Question:
The leaves on my houseplant are covered with a sticky sap. There are also small "bumps" on the stems. What is the problem?Answer:
The houseplant may be infested with scale insects. These small, inconspicuous insects are covered with shell-like coverings. They attach themselves to stems or leaves and suck sap from the plants. As they feed, the scale insects excrete a sweet, sticky substance called honeydew. The honeydew accumulates on the plant’s lower foliage, furniture, carpeting, or other objects beneath the infested plant.
The life cycle of scale insects consists of the egg, nymph, and adult stages. Eggs are laid below the scale coverings of the adult females. When the eggs hatch, the nymphs crawl from underneath their mother’s scale and move a short distance to their own feeding site. The newly emerged nymphs are also called crawlers. At their new location, the nymphs insert their slender stylets (mouthparts) into the plant and begin sucking sap. The covering or shell develops soon after feeding begins. Scale insects remain at these feeding sites the rest of their lives.
A small scale infestation causes little harm to healthy houseplants. However, a heavy scale infestation may result in poor, stunted growth. In severe cases, death of infested plants is possible.
Scale insects are difficult to control. Systemic insecticides are generally ineffective. The shell-like covering protects the scale from contact insecticides. The only time scale insects are vulnerable to contact insecticides is during the crawler stage. Since scale insects on houseplants don’t reproduce at a specific time, scale-infested plants will need to be sprayed with insecticidal soap or other houseplant insecticide every 7 to 10 days until the infestation is eliminated. Small infestations can be controlled by individually scraping off the scales or by dabbing each scale with an alcohol-soaked cotton swab. It’s often best to discard houseplants that are heavily infested with scale as control is nearly impossible and the insects could spread to other houseplants.
Learn more about houseplant pests in this article: Diagnosing Houseplant Problems Caused by Insect Pests.