Those houseplants you've kept outside all summer may be harboring unwanted guests.
"When bringing plants inside for the winter, it's important to check them for insects and other pests," says Dr. J. Robert Nuss, professor of ornamental horticulture in Penn State's College of Agricultural Sciences. "Even one or two insects can be the start of an infestation."
Pests to look for are aphids, mealybugs, spider mites, white flies and scale.
Aphids are small, black or green crawling insects that live in thick colonies along the soft parts of stems, sometimes covering them entirely. They excrete a sweet liquid called honeydew, which often attracts ants. "Aphids are quite destructive," says Nuss. "They cause distorted and curled leaves, malformed flowers and hardened buds."
Mealybugs are about the same size as aphids but are white and fuzzy. Masses of them, resembling pieces of cotton, nestle and lay eggs where leaves and branches attach to stalks. Mealybugs can stunt and kill plants by depleting their fluids.
White flies also are small and white, but unlike mealybugs, will take flight if you shake the plant. "You'll never find just one white fly on a plant," says Nuss. "They come in quantities and can spread to all the plants in your house."
Spider mites are miniscule but very destructive. An infested plant will have yellow-speckled leaves and may be covered with tentlike webs. "The mites look like grains of cayenne pepper," says Nuss. "They're easy to spot if you hold a piece of white paper under the plant and shake the leaves so the mites drop onto the paper."
Scale appears as blister-like areas on stems and the undersides of leaves. These areas can be circular, oyster-shell-shaped or rectangular and are colored white, brown, gray or black. Scale also produces honeydew, which may drip from the leaves. "Scale seriously stunts growth," says Nuss. "If not treated, it can kill the plant and spread to other plants."
"With a small infestation, you may be able to wipe the pests off with a Q-Tip dipped in alcohol," says Nuss. "Rinsing the plant under a gentle stream of water for a few minutes can wash away insects and eggs. Keep checking the plant for a recurring infestation during the next couple of weeks."
It's also important to gently dig around the roots and look for pests in the soil, such as sow bugs, millipedes and slugs. You can remove most of these by hand, or you may want to rinse the soil off with a garden hose and repot the plant in new soil.
Serious, persistent infestations can be treated with an insecticidal soap spray or a multipurpose insecticide containing a miticide. Both are available from gardening centers. "Be careful to follow the directions on the label exactly," says Nuss. "Excess spray can be toxic to the plant. And if you spray too closely to the leaves, the aerosol propellant can freeze them."
After spraying, keep the plant in a large plastic bag for a few hours to contain and concentrate the spray, then isolate it for about two weeks or until you're sure it's pest-free. "It also is a good idea to follow all these precautions if you've bought a plant or received one as a gift," says Nuss. "Even well-cared-for nursery plants can harbor pests."
Fall also is the time to repot plants that have been outdoors all summer. Turn the plant upside down and tap the bottom of the pot while supporting the plant. The roots and soil probably will come out in one piece. If the roots are crowded into the shape of the pot, it's time to remove the old soil and move the plant to a pot one size larger.
If the plant has grown excessively, you may want to trim it to an appropriate indoor size. "Trimming can stimulate more growth, so you might need to do it again later," says Nuss.
When the plant is repotted, trimmed and pest free, place it inside where it will get at least a few hours of full sun every day, and rotate it once a week so it will grow straight. Fertilize moderately and water only when the soil is completely dry. "It's best even to let the plant wilt slightly before watering," says Nuss. "Overwatering quickly can kill plants."
Is setting your plants outside worth all the hassle? "The advantages are great," says Nuss. "Sunlight, rain and warm weather produce a flush of healthy growth, and the pests usually are easy to get rid of. Overall, it's worth it."
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