Richard Bogren, Gill, Daniel J.
For Release On 11/27/15
By Dan Gill
LSU AgCenter Horticulturist
Insect outbreaks on indoor plants can be disastrous. Indoors, insect pests can reproduce rapidly and cause tremendous damage because of the indoor environment. There is no rain to wash them off the plants, the temperatures are never too warm or too cold, and no natural predators live inside to help control insect populations once they get started.
Insects spread rapidly indoors because we often group houseplants together in well-lit locations close to windows or glass doors. With plants in such close proximity, insects have no problem moving from plant to plant. We also do our share of spreading pests around by handling infested plants and then handling healthy plants.
Close and regular inspection of your indoor plants is the best defense against pest outbreaks. Three of the most common pests that occur indoors are mealybugs, scales and spider mites. If you can identify these problems in the early stages, you can reduce the amount of damage that occurs and prevent the spread to plants that are not yet infested.
Mealybugs are small, oval, soft-bodied insects usually less than one-eighth inch long, distinctly segmented and usually covered with a white, powdery or cottony wax secretion. They are sucking insects and don’t move around much on the plants, tending to clump together. Look for cottony masses in the growing points of plants, in their crowns, under their leaves and where the leaves join the stem of the plant.
Plants heavily infested with mealybugs will appear unhealthy. The leaves of the plant may have a shiny appearance and feel sticky, and the new grow may appear weak and deformed. Many older leaves will begin to turn yellow and drop off.
Scales are also sucking insects. They are covered with a dome-shaped, waxy coating that is most often white, tan or brown, depending on the type of scale. Once they are large enough to be noticed, they do not move. This, along with their waxy covering, makes it difficult to notice them. And once you do see the strange bumps or dots on the plant, you would never think that they are insects.
If the population of scale insects on the plant exceeds the plant’s tolerance, the plant will begin to lose vigor and leaves will yellow and drop off.
Like mealybugs, as scale insects feed on the sap of the plant, they excrete tiny droplets of a sugary liquid called the honeydew. Scale- and mealybug-infested plants will often have shiny, sticky leaves. Even the floor or table below the plant becomes sticky. This is the result of the accumulation of honeydew. You may even see a black fungus called sooty mold growing on the accumulations of honeydew. This can be another sign a plant is infested.
Spider mites are very tiny (most are not visible to the naked eye), and the damage they cause is at first very subtle. Initial damage to the foliage causes it to appear dull, faded and unhealthy. As damage increases, new growth may be stunted and deformed and older leaves may become very faded, develop brown edges and begin to drop off. High populations of mites will form webbing where the leaves join the main stem.
These three pests attack a tremendous variety of indoor plants. Virtually every plant we grow indoors is susceptible to one or more of them. When a pest problem is detected, prompt action is called for. First, isolate the infested plant or plants. All three of these pests are contagious. Always wash your hands after working with an infested plant, especially if you are about to handle healthy plants.
If you decide to use pesticides, you must choose materials that are labeled appropriate for use on plants indoors and are safe to use on the plant you intend to spray. Do not use sprays that are only meant to be used outside or those for controlling indoor house pests such as roaches or ants.
Mealybugs, scales and mites are all controlled by oil sprays, which kill pests by suffocation and are relatively low in toxicity. Look for light horticultural oils that have a label for indoor use.
Several brands of insecticidal soaps and products containing pyrethrin also have labels for indoor use and are excellent for mites and good on mealybugs but not very effective on adult scale.
Use pesticides cautiously and follow label directions precisely. Because spraying is so messy, spray plants outside whenever it is practical. Whichever product you choose, several applications are necessary for complete control in most situations. Be persistent and apply follow-up applications as needed to ensure compete control.
As many of us are bringing tender containerized plants indoors for the winter, make sure you check them very carefully and take any pest control steps necessary before you bring them inside.