Before moving houseplants in for the winter, inspect them

Q. How do I keep unwelcome guests out of my houseplants?

A. Always check your plants for insects before bringing them into the house. Many natural predators exist outdoors, such as ladybugs and lacewings larvae, which keep the pest population low. Indoors there are no predators and two types of pests, leaf-dwellers and soil-dwellers, can be a problem indoors.

Leaf-dwellers that attack plants include aphids, spider mites, scale and mealybugs. Aphids are small globular insects. They travel in herds along stem tips. Aphids infest many plant types.

Scale appear as brownish helmets less than an eighth of an inch long. Their favorite hangouts include fig trees and ferns. Spidermites form tiny webs on the backside of leaves or where the leaves attach to the main branch. If spider mites are suspected, place a white paper under the leaves and tap the leaves gently. The spider mites will be visible on the white paper.

Other hitchhikers might be spiders, gnats or lacewings. You might also see insects at the intersections of leaves and stems.

Symptoms of houseplant pests are yellow or brown leaves, dropping leaves, stunted or distorted growth, and sticky leaves. Sap-feeding insects such as aphids and scale excrete a sweet, sticky substance called honeydew.

Soil-dwellers include slugs, sow bugs, earwigs, fungus gnats and ants.

For plants in small containers, gently slip the plant from the pot and examine the soil. Typically slugs, sow bugs and ants will be visible on the outer layer of soil near the drainage holes, flick them off with a finger or stick.

Pests like fungus gnats and earwigs typically dwell in the upper soil regions. Remove any dead foliage or flowers from the soil surface.

An easy way to remove insects is to hose down plants. It's best to use a hose with a nozzle so you can direct water underneath foliage. Apply a gentle spray; too hard a jet will not only dislodge insects but likely tear leaves from stems.

For small specimens, consider dunking the entire plant into a 5-gallon bucket of water for 15 minutes. This will cause insects on leaves or in the soil to flee. Add a few drops of liquid dish or hand soap to the water as a further deterrent to insects.

For houseplants in large containers, apply an insecticide to the soil surface and also to soil inside drainage holes.

A commercially prepared insecticidal soap is a good product to use if there are spider mites or aphids. For the unseen eggs lurking below the foliage, a systemic insecticide drench while your plants are still outside is recommended. The insecticide will move up into the canopy of foliage just in time for hatching eggs. The juvenile insects will not be able to become established on a treated plant. Be sure the insect you wish to control is on the label and to follow label instructions carefully.

Another option is to get a bag of soilless potting medium, water, some clean pots and repot. If you take the time now, it will be a fraction of what it take to conquer an insect problem that migrates onto other plants indoors. Once plants are moved indoors, keep them isolated for about six weeks and make visual inspections to ensure pests are gone.

- Terri Passolt

• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines, and University of Illinois Extension, North Cook Branch Office, Arlington Heights. Call (847) 298-3502 on Wednesdays or email northcookmg@gmail.com. Visit web.extension.illinois.edu/mg.