University of Illinois Extension

Bugs in Houseplants

After homeowners bring their indoor houseplants inside to avoid freezing temperatures, they may discover some “passengers” that hitched a ride, said a University of Illinois Extension horticulture specialist.

“Indoor temperatures and the time inside allows insects that would otherwise be dormant to come alive or insect eggs to hatch,” said Richard Hentschel. “Some of these insects belong outdoors and do not thrive inside in the dryer, warmer temperatures. These insects frequently will be found dead on window sills or near the plants.

bugs“There are others that not only thrive outdoors, but on our houseplants indoors just as well or perhaps better.”

Scale insects are one group in that category. These insects spend much of their lifecycle protected under a covering which keeps them from drying out and protected from our efforts to control them.

“Scale insects stay alive by using the sap from the houseplant for breakfast, lunch, and dinner,” he said. “That protective covering or scale makes them difficult to manage as topical treatments will not penetrate the scale.

“On the plus side, the scales are immobile at this stage and can be easy to spot. Indoors, the scale insects have no natural predators, no rainstorms or high winds to keep them in check, and this is why they can multiply so quickly.”

Hentschel noted that scales do have a “creepy-crawly stage” just after they hatch from eggs under a female scale. This is the time they are very vulnerable to topical treatments as they have not developed their protective covering.

“They will be small crawlers, moving upwards usually to newer, tender growth on the houseplant,” he said. “If you catch them at this time, you can rinse them off the plant at the kitchen sink using the sprayers attachment or in the shower if the plant is too big for the sink.”

Scales can be found on plant parts both above and below the soil.

“You may have treated the plants before you brought them in and the foliage and stems appeared free of insects,” he said. “The scales lurking under the soil continued to survive and eventually go to the above-soil plant parts.”

These insects can be found on just about any houseplant, he noted. Pothos, fig trees, ivy, spider plants, schefflera, and ferns are just a few examples.

“You will find them as miniature helmets, often similar in color to the plant’s stem or living just below the soil surface on the roots of the plant,” he said. “You won’t see any legs, eyes, or body parts that even resemble an insect. You may see clear, sticky spots of sap on foliage or even the floor or window sill. That is a sign you have scale insects feeding.”
Other insects, such as aphids, can also produce these symptoms.

“Unlike other houseplant insects, treatments for scales will need to be applied for three to four months to be sure you have controlled all the crawlers and adults,” Hentschel said. “Insecticidal soaps are a good choice along with a variety of aerosol and pump sprays. Be sure the insect you wish to control in on the label.

“A word of caution is in order as not all products are safe on houseplants. You should read the label thoroughly before you buy and use any control product. Label instructions should also be closely followed regarding where you treat, most often in a well-ventilated area.”