From the Potting Bench: Common Insects on Houseplants

Spider mites are tiny arachnids, usually white or reddish, that are hard to see until there’s a large population. Look for fine webbing housing the mites along the leaves and stems. Spider mites can be hard to control. In optimal conditions they can reproduce in as little as 6 days, so be diligent with your treatment. A horticultural spray oil like Bonide All Seasons works by smothering all stages of mites, including eggs. It’s recommended to spray weekly at least three times to kill all present generations. Focus spray on undersides of leaves and along stems. Pro tip: lay out plastic or a sheet to protect walls, flooring, and furniture around your plant from overspray, the oil can stain!

Aphids are usually green or yellow on houseplants, but can be black. They’re small (1/8 inch long), pear-shaped insects that are often found in clusters along areas of new growth on plants. These clusters reproduce quickly, giving birth to live female clones that often have the next generation developing within them already, no males needed. They secrete a sticky, sap-like substance called honeydew as they suck on plants, which can develop patches of sooty mold. Organic sprays like Insecticidal Soap are safe to use inside, working by smothering the insects but also penetrating their cells, causing desiccation. Spray weekly for several weeks to prevent new generations from reproducing. For major infestations, consider using a systemic like Bonide Systemic Houseplant Insect Control, which will kill anything that sucks on the plant for up to 8 weeks. This chemical will be present in all parts of the plant, so don’t use it on edibles or blooming plants that pollinators might visit.

Thrips are larger than spider mites, but smaller than aphids. If you look closely at the aphid photo, the smaller white insects are thrips. They are elongated and look rectangular to the naked eye. They usually are found in large groups. Like aphids, female thrips can produce clones without a male present, so their populations can grow exponentially. Horticultural spray oil, insecticidal soap, and the systemic houseplant insecticide are all effective on thrips.

Mealybugs are usually a little larger than aphids, white and fluffy-looking. They’re found in colonies along the stems of plants, especially hiding in the crevices where leaves grow out from the stem. They secrete honeydew like aphids, so watch for patches of sooty mold to alert you to their presence. They take longer to reproduce than the smaller insects, but still need repeated treatments to control multiple generations. Horticultural spray oil, insecticidal soap, and the systemic houseplant insecticide are all effective on mealybugs.

This time of year, we get a lot of calls about little black fungus gnats in houseplants. They aren’t particularly damaging to plants, but they can be annoying flying around your home. Sprays are not usually very effective, but yellow sticky traps will attract and trap the adults. Bonide Systemic Houseplant Insect Control will kill the larvae feeding on the plant roots. We use a combination of the two products for major infestations.