Pest and Disease Problems of Indoor Plants

Houseplant choices range from tough and resilient plants to those that are very specific about their cultural needs, requiring perfect growing conditions to thrive. Choose the right plant for your indoor environment, making sure new purchases are healthy and pest-free. Ideally, new plants, as well as those brought inside for the winter, should be isolated from other houseplants for about three weeks.

Monitoring is key in caring for plants and dealing with any issues that crop up. When you are caring for your plants, take a good look at their foliage, stems, and soil. Be on the lookout for signs of pests and disease.

Pests Commonly Found on Houseplants

Aphids — small, soft-bodied insects that feed on the branch tips and underside of leaves. They cause distorted new growth on plants such as ivy, herbs, and hibiscus.

Mealybugs — appear white and "cottony" and are found on stems, leaves, and roots of plants. They commonly occur on cacti and succulents, coleus, poinsettia, African violets, and gardenia. Feeding damage causes stunted growth and premature leaf drop.

Soft scales — only crawlers are mobile; once attached to a feeding spot on the plant, they secrete a waxy coating over their bodies, which cannot be removed.  Adult scales have oval/round, green or brown shells. They attach to the leaves and stems of plants, including ficus, citrus, ferns, and ivy.

Whiteflies — small, white, gnat-like insects which swarm when disturbed. Poinsettia, ivy, and hibiscus are favorites of whitefly. Impacted plants display yellowing, reduced vigor, and leaf drop.

Thrips — extremely small (1/16 inch) insects, nymphs feed on flowers and the undersurface of leaf tissue. They cause streaking and distortion of flowers and foliage, and buds often fail to open.  Common problem on greenhouse-grown primrose.

Spider mites — tiny arachnids (not insects) which thrive in hot, dry conditions. Dracaena, figs, hibiscus, ivy, Norfolk pine, and scheffleras can be affected by spider mites. They feed on the undersides of leaves and create stippling, gray/bronze discoloration, premature leaf drop, and fine webbing.

Fungus gnats — Adults (1/8 inch) cause no damage, but are a nuisance swarming over soil in pot.  White larvae feed on organic matter and roots, reducing vigor of plants.

You may not see the insects afflicting your houseplants, but "honeydew," a clear sticky excrement of the insect is often seen. Aphids, whitefly, mealy bugs, and scale secrete honeydew when feeding.  Honeydew is shiny and sticky and is a medium for sooty mold growth, which will inhibit photosynthesis. 

Control methods include handpicking pests, rinsing both upper and lower leaf surfaces with warm water, or removing pests with alcohol-dipped cotton swabs in difficult-to-reach areas. For heavy infestations, prune infected parts or apply contact sprays of insecticidal soap or horticultural oil. Follow label directions. Be sure to apply any controls to the undersides of leaves to destroy insects that commonly feed in that area.

Clean soil and debris from pruners after every use. Disinfect pruners with a 10% bleach solution or full-strength isopropyl alcohol after using them on a plant with insects or disease. Affected plants should be isolated to prevent spreading to adjacent plants.

Diseases That Can Afflict Houseplants

Diseases are generally rare and harder to treat than insect infestations of houseplants.

Gray mold (Botrytis cinerea) — attacks older foliage and flowers, causes brown, wet spots on leaves or flowers. Dusty, gray spores are visible on infected tissue.

Leaf spot fungus — oval, brown/black spots, not limited by leaf veins, often with a yellow halo or purple band. Airborne spores spread to healthy leaves. Commonly affected plants include palms, yucca, orchids, prayer plant and dumbcane.

Powdery mildew — distortion and gray-white powdery coating on the leaves and stems of houseplants, especially African violets, succulents, and begonias.

Root rot — due to overwatering or damaged roots. While preventable, root rot is a soil-borne fungus that causes wilting and blackened, mushy roots.  Orchids, cyclamen, and succulents are especially susceptible.  

Disease prevention includes good sanitation of tools and pots. Provide ample air circulation for plants. Avoiding overcrowding, overwatering, and overpotting. Keep leaves dry. Remove leaves showing signs of fungal problems. Prune and discard any infected parts as soon as you detect a problem.  Discard severely affected plants.