URBANA, Ill. — Keeping houseplants is a hobby that has recently seen a huge resurgence. Now, nurseries that were all but shuttered for the winter are hosting houseplant parties and other events to help people keep their hands dirty all year long. Tending to houseplants is a way to maintain our connection with the natural world when conditions aren’t conducive to outdoor gardening, such as in the winter, for apartment dwellers, or just for those who don’t have time to maintain larger landscaping beds. Houseplants offer a wide variety of colors, textures, and requirements to fit anyone’s tastes and situation. But what do you do when things go wrong?

Healthy Plants are Better Able to Resist Pests 

The first thing to remember is that, like humans, healthy plants can better resist disease. Keeping plants properly watered and fertilized and repotting them, when necessary, will help to ward off unwanted guests. Frequently monitor plants to catch infestations early when they are more treatable. Closely inspect the soil, top, and undersides of leaves, and stems for anything unusual, such as discoloration, damage, or other evidence of pests. Using yellow sticky traps can also help to monitor for bugs. A hand lens can be useful in identifying pests. However, modern cell phone cameras are also great for enlarging images of bugs. Below are some pests to watch out for.

Fungus gnats cause little damage to plants but can be a big nuisance. They prefer damp areas, so this may be a sign plants are being watered too frequently or that standing water is being left in condensation trays. Many indoor gardeners become frustrated with fungus gnats due to the difficulty in treating them. Many insecticides are ineffective against them because the larvae spend much of their time in the soil, and adults are highly mobile. Yellow sticky traps can help prevent egg laying, but the best control is letting the top 2 to 3” of the soil dry out between watering. If they persist, the potting medium can be changed out entirely, rinsing the roots before repotting to remove any stragglers.

Scale insects are sometimes mistaken for leaf spots, as they often form a covering to protect the soft-bodied insect inside. They may align along leaf veins. There are many types of scales, including soft scales and armored scales. Soft scales suck plant juices and secrete honeydew, a sticky substance that will often lead to sooty mold. This will cause the leaf to appear to have a powdery black coating. Armored scales do not produce honeydew. Feeding from any scale insect can cause yellowing of leaves, stunted growth, dieback, and death of the plant. For a small infestation, scale insects can be scraped off with a fingernail or toothbrush. Depending on the type of scale, horticultural oils or systemic insecticides may be effective.

Mealybugs are a type of slow-moving scale that feeds on plant juices. The first sign of mealybugs is a white, cottony substance often seen on leaves. Because they can hide in tiny crevasses, mealybugs can be difficult to eradicate, but it can be done with some dedication. Dip a cotton swab in rubbing alcohol and wipe down any cottony spots. This will desiccate the bugs. Follow this with a horticultural oil to smother any that were missed. Check the plant every few days for new signs of bugs. Severe infestations may require the use of a systemic insecticide. 

Thrips are tiny and can be difficult to spot. If the leaves have irregular silver patches and/or small black fecal specks or distorted flowers, the plant may have thrips. Thrips spend part of their lifecycle in the soil, so repeated treatments, including the soil, may be required. 

If the use of insecticides is warranted, first, isolate infested plants to protect other plants from also becoming infected. Once a positive identification of the pest is made, look for insecticides labeled to treat the culprit and follow all label directions. Frequent monitoring of the plant afterward is required, and repeat treatments may be needed to fully eliminate the infestation. Do not bring the plant out of isolation until the pest has been completely eradicated.

For more on houseplant pests, connect with a local University of Illinois Extension office from the statewide map.

Jamie Viebach is an Illinois Extension horticulture educator for DuPage, Kane, and Kendall counties. Gardeners Corner is a quarterly newsletter from gardening experts around the state. Each issue highlights best practices that will make your houseplants, landscape, or garden shine in any season. Join the Gardener’s Corner email list at subscribe for direct access to timely tips.

Photo Caption: Mealybugs are one type of pest that can be found in indoor houseplants. Photo by Jamie Viebach, Illinois Extension.