Watch for Houseplant Pests
by Don Janssen, Extension Educator
Though it may seem unlikely, especially if you never put any of your houseplants outdoors, houseplants can be attacked by pests.
Maybe they hitchhiked in on a recent acquisition; maybe they flew in through an open door or found their way in through a torn window screen. If you did put some plants outdoors during the warm months, the chances that you brought pests indoors with them are very good. Once inside, with no natural enemies or freezing temperatures to keep numbers in check, pest populations can really take off.
The most common pests of houseplants include spider mites, whiteflies, aphids, scale and mealybugs. These pests suck plant juices and cause stunting or twisted growth. Fungus gnat larvae and springtails may infest plant pots and injure roots. Thrips and even slugs may come indoors with plants and rasp tissue from flower petals and leaves.
If you find pests on one of your plants, the first thing to do is inspect the others. Then isolate infested plants to keep the infestation from spreading.
A thorough washing with a stream of water or an insecticidal soap solution is often enough to stop an infestation. With small plants, you can use foil or paper or a rag to hold the soil in the pot while you turn the container upside-down and swish the plant in a pail of lukewarm water for several minutes. Larger plants can be sprayed with a strong stream of water from a flexible hose hooked to the sink or laundry tub or, weather permitting, subjected to a gentle spray from a garden hose outdoors. Scale insects may require more vigorous treatment with a soapy cloth or soft toothbrush to dislodge them.
Chemical insecticides and miticides are another option. Some houseplants -- including African violets, gloxinia, orchids, begonias and some ferns -- are sensitive to some common products, however. Treating these sensitive plants is simply trading chemical injury for insect damage.
Check labels for warnings about sensitive plants. For these plants, a cotton swab dipped in rubbing alcohol is recommended. Try to keep the alcohol off the plant as much as possible, especially if you're treating plants that don't tolerate water on their leaves, such as African violets.
If you decide to try chemical insecticides, read labels carefully before you buy, make sure the plant you intend to treat and the pest are both listed on the label, and follow directions precisely when you treat your plants. Test the product on a small part of each plant before spraying or dipping the whole plant. If burned leaf tips or leaf edges appear within 48 hours, that plant and that product are not a good combination.
A severely infested plant may not be worth the investment of time and effort that it would require to control the outbreak. A severely damaged plant may take a long time to recover. In these instances, you might be doing yourself a favor to discard the plant and replace it.
Isolate treated plants and observe them closely for pest comebacks. Inspecting all houseplants regularly is a good habit to get into. Any pest problem is likely to be easier to contain and control if you catch it early.
(This resource was added November 2004 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement)
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