If your houseplants have been given all the food, water, and sun they need and they still seem to lack vigor, you may want to inspect them closely for insect pests. Insects and mites can appear on houseplants at any time of the year and they are not always easy to see. They often arrive on recently purchased plants or on plants that have been received as gifts. Fortunately, most houseplant pests can be easily treated with a solution of soap and water, rubbing alcohol, or with sticky traps.
Commonly greenish-white or black in color, aphids are easy to detect because they tend to cluster in the open. They will attack all types of indoor (and outdoor) plants, but seem especially fond of ornamental peppers, hibiscus, chrysanthemums, and herbs. They stunt plants' growth and leave them looking distorted by sucking sap from their stems and leaves. Attack aphids with a wash of warm, soapy water followed by a clear rinse as recommended for spider mites. Successive generations may hatch, so be prepared to re-treat the plant to achieve final victory.
These gnat-like pests commonly attack houseplants such as Poinsettia, Ivy, Hibiscus, and Lantana (vegetables such as cucumbers and tomatoes are also frequently infested). Like many sap-sucking insects, as they feed they excrete a sticky honeydew that detracts from the appearance of the plant and invites other problems. Although the winged-adults are the stage most commonly seen, it's the immature nymph stage that causes the most injuries to plants. To interrupt the life-cycle, use yellow sticky cards stuck into the soil to trap the adults. These are available at most garden centers, or you can make your own using bright yellow paper smeared with petroleum jelly. On small plants, adults can also be extracted using a hand-held vacuum.
If you see white, cottony blobs on any part of a plant-especially on the undersides of the leaves and stems-you probably have a mealybug problem. These pests often go unnoticed because they gravitate to parts of the plant that are not exposed to the sun. To get rid of them, dab each bug with a cotton swab dipped in rubbing alcohol. (Avoid touching the plant's leaves with alcohol as it may cause burns.) Afterwards, rinse the leaves with tepid, un-softened water. Be persistent in your efforts to eradicate them. This pest has a track record of winning when gardeners give up too easily!
These tiny bugs (usually red, white, or spotted tan in color) feed underneath the leaves, spinning fine webs along the veins of the leaves and leaving the plant with a gray webby look and anemic foliage. Original infestations are most likely to occur from plants that have been kept outdoors and then moved inside. Some of their favorite hosts include ivies, dracaenas, figs, hibiscus, Norfolk Island pine, and scheffleras. Heavily infested plants should be tossed out as they are difficult to control in large numbers. If you are lucky enough to notice a mite problem before your plant has sustained significant damage, take it outside, lay it on its side, and blast the undersides of the leaves with a spray from the hose. If temperatures make taking the plant outside impossible, fill a pan with lukewarm water and mild dish soap. Cover the top of the pot with aluminum foil to hold in the dirt, then turn the plant over and swish the foliage through the suds. Rinse well with clear water. Several weekly baths may be necessary to get rid of these guys completely. Spider mites prefer a dry environment, so mist foliage daily to discourage resettlement.
Although this tiny insect pest causes little to no damage to your houseplants, it is a giant sized nuisance. Fungus gnats are small, dark-colored flies that can often been seen jumping or flying near the soil's surface. They are native insects and are often transported indoors via garden soil or unsterilized potting soils. Because these insects develop in the soil, all houseplants are considered fair game. The larvae prefer moist soil because they prefer to feed on fungi, decaying organic matter, and the plant's root hairs (which can cause some loss of vigor). One way to suppress their numbers is to remove any decaying plant matter from around the base of the plant and let the surface of the soil dry out between watering. Adult gnats can be trapped with yellow sticky cards.
Another common sucking insect, scale is highly attracted to the likes of ferns, ficus, ivies and citrus plants. The young scale is small, crawly, and hard to detect until it digs into the stems of leaf veins and grows hard, brown scales. No wash or water spray will dislodge these small barnacles, and their hard protective armor can be difficult to penetrate with alcohol. One of the most effective ways to remove them is to dislodge them using a soft toothbrush or wet cloth.
By Ellen Brown