Thrips, scale insects, and spider mites! Identify and control houseplant pests
Stay vigilant, act quickly, and consider biological control. Learn how to eliminate houseplant pests before they take over with these detailed illustrations and practical tips.
Keep a close eye on your plants!
- Use a loupe or magnifying glass to examine the undersides of leaves, leaf axils, and growing points, and look for any damage in the middle of leaves. A helpful trick is to photograph the plant with your phone or camera and enlarge the image. Sticky spots on the plant or soil may indicate pests that secrete honeydew.
- Place yellow sticky traps near your plants to monitor for thrips, whiteflies, aphids, and fungus gnats.
- Always inspect new houseplants and keep them separate from your other plants for at least a month. Avoid placing cut flowers, potted herbs, and fruits near your houseplants.
- In spring, increased light levels cause houseplant pests to multiply rapidly, making control more challenging. Grow lights may also promote their reproduction.
Act quickly to control pests
- Quickly isolate any plant you suspect may have pests. Identify the pest and its habits to choose the best control methods.
- The sooner you tackle the pest, the better your chances of success.
- If a plant is heavily infested, you might consider disposing of it. Many pests are resilient and may require multiple treatments with pesticide. Moreover, products don’t affect all life stages of pests, like eggs, or adults hiding under webs, wool, or scales.
- If possible, start by removing leaves and plant parts infested by pests. If the plant tolerates cutting, prune it to make control easier.
- When using a diluted pesticide and the plant is small, immerse the top part of the plant into the solution and keep it there for several minutes. To enhance the effectiveness of a spray pesticide, place the plant in a plastic bag during treatment.
Is washing with water beneficial?
Regularly washing with water is most effective against aphids, whose life stages are all on the surface of plant tissues. It can also reduce the number of spider mites. However, thrips may actually benefit from moisture and spraying.
Don’t enhance the treatment with detergents or soft soap, as they are not approved as pesticides. Soap solutions can remove the protective wax layer from leaves, which may harm the plant and help the pests.
Try biological control
Biological control uses nature’s own beneficial organisms to eliminate plant pests. These control organisms are harmless to humans and animals, offering a natural alternative to pesticides. Biological control is suitable for home settings and greenhouses, though using flying control organisms isn’t recommended in very open spaces. Monitoring your plants is key to success, as beneficial organisms should be introduced as early as possible when pests appear.
Choose an approved product
If you’re considering using a pesticide, you can refer to the Plant protection products register at kemidigi.fi/kasvinsuojeluainerekisteri. Select a product that’s approved for indoor use and effective against the specific pest, and be sure to follow the instructions. Keep in mind the withholding periods of pesticides when using control organisms.
Houseplant pests: red spider mite
Identify: About half a millimeter in size and varying in color, the red spider mite is difficult to see with the naked eye. It lives under webbing on the undersides of leaves and in leaf axils.
Damage: Yellow spots appear on the upper surfaces of leaves, and leaves gradually yellow and wither. Thrives in dry and warm indoor air and spreads to new plants via webbing.
Favorite plants: Many species, such as calatheas, ivies, and cast-iron-plants.
Control: Challenging because the pest can overwinter on the plant, in the pot, and on plant supports, starting to reproduce in spring. Spraying the undersides of leaves impairs the mites’ living conditions. You can spray the foliage of the plant with the oil-based product Carbon Kick Booster approved for organic production. Biological control: predatory mites Phytoseiulus persimilis and Neoseiulus californicus.
Houseplant pests: aphids
Identify: Insects 2–4 millimeters long, visible to the naked eye, living in dense colonies on young parts of the plant, undersides of leaves, and buds. Coloring varies by species, conditions, and diet.
Damage: They suck plant sap, causing stunted growth and distorted shoots. Buds may fail to open. They excrete honeydew and can transmit viral diseases.
Favorite plants: For example, hibiscus and potted roses.
Control: Being soft-bodied, they are easy to control by spraying with water several times. Biological control: lacewing larvae and two-spot ladybirds, which are effective predators of aphids.
Houseplant pests: greenhouse whitefly
Identify: A white insect 1–2 millimeters long, lives on the undersides of leaves and takes flight when the plant is disturbed.
Damage: Sucks plant sap, causing young parts to become deformed. Excretes sticky honeydew.
Favorite plants: Especially soft-leaved species, such as hibiscus, poinsettia, and fuchsia.
Control: Requires multiple treatments with pesticide. Biological control: yellow sticky traps for monitoring whiteflies and controlling flying adults, predatory mites Amblyseius swirskii, and parasitic wasps Encarsia formosa.
Houseplant pests: scale insects
Identify: Mealybugs are covered with cotton-like waxy wool, while scale insects are protected by a hard brown or pale shell. These stationary and visible bugs live on the undersides of leaves, in leaf axils, and on stems, and excrete honeydew.
Damage: They suck plant sap, causing stunted growth and leaf deformities.
Favorite plants: Hard-leaved and waxy-surfaced plants, such as palms, figs, citrus, orchids, and cacti.
Control: Requires persistence, as the adult lays a huge number of eggs under the scale or waxy wool. You can enhance the effectiveness of spray pesticides by removing the scale insects before treatment. Wash hands and tools carefully to prevent tiny larvae or eggs from spreading to new plants. For biological control of mealybugs, use mealybug ladybirds and pheromone traps. Currently, there is no biological control method against scale insects.
Houseplant pests: thrips
Identify: An oblong pest about one millimeter long, distinguishable with a magnifying glass. Color is gray, brownish, black, or mottled, with light fringed wings. Young individuals can be easily mistaken for foxglove aphids.
Damage: They suck sap from plant cells, causing light or silvery streaks on leaves, growing points, buds, and flowers. Leaves and flowers may wither.
Favorite plants: Palms, peace lilies, ficuses, and many flowering plants. The common thrips species in Finland are nearly omnivorous.
Control: Control is challenging because thrips live in sheltered places and lay eggs inside plant tissues. They also pupate in the growing medium. Avoid leaf spraying. Biological control: blue and yellow sticky traps for monitoring thrips and controlling adults, thrips predatory mites, and Orius bugs.
Sources: Biological control expert Katrianna Leino, Tarhurinapu, Biotus.
