Daniel Gill, Merrill, Thomas A. | 10/27/2006 9:14:40 PM
By Dan Gill
LSU AgCenter Horticulturist
Insect outbreaks on indoor plants can be disastrous. So you need to keep a close watch on your houseplants to prevent major problems from developing.
Pests can reproduce rapidly and cause tremendous damage because of the indoor environment. There is no rain to wash off insects, the temperatures are never too warm or too cold, and there are no natural predators to help control insect populations once they get started.
Insects also 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 1/8 inch long, 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. Instead, they tend 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 plants may have a shiny appearance and feel sticky, and the 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 is most often white, tan or brown – depending on the type of scale. Once they are large enough to notice, they are immobile. Since they aren’t moving and they have the waxy coating, it’s 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 a plant passes the plant’s tolerance, the plant will begin to lose vigor and its leaves will yellow and drop off.
Scale-infested or mealbuy-infested plants often will have shiny, sticky leaves. Even the floor around a plant or a table it 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.
Turning to the other major pest, spider mites are very tiny – most are not even visible to the naked eye – and the damage that they cause initially is very subtle. That first damage to the foliage causes it to appear dull, faded and unhealthy.
As damage by spider mites increases, however, 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, so prompt action is called for when a pest problem is detected.
First, isolate the plant or plants that are infested. 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 meant to be used outside or those for controlling indoor house pests such as roaches or ants!
Mealybugs, scales and mites all can be 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 use indoors.
Many 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.
Whatever you choose, use pesticides cautiously and follow label directions precisely. In addition, since spraying is so messy, spray plants outside whenever it is practical and then bring them back inside. Also, keep in mind that several applications are necessary for complete control in most situations no matter what product you choose to use for insect control.
As many of us get ready to bring tender plants in containers indoors for the winter, make sure you check them over very carefully and take any pest control steps necessary before you bring them inside.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.