Insect damage to houseplants often occurs during the winter months because the natural enemies that keep insects and mites outside either do not survive to move indoors or do not have time to bring plants indoors in the fall.
Insects can also be brought onto newly purchased plants or gift plants that are infested. Many of these pests can cause significant damage and spread to healthy plants in an area.
To prevent widespread infestations, consider different control strategies using minimally toxic methods. These options include mechanical, physical, cultural and chemical controls. Plants that grow vigorously under ideal conditions are less susceptible to pests.
Careful observation is important when bringing in plants from outside or adding newly purchased plants to your indoor garden. Look under the leaves and at the base of the stem for creeping or anything that looks unusual. Check for damage, rot and honeydew and continue to monitor plants regularly. Consider separating newly purchased plants and infected plants. Remove heavily infected plants.
Three common pests that affect houseplants are mealybugs, scale insects, and spider mites. All three suckers secrete plant sap through their mouths and can cause similar symptoms such as plant stunting, leaf drop, yellowing leaves, brown or deformed leaves, discoloration, wilting or spotting.
White bow tie
Aphids are segmented, soft-bodied insects found on leaves, stems and roots. These slow-moving, white, cotton-like insects are covered in a waxy substance that threads around their bodies.
Adult females are 1/20 to 1/5 inch long and can lay hundreds of eggs that hatch over several days. Newly hatched caterpillars are more agile and have no wax. You can infect new plants at this stage. When they start feeding, they secrete a layer of wax and a sweet, dark liquid called honey. Honeysuckle can cause sooty mold and blacken infected plants.
Aphids are commonly found in colonies on the undersides of leaves, along veins and at the base of pods. Common host plants include Chinese cypress, coleus, jade, poinsettia, schefflera and palm. Plants grown indoors or in greenhouses are susceptible to infection because mild temperatures allow populations to grow year-round.
Scale insects
Two different groups of scale insects, soft scale and shell scale, are common pests of houseplants. Some of these disc-shaped insects look like oval shields or fish scales, while others look like balls of colored wax.
Its color ranges from brown to yellow-green with some brown spots, and it is difficult to spot as it blends in with the host's bark or leaves. They range in size from 1/16 to 1/2 inch and are found on stems, under leaves, and along the center of leaves. They are found on many plants, but indoors they often cause problems for figs, shefflera, English ivy and citrus.
Adult female scales are legless and covered in a waxy coating that helps protect them. They lay eggs under their bodies, which hatch into mobile caterpillars. This stage can infect new plants either by creeping or by transmission from one plant to another. Soft gambits shed honeydew, which can cause sooty mold.
Spider mite
Spider mites are even smaller than the previous two (1/50 inch) and are not insects, but arachnids like spiders and mites. They appear as small reddish or pale green spots on the underside of leaves. Heavy infestations result in spots on the leaves and stems.
To find spider mites, place a piece of white paper under a leaf, touch the leaf, and use a hand lens to check for looseness. Rats move like dots on paper.
Spider mites can complete their life cycle in one to two weeks, depending on temperature. They develop faster in hot and dry climates and more slowly in cold and wet climates. Adult females live 2-4 weeks and lay up to five eggs per day which hatch in about 3 days. A female can lay hundreds of eggs in her lifetime. Newly hatched nymphs and adults feed on plant sap. Common houseplants include palms, English ivy, dracaena, figs, hibiscus, Norfolk Island pine and shefflera.
Just a sight
To combat mealybugs and dandruff, use a cotton swab dipped in 70% alcohol to identify individual insects. This will dissolve the wax around the insect and kill it. Avoid getting alcohol on plant leaves to avoid injury. Use a plastic cloth or your fingernail to knock off the tick. A dry toothbrush or cotton swab will also loosen it. Repeat every few weeks.
For heavy infestations, use an insecticidal soap labeled for houseplants. Follow all label directions and make sure the label contains plants and insects. Insecticidal soaps and horticultural oils labeled for indoor use will only kill the insects they come in contact with during application and must be reapplied several times.
Spray the plant with water or wipe the leaves with a damp sponge or paper towel to remove insects and honeydew. Use a slow release fertilizer that is not high in nitrogen to prevent excessive growth, mealybug production and an ideal environment for scab.
If possible, keep plants outside so natural predators such as ladybugs, lacewings and parasitic wasps or flies can provide biological control.
Reduce plant stress and improve plant environment with proper watering, regular washing and proper humidity levels. Plants grown under optimal conditions are the best protection against pest attacks.
Mary Clark is Penn State's Master Gardener in Beaver County.
This article originally appeared in the Beaver County Times;
