University of Illinois Extension

Bugged Houseplants

“When bringing garden plants inside for the winter, you can bring unwelcome guests as well. Anyone who has houseplants that were set outdoors for the summer and has now returned them to the window sills, greenhouse windows, and sunny foyers needs to be on the lookout for insect outbreaks on their houseplants,” says Richard Hentschel, U of I Extension horticulture specialist.  “While most gardeners usually spray or treat their houseplants a week or two before bringing them indoors, it is easy to miss getting complete coverage, allowing the insects to survive.

“Once indoors without any natural predators that might parasitize or eat them, they are free to feed and multiply on those houseplants. Besides the insects that make it inside on the foliage, there are those creepy crawlies like ‘pill bugs’ or ‘earwigs’ that are in the soil in the pot and will venture out looking for other food sources.”

Ants, too, may emerge, though they are unlikely to continue to survive, he added.

Even if you sprayed, insect eggs may not have been controlled--just the adults and nymph stages. Once the egg masses have been inside for just a few weeks, they can hatch and begin to cause trouble. The earlier you brought the houseplant indoors, the sooner in the fall you will see evidence of insects.

“One of the smaller insects and technically not an insect but a mite is the spider mite,” he said. “Spider mites seem to flourish in hot, dry weather outdoors and will do the same once inside with our drier, forced-air heat that is found in most homes. Their feeding damage is the same yellowed, speckled spots on the foliage. Since there are no breezes in the home, a good telltale sign is the ‘spider-webbing’ you will see in the leaf stem angles, and along the mid-vein of the leaves and near the newly forming buds.”

That, he added, is one way they spread from one plant to another.

Other typical insects found on houseplants are wooly aphids and mealy bugs--think aphid with a fur coat--and scales.

“Scales are the most difficult to control as they have a protective layer--scale--covering their soft bodies, that prevents sprays from reaching them,” he said. “If you have a houseplant with scale already established, the best advice may be to throw the plant out and not spread the scale to other plants in your home.”

Ranking from easiest to hardest to control goes aphids, mealy bugs, spider mites, and scale.

“There are many products available to the homeowner to control indoor plant insects,” he noted. “Some are liquid sprays, others are in aerosol form. Some control on contact, others are absorbed by the plants, and the insects like scale are controlled systemically.

“A word of caution is in order as not all products are safe on houseplants. You should read the label very thoroughly before you buy and use the control product.”

A good strategy is to clean the foliage monthly with a sprayer on the sink. If the plants are too large, perhaps the bathroom shower will work. This provides the opportunity to keep them dust free, allowing better food production and the opportunity for you to inspect the houseplants and get a jump on any insects bugging your houseplants.

“If you have insect-free houseplants, use caution when receiving and keeping holiday plants,” he said. “They may harbor insects and, when intermixed with your existing houseplants, can spread throughout your plants.

“If you suspect your gift plants may have insects, keep them separated and do not keep them past the holiday season.”