Whether you have a large collection of houseplants or you are just starting to explore your green thumb, houseplant pests are something you will have to deal with, unfortunately. We know—it’s not what you wanted to hear, but the good news is there are measures you can take to prevent pests, as well as some tried and true ways to eliminate them.
The most common indoor plant pests include fungus gnats, spider mites, aphids, mealy bugs, scale, and thrips. A houseplant can get pests when you bring a new plant home, bring a plant indoors from outside, through open windows or doors, from a flower arrangement or bouquet, or from other sources. When plants are stressed or neglected, insect pests may become a severe problem in a short time. The best prevention is frequent cleaning and inspecting leaves and close observation of the health of your houseplants.
Come visit your local plant shop at one of our garden centers for personalized advice and to pick up both natural and conventional pesticide options.
Fungus Gnats
These are very tiny, dark gnats/flies that develop in moist potting soil; larvae feed on root hairs and fungus in the soil and emerge as flying adults every 30 days.
Signs: Tiny gnats flying around soil and/or plant.
Control: Allow the soil to dry out and use sticky gnat traps, sprinkle Diatomaceous earth on top of the soil to kill emerging adults, or treat with Mosquito Bits (Bti) by layering on top of soil or soaking in water. In extreme cases, remove as much soil as possible and repot into fresh, well-draining potting soil.
Tip: Fungus gnats are common after repotting if watering is not adjusted.
Spider Mites
Though not “true” spiders; these insects are very, very, tiny (about 1 mm in size, smaller than the period following this sentence). Adult mites reproduce quickly and usually lay eggs on the undersides of leaves near the stem.
Signs: Small red or brown dots on leaves, dull or discolored leaves, or a fine webbing that may make the plant appear dusty.
Control: Prevention is best since they can be difficult to control; keep plant foliage clean and dust-free by wiping every 2 weeks with water or neem oil. Isolate affected plant(s) and spray thoroughly with neem oil or insecticidal soap every 10 days until all signs of pests are gone. Prune off the most infested plant parts if possible. In severe cases, predatory mites can be purchased from beneficial insect suppliers and released to hunt and kill the spider mites in homes or greenhouses. The predators die off once their food supply is gone.
Tip: Plants in hot sun tend to get mites more than low-light plants. Certain species are more likely to have spider mites than others (croton, alocasia, bird of paradise, citrus, cast iron plant, palms, cordyline/ti plants, hibiscus, marijuana).
Aphids
A very common pest on outdoor plants, aphids can be found in a range of colors including green, black, brown, or yellow. They are small and can often be overlooked until population numbers are large. They suck on plant sap and can usually be found on new growth, stems, and flower buds.
Signs: Curling or crinkly leaves and damaged flower buds; small white exoskeletons are left behind as the insects grow. Shiny, sticky substance on foliage is caused by their excrement.
Control: Isolate and trim off leaves that are most affected. If possible, take plant outside and gently spray with water to knock off as many bugs as you can; once the plant is dry, treat with insecticidal soap or neem oil.
Tip: Always test a small, lower leaf with an intended product to be sure it won’t discolor or damage foliage. Some plants with fuzzy leaves like African violets or chalky-blue coloration such as echeveria may show discoloration from neem oil.
Tip: Avoid high-nitrogen fertilizers which may push soft, new growth that is extra vulnerable to aphids; a 3-1-2 ratio is preferred for most indoor plant fertilizers.
Mealybugs
Resembling small bits of cotton or white fuzz, mealybugs are destructive, sucking insect pests.
Signs: Spots on leaves, yellow leaves, leaf drops, weak stems, and slowed growth; shiny, sticky substance on foliage is caused by their excrement. Females can lay over 500 eggs over a 2-week period, young mealybugs are the most vulnerable to sprays and are easiest to control when immature.
Control: Isolate and treat with insecticidal soap or neem oil (both available in our plant stores); use a cotton swab or Q-tip dipped in alcohol to dab directly onto pests for hand removal. Use sticky yellow traps to catch during the crawling stage.
Tip: Cactus and succulents (Jade) are extremely prone to mealy bugs, as well as citrus, hoya, pothos, philodendrons, ferns, ficus, palms, and dracaena.
Scale
This is one of the most common pests on houseplants, especially citrus, ficus, schefflera, palms, and bird of paradise. Difficult to diagnose for the beginner, scale do not look like insects; they move very slowly as they suck the sap out of plant tissue. They appear to look like raised, brown bumps commonly found along plant stems and on leaf surfaces or undersides near the mid-vein; they can be gently scratched off with your fingernail.
Signs: “Honeydew” which is the shiny, sticky residue found on leaves that comes from their excrement. Occasionally a secondary issue can develop called “sooty mold” as the honeydew grows black mildew that discolors the leaf. Infested plants may also have weakened stems and slowed growth.
Control: Adult pests have a hard “armor” coating that is difficult to penetrate with sprays, but young, immature pests are easier to kill. Oil sprays (horticultural oil or neem) act as smothering agents to kill scale, but hand removal of large colonies can also be effective by brushing off with a soft toothbrush or cloth.
Thrips
Extremely small, winged brown or tan insects that feed on plant leaves, flowers, and buds.
Signs: Silver spots or dark patches on foliage and dark dots from their excrement. Thrips can cause weakened plant growth and brown, curling leaf edges, and can also spread viruses from one plant to another.
Control: Isolate the plant (thrips are very contagious) by using yellow sticky traps, neem oil, insecticidal soap, or Systemic Houseplant Insect Control (Imidacloprid).
Tip: The most common plants bothered by thrips include palms, dracaena, and aroids; most cactus and succulents seem to be exempt from thrips problems.
Troubleshooting Common Plant Problems
Leaf browning or wilting: This may be due to underwatering or low humidity; increase the humidity to help balance moisture needs.
Leaf yellowing: Yellow leaf tips or yellowing leaves that are lower or toward the inside of the plant may be caused by overwatering. Yellowing leaves toward the top of the plant may indicate too much direct light.
Spots on the leaves: Brown or black spots with a yellow or pale “halo” may indicate a fungal disease. Be sure to remove any yellow or spotty leaves by cutting with a sharp blade to reduce the potential spread of diseases and if possible, isolate the sick plant. Bring a leaf sample in a sealed bag to one of our experts at a garden center or plant shop for a diagnosis.
Common Pest Control Products
Insecticidal soap, Neem Oil, Horticultural Oil (mineral oil), Diatomaceous earth, Systemic Houseplant Insect Control (Imidacloprid), Total release insect bombs for indoors, rubbing alcohol, sticky yellow trap cards.
These and more are available at the plant shops in our garden centers, and our staff will be happy ot help direct you to the right treatment for your houseplant pests. Consider taking photos of your plant(s) in question and we’ll do out best to diagnose the issue!
