As a plant parent, coming to terms with the fact that our plants are a part of a larger ecosystem is important to us to maintain realistic standards of plant care. Grown and cultivated in soil from outdoor conditions, then brought indoors, sometimes, we may notice insects in our plant’s soil, leaves, or stems. But how can we differentiate beneficial insects from those that are pests? Here’s our list of indoor houseplant pests and how you can treat them.
Photo: Taro (Colocasia esculenta): Aphids tended by ants, Scot Nelson
Ants are not so much of a pest to our plants as they are to us. They can be annoying if they move into our houseplants and attempt to set up colonies. Often times, though, they come from a larger colony outside of the home. Ants also harvest honeydew, which is produced by true indoors houseplant pests such as aphids, mealybugs and whiteflies – Which they may protect, and even carry to other plants. Watch it in action in the video below.
Treatment: Ants can be controlled through baiting and insecticidal soap. Commercially available products are available for the treatment and removal of ants, such as ant bait and ant gel.
Photo: Cabbage leaf: Aphids, Scot Nelson
Aphids are soft-bodied, sap-sucking insects. While they may be harmless in small populations, left uncontrolled, they may cause leaf curl or stunted growth on plants. Most aphids reproduce asexually and birth live young. They love soft leaves and plants that are high in nitrogen and will secret a sticky fluid known as honeydew as they feed. This honeydew is sweet and attractive to ants, which may protect the aphids (their food source!), making population control more challenging.
Treatment: Aphids can be treated with an application of diatomaceous earth, or with neem-based plant products. Heavily infested plants should be pruned and disposed of to avoid infection of neighbouring plants.
Photo: Monarch butterfly larva, Scot Nelson
Caterpillars may appear on newly introduced houseplants, especially if they were cultivated or grown in outdoor garden centers. Butterflies lay their eggs on the undersides of plant leaves that hatch, and the caterpillars often deal damage to foliage due to their voracious appetites, creating holes in leaves. However, butterflies rarely fly into indoor apartments, so caterpillar problems can be easily overcome.
Treatment: Inspect your new plant and remove any caterpillar eggs. If the caterpillar has already hatched, being observant will help you identify affected plants. Caterpillars can be easily removed and disposed of, or set free outdoors.
Photo: Dark-winged Fungus Gnat, Katja Schulz
Fungus gnats are common in indoor houseplants and can often become a problem where humidity is high and soil is damp. While the adult flying form is harmless, it is the fungus gnat’s larval stage that deals the most damage to our plants as it feeds on organic material and root hair.
Treatment: Mosquito bits (containing BTI, or Bacillus thuringiensis var. israelensis) are the most effective way to treat fungus gnats and can be diluted in water and applied to the soil. Other methods include flushing the soil with hydrogen peroxide, or setting up yellow sticky traps for the adult fliers.
Photo: Leafminers on a weed, Scot Nelson
Similar to fungus gnats, leafminer adult flies are relatively harmless – Instead, it is their larval stage that deals damage to indoor plant foliage. After laying their eggs on the undersides of plants, worm-like leafminer larvae emerge, creating tunnel-like damage between the upper and lower layers of leaves that reduces the aesthetic value of plants and restricts growth.
Treatment: While most healthy plants will be able to resist or withstand leafminer damage on its own, prevention is the best medicine when it comes to battling leafminers. Inspect plants often and remove any leaves at the first hint of infestation. Wash the undersides to remove any eggs.
Photo: Plumeria: Mealybugs, Scot Nelson
Photo: Hibiscus: Mealybugs on flower, Scot Nelson
Mealybugs present as white, cottony and slow-moving insects that can be found frequently hiding on the undersides of leaves or stems. They are slow-moving, cannot fly, and feed by sucking sap out of plant tissue. Damage presents as leaf yellowing or plant weakness in high mealybug populations. Like aphids, mealybugs may leave behind a sweet, sticky residue ccalled honeydew.
Treatment: Small mealybug populations can be treated with a solution of alcohol and water, dabbed on with a cotton Q-tip. Insecticidal soap and neem oil are also effective ways of treating mealybugs.
Photo: Awa: Root Mealybug — closeup of root damage, Scot Nelson
Root mealybugs resemble mealybugs in that they present as white cottony masses, the only difference is that they lurk below or on the soil line. They are much more difficult to spot as they are very small, and often go unnoticed because they are often the same colour as soil and deal root damage, leaving plants susceptible to problems such as mildew.
Treatment: Root mealybugs can be treated with a hydrogen peroxide soil drench to kill of any eggs or larvae. It is also good to remove as much of the old soil as possible, wash off and soak the roots with tepid water, before repotting into fresh soil mixed with diatomaceous earth.
Photo: Scale Insects, Scot Nelson
Scale insects are slow-moving, hard or soft-shelled insects. They will resemble small bumps on your plant, and if discovered in small amounts, can be easily scraped off by hand. In large numbers however, they can deal damage to your plant.
Treatment: The best way to remove scale insects is to prune off heavily infested parts of a plant. They can also be removed with an alcohol solution and a Q-tip, or treated with neem or horticultural oils.
Photo: Achatina fulica (Giant African snail), Scot Nelson
Snails are both friend and foe! In controlled populations, they help to eat up damaged, rotting leaves, various bacteria and fungi. If left uncontrolled, they can deal foliar damage, just like caterpillars, to leaves. They are especially fond of new leaves and make up a critical part of a tiny ecosystem!
Treatment: While rare, you are dealing with a large snail population amongst your indoor potted plants, snails can be treated with diatomaceous earth, salt or a vinegar spray. You should also remove snail trails so that other snails do not trace them.
Photo: Carmine spider mites, Scot Nelson
Spider mites are small, almost microscopic arachnids (closely related to spiders) that deal damage to your plant by piercing leaf tissue and sucking up the plant fluid. Spiderr mite damage often presents as faint speckling on leaves and are commonly found where the growing conditions are arid and warm. They are extremely adaptable and quickly gain immunity to chemical pesticide, and their population can quickly grow out of hand if uncontained. A large infestation will present with fine webbing and quickly yellowing leaves.
Treatment: Spider-mite infested plants should be washed down often to knock off as many mites as possible. They can be treated frequently with a neem-based application thoroughly, on all plant surfaces. Stressed plants are often the best host for spider mites, and the best way to prevent them is to ensure your plants are inspected and cleaned regularly to prevent dust build-up (spider mites are windsurfers and can easily spread to other plants!)
Photo: Thrips on a leaf, Scot Nelson
Thrips are small, thin-bodied insects that damage plants by sucking their juices. They are persistent and cause foliarrr damage (silvery pale leaves). Thrips are also fond of new growth, and will often deal damage to newly unfurled leaves, causing them to emerge twisted, disfigured, or shrivelled. Thrips lay their eggs in the soil of plants and cut slits in the stem of plants, laying eggs in them, so it is important to be extremely vigilant to prevent against heavy infestations.
Treatment: Like spider mites, thrips are best knocked off plants with a strong spray of water to keep populations under control. They can also be treated with neem. New leaves should be frequently inspected (especially if they are taking longer than usual to unfurl) for signs of thrip larvae, and pruned quickly if discovered.
Photo: Whiteflies, Scot Nelson
Whiteflies are sap-sucking insects that secrete honeydew. In the nymph and adult stage, whiteflies suck sap from plants, causing stunted growth, leaving plants susceptible to disease. They are best recognized as they fly, creating clouds around plants when disturbed. As juveniles, they resemble scale insects and can be hard to spot due to their translucent colour.
Treatment: Adult whiteflies can be removed with sticky traps. Young whiteflies can be knocked off plants with a strong blast of water, and treated with insecticidal soap, horticultural oils or neem-based products.