Common Houseplant Pests

Scales and mealybugs are common insect pests on houseplants. They are a real nuisance and have an interesting life cycle. The stage that hatches from an egg is called the nymph. Scale and mealybug nymphs are tiny, 1/32 1/16 inches long, and they start out with legs and antennae. They molt in a week or so, shedding their legs and antennae and park themselves in one spot by inserting their mouth like a siphon into the host plant. They will spend their lives drinking the plants fluids through this straw-like mouthpart. Mealybugs begin to form their protective covering after their first molt. It is a sticky, waxy, cottony-like substance that protects them from predators and the elements. Scale insects form a similar protective covering, but theirs is more like a shell, usually smooth in appearance. Often scale insects look like part of the plant and the best way to tell if the bumps you see are indeed scales is to scrape them gently with a fingernail or dull knife. If the shell comes off, you know its a scale. If you end up scraping off part of the plant tissue, then it was some sort of warty bump or natural part of the plant. Eventually, the males will mature and form wings so they can fly short distances to find females, but the female scales never move after their first molt. Mealybugs move very slowly, if at all. During that first stage, the nymphs are called crawlers, and this is when they are the most vulnerable. Soon they form the protective covering that protects them from predators and insecticides. We've been getting calls lately from people whose plants are infested with scales or mealybugs. Often the first way you notice you have a problem is you see shiny patches on the floor beneath your plant or on the lower leaves of the plant. Some of the most frequently infested houseplants are the smooth-leaved plants such as schefflera, weeping fig, citrus and spider plant. When you see these shiny, sticky patches look up, and chances are youll find scales or mealybugs. These insects drink the plant fluids, which they then excrete in the form of a sticky, sweet honeydew which drips onto any surface below. Sometimes you will see black fuzz growing on these sticky patches, but that is no problem. It is sooty mold that feeds on the sugar content of the honeydew. Once the honeydew is gone, the sooty mold will be gone, too. Both scales and mealybugs are very difficult to completely control. Their protective coverings help them resist gentle washings and, even if you resort to using insecticides, they are quite resistant to them. When an infestation is severe, I usually ask the person how valuable is the plant. Often the best solution is to start over, either with a brand new plant, or with cuttings taken from the original plant which are carefully cleaned of any lingering pests. I realize this may not be the easy answer people are hoping for, but it is the most practical.

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