Q: I noticed some white flies hanging around my houseplants yesterday and was wondering if these are a problem?

— Eva Rodriguez, Chicago

A: Your description indicates an infestation of whiteflies, which are a common problem on houseplants. Adults are wedge-shaped with white, powdery wings, and they will fly up from the foliage in a cloud when a plant with a large population is disturbed.

Whiteflies will rest on the undersides of leaves, so you should always look under the leaves when purchasing new plants to make sure this pest is not present. It’s also a good practice to monitor under the leaves of your houseplants going forward, as it is easier to eradicate this insect when you catch it at an early stage.

Most gardeners discover whiteflies after the population has built up and they notice them flying around the plant, as you have, after brushing the foliage. This piercing-sucking insect feeds on the host plant’s nutrients and will continue reproducing throughout the year in a home or greenhouse. Generally, they are not a problem in the outside landscape in this area.

A large population of whiteflies can cause stunted growth and defoliation of houseplants, so you will need to take steps to control this pest. In addition, leaves can become covered with a sticky substance called honeydew that is secreted by whitefly nymphs and adults feeding on the plant. A black, sooty mold can grow on this honeydew, which is an indicator that you have an insect problem. The sooty mold does not damage the leaves but is unsightly.

As with most gardening pests, healthy, vigorous plants will be less susceptible to infestation and damage than plants under stress from improper culture. So start by making sure you are caring for your plants properly.

It is too cold outside now to take your plant outside and hose it off to disperse the adults. You may be able to carefully vacuum up the flying adults when disturbed, but be very careful not to damage the foliage by getting too close with the vacuum.

Commercially available traps, with at least one trap per two plants, can be effective in controlling mild infestations. After the adults are attracted to the yellow color on the card, stick the adhesive on it.

You can use an insecticidal soap to spray your plants to help control the population. Make sure you spray under the leaves, as this product works by contact.

The life cycle of a whitefly is about 30 days, and the actual duration will depend on the air temperature, so you will need to spray an insecticidal soap once a week for four to five weeks to get the population under control.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org

. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.