Indoor Insects That Are Sticky on Leaves

Honeydew

• The sticky substance gumming up your houseplants' leaves is honeydew. Several insects produce honeydew as waste while feeding on the plant's phloem. This sap, a mix of water and nutrients, flows continuously from the roots to the leaves of growing plants. The offending insects -- aphids, soft scale insects, mealybugs and whiteflies -- pump it from the plant's leaf and stem tissues with needlelike beaks. They metabolize its small concentration of nitrogen and excrete the carbohydrate-rich leftovers as honeydew. Prolonged feeding causes wilting and eventually kills the leaves, twigs and branches.

Pest Identification

• To identify the insects on your houseplants, examine their usual feeding sites on the branches, leaf backs and axils, where the leaves attach to the stems. Pear-shaped, green, yellow, red, brown or black aphids form large colonies and seldom move even if disturbed. Round or oval, often dome-shaped soft scales could pass as white, brown, reddish or black fungal growths. Populations of wingless, white or grayish mealybugs resemble clusters of cotton wool. White or yellowish, four-winged whiteflies swarm from the plants when disturbed.

Sooty Mold

• Indoor plants with honeydew-covered leaves lure airborne sooty mold spores. These spores feed on the honeydew and germinate into black, sooty fungal layers. Light sooty mold is a cosmetic problem. In dense layers, it may block the light the plants need for photosynthesis.

Cultural Control

• Before turning to chemical measures to protect your indoor plants, consider nontoxic alternatives. Pruning out the infested parts or taking the plants outside for spraying with the garden hose controls small numbers of aphids, mealybugs and whitefly larvae. Scrub scales off gently with an old toothbrush or scouring pad. Treat larger aphid, scale and mealybug populations by washing the plants with a soft brush dipped in a mix of 2 teaspoons of mild detergent soap in 1 gallon of water, paying extra attention to the leaf undersides and stems. Remove large adult whitefly colonies with a handheld vacuum, freeze them overnight and dispose of them in a sealed container.

Insecticidal Soap

• Insecticidal soap reduces insect infestations without being toxic. Make a solution of 5 tablespoons of liquid, detergent-free soap and 1 gallon of soft water and place your plants in a sink or bathtub. Spray them to the runoff point so both sides of the leaves are covered. Treat them early in the morning or at night to increase drying time. The soap must reach the pests to kill them, so repeating the treatment twice over the next week ensures you'll kill most of the remaining insects.