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Houseplants: Insect Pests and Their Control

Routinely dusting leaves is important to a plant's health.

Routinely dusting leaves is important to a plant's health.

Houseplants Have Many Benefits

Keeping houseplants is popular around the world. They bring a little of the outdoors in and add aesthetics and cheer to sterile environs. For those of us who can't have pets, plants give us something to nurture and watch grow. They have health benefits too. Houseplants have been shown to relieve stress and purify the air.

How to Keep Plants Healthy

Houseplants generally thrive in temperatures around 70 degrees and dislike being placed near heater or A/C vents. Some tolerate low-light conditions while others like indirect sun. Water needs may also vary. When choosing plants, consider toxicity to pets.

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants


To ensure the health of indoor plants, here are some general tips:

  • Choose for the plant's preferred growing conditions.
  • Quarantine apart from other plants for the first week at home. Pests can hitch a ride from nurseries and stores.
  • Make sure your containers have unobstructed drainage holes.
  • If repotting, use a sterile potting medium and a clean container about 2" larger in diameter. Too large a pot will prevent good root structure.
  • Use a moisture meter and water thoroughly when needed. Preferences vary by plant type.
  • Remove standing water from trays to ensure good aeration.
  • When moving a plant, give it time to acclimate. Avoid direct sunlight.
  • Routinely clean leaves and remove any dead or yellowed growth.

Even under the best care, houseplants can still get pests. The most common include aphids, fungus gnats, mealybugs, scales, spider mites, thrips, and whiteflies.

Solanum aphid

Solanum aphid

Aphids

These sucking insects are easily seen and vary in color from green to gold and pink to black. As they quickly grow, they leave behind shed exoskeletons that look like white specks. Damage from sap-sucking aphids includes curled and distorted leaves and stunted growth.

Aphids produce honeydew which can lead to sooty mold on leaves that look like black spots. This should be washed off since it can block photosynthesis and weaken the plant.

Control

  1. Wash off with a good blast of water. Aphids are easy to squish by hand.
  2. Apply insecticidal soap. The fatty acids in it kill the insects quickly.
  3. Use neem oil. It works as a growth interrupter and stops reproduction within a few days.

Ants and Honeydew

In the same category of honeydew producers are scales, whiteflies, and mites. It is common to see ants come and farm these insects for their sticky exudate.

Ants may be the first sign of a problem and will likely need to be controlled too. Boric acid, diatomaceous earth, Tanglefoot barrier, and pyrethrin are some options. Treatment is effective at both home-entry points and near the affected plant.

Yellow sticky traps work well for flying insects and can be easily attached to small stakes.

Yellow sticky traps work well for flying insects and can be easily attached to small stakes.

Fungus Gnats

Fungus gnats make themselves known by visibly flying around houseplants. They look like tiny mosquitoes and prefer damp, humid conditions. They lay their eggs in the soil which hatch into tiny larvae. It is important to break the cycle of reproduction.

Control

  1. Correct the excess moisture conditions in which they thrive.
  2. Place yellow sticky traps within the pot to catch the adult flies.
  3. Eggs and larvae can be smothered with a top dressing of horticultural sand.

If these basic controls don't work, a soil drench containing Bacillus thuringiensis, var. Israelensis can be used. This Bti can be found at a garden center in liquid form or as mosquito dunks or chips. If solid, they will need to soak and steep before application, then applied. Once the mixture has saturated the soil, let it drain thoroughly.

It is important to make sure that the plant is healthy and not affected by root rot before this treatment.

Mealybugs look like cottony clusters at stem junctures and the bases of plants.

Mealybugs look like cottony clusters at stem junctures and the bases of plants.

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Mealybugs

Mealybugs are the most common pests of succulents, cacti, orchids, and palms. These white, cottony, soft-bodied insects can sometimes be confused with soft scales. If caught early, they can be easily eradicated.

Control

Infected areas can be carefully pruned out and Isopropyl alcohol can be directly applied with a cotton swab. For larger infestations, insecticidal soap is recommended.

There are other formulations and some homemade alcohol/soap water mixtures. I prefer those with known studies so I don't harm my plants. it is always important to read the labels and make sure they are used correctly and are marked safe for houseplants.

Scales can be hard or soft-bodied, honeydew producing insects, often seen with sooty mold.

Scales can be hard or soft-bodied, honeydew producing insects, often seen with sooty mold.

Scales

Scales fall under the category of sucking, honeydew producing insects. As with aphids, they are accompanied by sooty mold and ants. They are often picked up when plants have been moved outside. When immature, they are not noticed. It's ant activity, sooty mold, or the mature brown bumpy shells on plant stems that grab one's attention. If infestations are heavy, leaf tips will look distorted, and the plant will look weakened.

Control

Scales can be easily scraped off. They can also be treated directly w/ full-strength isopropyl alcohol on a cotton swab as long as it gets to the insect under the protective shell. Once mature, these insects are immobile, yet resistant to spray insecticides.

Insecticidal soap easily works on the immature scale before it develops a protective shell but must reach the actual insect which can be challenging.

Systemic controls that the plants take up into its cells will target any insects that feed on it. This makes it an option for these sucking insects on non-edible plants. Bonide Systemic Houseplant Insect Control is an example. Since plants are kept inside, harm to pollinators is unlikely. Always follow label instructions.

The label is the law.

Spider mites form tiny webs and look like chili powder.

Spider mites form tiny webs and look like chili powder.

Spider Mites

Spider mites are tiny but mighty and have caused the demise of many plants. It's best to treat them immediately since the damage is well underway to plant cells by the time any signs are visible.

They are attracted to dry and dusty conditions. Early damage is seen as leaf flecking or stippling that looks like white pepper and black fecal specks. As populations increase, small webbing on leaf tips will be seen, and the mites will look like red chili powder.

Control

  1. Isolate the infected plant from healthy ones. Mites can travel via drafts of air.
  2. Correct the plant's environment w/ more humidity and use a mister.
  3. Trim out affected plant parts.
  4. Apply neem oil. This is not a contact insecticide but rather a growth inhibitor, so the effects take a few days.
  5. Remove any webbing and suction clusters of mites with a hand vacuum.

If damage is severe, it may be necessary to dispose of the plant.

Thrips are nearly invisible to the naked eye.

Thrips are nearly invisible to the naked eye.

Thrips

Thrips have become widespread in gardens and nurseries but are nearly invisible to the naked eye. Their presence is revealed through silvery stippling, stunted growth and distorted leaves. One can check for them by tapping a leaf over a white sheet of paper to see if they scurry away.

Thrips are hard to control because they lay eggs on the plant, and then the nymphs drop into the soil before emerging as adults. This is why neem oil is a good option. It interrupts sexual maturity and prevents reproduction.

Control

  1. Wash plants with a good shower.
  2. Remove affected leaves.
  3. Apply neem oil.
  4. Use yellow sticky traps or tape.

If these controls don't work, it may be necessary to use a systemic insect product like Bonide for Houseplants that contains imidacloprid, a neo-nicotinoid.



Whiteflies are elusive and resistant to spray insecticides.

Whiteflies are elusive and resistant to spray insecticides.

Whiteflies

Whiteflies are another of the honeydew producing and sap-sucking insects that target both indoor and outdoor plants. Favorite plants are begonias, poinsettias, and hibiscus.

They make themselves known by dispersing when disturbed, then quickly resettling on the undersides of leaves where they tend to eggs kept under their waxy exudate. The ants attracted by their sticky honeydew work to deter natural predators. Whiteflies also build a quick resistance to insecticides. They are hard to target and require a multi-faceted approach.

Control

  1. Raise humidity and mist leaves. This may work as a deterrent since they prefer hot and dry conditions.
  2. Remove affected plant parts.
  3. Use yellow sticky traps for adult fliers.
  4. Apply insecticidal soap or neem oil to undersides of leaves.

A systemic product like Bonide Systemic Houseplant Insect Control may be necessary for best results.

Use a Practical Approach

Work with nature and start with the least harmful methods. Although indoor plants are usually isolated from pollinators and beneficial predators, it is still a good practice to avoid strong pesticides. Consider the risks to children and pets.

Healthy houseplants will thrive with proper placement, consistent care, and good sanitation, making them naturally resistant to pests.

Resources

ipm.ucanr.edu

Cranshaw, Garden Insects of North America

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2023 Catherine Tally

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