors and while you can address the problem, if you don't solve the primary issue the problem will always return.

Insects & Other Pests of Houseplants

While a wide range of species are grown as houseplants, there are only a few ubiquitous pests that impact indoor plants.  Insects and other pests are often difficult problems on houseplants. When left unmanaged, they can quickly cause extensive damage to plants. 

Monitor for pests frequently and deal with them as soon as they are noticed while populations are small.  When managing any houseplant pest, often the best results come when you pair multiple techniques simultaneously.  For example, rather than just spraying an insecticidal soap to control aphids, pair it with a good rinse and selective pruning to get good results. 

Mealybug  |  Scale  |  Fungus Gnats  |  Spider Mites  |  Aphids  |  Whiteflies  |  More Information  |  Back to Main Page

Mealybug

Mealybugs are white, cottony insects often found clustered in leaf axils and the undersides of leaves.  They emerge from egg masses and crawl around the plant to find a place to pierce the plant and suck sap. Once they start feeding on the plant, they remain stationary the rest of their life. They produce honeydew which makes lower leaves, tables, and floors sticky and over time the sticky deposits turn black with sooty mold.  Plants are weakened from the feeding causing stunted growth, yellow and deformed leaves, and when infestations are big enough, death.

Management:

• Mealybug is very difficult to control as they easily hide and their waxy coating makes them difficult to control with insecticides.
• Scout often and catch it early.  Deal with it right away to prevent populations from becoming unmanageable.
• Mealybugs produce honeydew which causes leaves and areas around the houseplant to have shiny clear spots.
• If only a few are found, spot treat with a spray of rubbing alcohol or a cotton swab dipped in rubbing alcohol. 
• Insecticidal soap, neem, and pyrethrin are all relatively safe insecticides that can be used indoors to treat this pest.  Apply frequently as insecticides are most effective on the immature “crawlers” which hatch every few weeks.
• Granular insecticides applied to the soil can also be used but may not be a good choice for homes with pets or children who may dig in the soil because of their toxicity.  Be sure the plant species being treated is on the label and always follow the label directions.
• While the use of biological control is not practical at home, it can be considered for greenhouses and botanical gardens.
• In many cases it is better to destroy heavily infested plants before they infest nearby plants.  

Click here for pictures, video and more information on mealybugs.

Scale

Scale looks like small bumps or scales clustered or lined up along stems and leaf veins, typically on the underside.  These sucking insects hatch from eggs held under the hard protective covering of their mother, crawl around the plant, and then pierce the plant to suck sap.  They remain stationary for the rest of their life.  Scale insects produce honeydew which makes lower leaves, tables, and floors sticky and over time the sticky deposits turn black with sooty mold.  Plants are weakened from the feeding causing stunted growth, yellow and deformed leaves, and when infestations are big enough, death.

Management:

• Scale is very difficult to control as the protective covering makes them difficult to control with insecticides.
• Scout often and catch them early.  Deal with infestations right away to prevent populations from becoming unmanageable.
• For light infestations, remove individual insects with your fingernail.
• If only a few are found, spot treat with a spray of rubbing alcohol or a cotton swab dipped in rubbing alcohol. 
• Prune out branches or leaves that are heavily infested.
• Insecticidal soaps, pyrethrin, rotenone, resmethrin, and acephate are insecticides that can be used indoors to treat for scale.  Apply weekly for at least 4 to 6 weeks as insecticides are most effective on the immature “nymphs”  that hatch on a rotating basis.
• Granular insecticides to soil can also be used but may not be a good choice for homes with pets or children who may dig in the soil because of their toxicity.  Be sure the plant species being treated is on the label and always follow the label directions.
• In many cases, it is better to destroy heavily infested plants before the scale can infest nearby plants.

Fungus Gnats

These small, black, flying insects are very mobile and do not cause notable damage to houseplants but are a big nuisance.  The larva thrive in wet soils and feed on decaying organic matter, including root systems that have died from overwatering but cause very little damage to plants.  Because fungus gnats prefer moist soils, they are good indicators of over-watering.

Management:

• Allow the soil, especially the soil surface, to dry out between waterings.
• Never allow plants to sit in saucers or outer pots filled with water.
• Insecticides are not needed when soils are allowed to dry out.
• Other recommendations of covering the soil surface with sand or rocks are not necessary – just let the soil dry between waterings.  It's good for your houseplants to do that anyway!
• Yellow sticky card traps can catch flying adults, but do not prevent new insects for hatching.
• Fungus gnats do not always originate from plants.  Check unused drains, condensation trays or other wet areas.

Spider Mites

These arachnids (not insects) are closely related to spiders and ticks.  They are very small and difficult to see and live primarily on the undersides of leaves.  Often the best way to find them is to tap leaves over a piece of paper and look for tiny specks that move around on the paper.  Spider mites prefer dry conditions and when populations are big enough, will produce fine webbing on leaves and stems. While they feed on nearly any houseplant, some species like Norfolk island pine, ivy, and croton, are highly susceptible.  Mites feed by piercing and sucking leaves causing a mottled appearance.  As infestations get worse the yellow-green mottling turns to tan and eventually leaves fall off.

Management:

• Scout often and catch spider mites early.  Deal with this pest right away to prevent populations from becoming unmanageable.
• Since they prefer dry conditions, raising the humidity can slow population growth.
• Rinse foliage thoroughly in a shower or outdoors.
• Remove branches or leaves that are heavily infested.
• A miticide or other pesticides like insecticidal soap or horticultural oil can be applied according to label directions.  Be sure to thoroughly treat the underside of the leaves.  Multiple applications on weekly basis for 4 to 6 weeks will be needed for complete control.
• In many cases it is better to destroy heavily infested plants before they infest nearby plants. 

Aphids

These small, soft-bodied insects are often green, brown, or reddish in color.  They typically cluster on growing points, underneath leaves, along stems, and on flower buds.  They have sucking mouthparts and produce honeydew which makes lower leaves, tables, and floors sticky and over time the sticky deposits turn black with sooty mold.  Plants are weakened from the feeding causing curled, yellow, and deformed leaves that eventually drop off.  When infestations are big enough, plants can die.

Management:

• Scout often and catch it early.  Aphid populations can grow quickly.  Deal with them right away to prevent populations from becoming unmanageable.
• For light infestations, a forceful spray of water can dislodge most aphids. 
• Remove branches or leaves that are heavily infested.
• Insecticidal soap and other insecticides labeled for use on indoor plants are options for treatment.  Always follow label directions.
• In many cases it is better to destroy heavily infested plants before they infest nearby plants. 

Whiteflies

Whiteflies are small white, flying insects that are highly mobile making them difficult to control.  They land and feed on the undersides of leaves and readily fly when disturbed.  They feed by sucking sap and when infestations are large enough produce honeydew.  Infected plants have leaves that are stunted or yellow and may drop prematurely.

Management:

• Scout often and catch them early.  Deal with the pest right away to prevent populations from becoming unmanageable.
• Inspect new plants carefully and never introduce plants that have infestations to the home.
• Yellow sticky traps can be used to trap adults as they are highly attracted to the color.  Sticky traps will not be effective at eliminating the infestation but are very helpful in scouting the problem.
• Insecticides, like insecticidal soap and neem, can be used but are typically not as effective as you would hope.  Focus applications on the undersides of leaves.  Multiple, weekly applications are required to gain control.
• In many cases it is better to destroy heavily infested plants before they infest nearby plants.  This is particularly true for this very mobile pest.

More Information About Diagnosing Houseplant Problems