For Release On Or After 11/19/10
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 environment. There is no rain to wash them away; temperatures are never too warm or too cold; no natural predators lurk inside to help control insect populations once they get started.
Insects spread rapidly 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 one to another. We also do our share of spreading pests around by handling infested plants and then handling healthy ones.
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 not yet infested.
Mealybugs are small, oval, soft-bodied insects usually less than 1/8 inch long. They’re distinctly segmented and usually covered with a 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.
Plants heavily infested with mealybugs will appear unhealthy. The leaves may have a shiny appearance and feel sticky, and new growth may appear weak and deformed. Many older leaves will begin to turn yellow and drop off.
Scales also are sucking insects. They are covered with a dome-shaped waxy coating that’s most often white, tan or brown, depending on the type of scale. Once they are large enough to notice, scales are immobile and don’t move. This, along with their waxy covering, makes it difficult to notice them. And once you see the strange bumps or dots on the plant, you would never think they’re insects. If the scale population is greater than the plant can tolerate, the plant will begin to lose vigor, and leaves will turn yellow and drop off.
Scale- and mealybug-infested plants often will have shiny, sticky leaves. Even the floor or table the plant sits on may become sticky. This is the result of the accumulation of honeydew – a sweet, sticky excretion of the insects – on surfaces under the plant.
Spider mites are very tiny. Most are not even visible to the naked eye, and the damage they cause is initially 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 build webs 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 you detect a pest problem, prompt action is called for. First, isolate the infested plant or plants, because all of these pests can move to other plants. Always wash your hands after working with an infested plant, especially if you’re about to handle healthy plants.
If you decide to use pesticides, you must choose materials that are labeled appropriate for use indoors and are safe to use on the plant you intend to spray. Do not use sprays that are meant to be used outside or those for controlling other indoor pests such as roaches or ants.
Mealybugs, scales and mites are all controlled by oil sprays, which kill them by suffocation and are relatively low in toxicity. Look for light horticultural oils that have a label for use indoors. Many insecticidal soaps and products containing pyrethrin also have labels for indoor use and are excellent for mites, 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’s practical. Whatever product you choose, several applications are necessary for complete control in most situations.
As many of us get ready to bring tender containerized plants indoors for the winter, make sure you check them over very carefully and take any pest control steps necessary before you bring them inside.
Rick Bogren