Daniel Gill, Merrill, Thomas A. | 11/22/2005 4:10:06 AM
By Dan Gill
LSU AgCenter Horticulturist
This time of the year, when we have brought many of our container plants – particularly the tropicals – inside for the winter, we need to be on the lookout for pest problems.
When they happen, indoor pest infestations can be devastating if not dealt with promptly, effectively and safely.
Indoor outbreaks of insect pests can spread rapidly and cause tremendous damage because of the indoor environment. There is no rain to wash off insects, the temperatures are never too high or too low, and there are no natural predators inside to help control insect populations once they get started.
In addition, insects spread rapidly because we often group houseplants together in well-lit locations close to windows or glass doors. We also do our share of spreading pests around by handling infested plants and then handling healthy plants.
Careful and regular inspection of your plants indoors 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 that are usually less than 1/8-inch long, distinctly segmented and covered with a powdery or cottony waxy secretion. They are sucking insects, feeding on the plant’s sap much the way mosquitoes feed on our blood. 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 be and feel sticky, and the new growth may appear weak and deformed. Many older leaves will begin to turn yellow and drop off.
Scales are related to mealybugs and 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 notice, they have settled in one place and no longer move.
You may notice the symptoms of scale before you actually see them. Like mealybugs (and many other sucking insects), scale infested plants will often 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 scale) on surfaces under the plant. If the population of scale insects on a plant passes the plant’s tolerance, the plant will begin to lose vigor, and leaves will yellow and drop off.
Spider mites are very tiny (most are not even visible to the naked eye), and the damage they cause is initially very subtle. This makes early detection difficult, so populations generally are out of control and damage is extensive before the indoor gardener sees there is a problem.
Initial damage from spider mites to the foliage of a plant causes it to appear dull, faded and unhealthy. As damage increases, new growth may be faded, stunted and deformed, and older leaves may become very faded, develop brown edges and begin to drop off. High populations of red spider mites will form fine webbing on the plant.
Virtually every plant we grow indoors is susceptible to one or more of these pests. When a pest problem is detected, prompt action is called for. First, isolate the plant or plants infested. All three of these pests are contagious. So always wash your hands after working with an infested plant, especially if you are about to handle healthy plants.
Remember there are no natural controls indoors, so if the pest is to be eradicated, you’re going to have to do the job yourself. If you would prefer not to use a pesticide, physical control is worth a try but requires effort and persistence. Spraying the plant every day with a strong stream of water (get under the leaves especially well) usually will get rid of spider mites. Continue spraying for at least a week.
You can try removing mealybugs with a cotton swab dipped in rubbing alcohol, but the process is tedious, must be done repeatedly and often fails to do a complete job of control.
On small plants you can try to control scale by dislodging them individually with your thumbnail (yes, this is tedious), then wiping down the leaves with a damp cloth. Repeat once a week as long as necessary.
If you decide to use pesticides, choose materials that are labeled appropriately for use on plants indoors and are safe to use on the plant you intend to spray.
Mealybugs, scales and mites are all controlled by oil sprays, which kill pests by suffocation and are very low in toxicity. SunSpray Ultra-Fine Oil has a label for use indoors.
Many insecticidal soaps and products containing pyrethrin also are approved (labeled) for indoor use and are excellent for mites and good on mealybugs but not very effective on adult scale. You can often find these in products premixed and ready to spray.
In all cases, use pesticides cautiously and follow label directions precisely. And remember, whatever product you choose, several applications will be necessary for complete control in most situations.
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.