Many houseplant problems such as yellowing leaves and stunted growth can be attributed to insect infestation. Houseplants are susceptible to attack by a number of insect species. Some of these houseplant pest species can cause extensive damage ranging from foliage and flower discoloration to stunted growth to more serious issues such as eventual plant death. Plants that are not well cared for or are under stress may fall prey to these common houseplant insects and be afflicted with these problems. Good plant health is the best defense.
Problems Caused by Mealy Bugs
The yellowing of foliage, loss of leaves or poor growth could be a sign of mealy bugs. Mealy bugs suck sap from plants, weakening the plant and leading to these problems. Mealy bugs are soft-bodied insects about 3/16 inch long. Their bodies are white as though dusted with flour. They are commonly found on the undersides of leaves, at the leaf joint and infesting the roots. Mealy bugs like coleus, cactus, lantana and poinsettia.
Problems Caused by Scale Insects
Drooping, yellowing leaves and stunted growth could be due to scale insects. Scale insects use needle-like mouth parts to feed on plant sap. To disguise themselves, they secrete a waxy shell-like covering that makes them look like brown or gray bumps. Round or oval, about 1/16 to 1/8 inch in diameter, scale insects can do a lot of damage. A sustained infestation can cause a severe die-back. Ficus, citrus, ferns and ivies often fall victim to scale insects.
Problems Caused by Spider Mites
Plants suffering from discoloration, defoliation and plant death may be the victims of spider mites. Spider mites are among the most serious houseplant pests. Spider mites damage plants by piercing leaf tissue with needlelike mouth parts, feeding on sap. Related to spiders and ticks, spider mites are not true insects. Spider mites are oval shaped, yellow or green and measure about 1/50 of an inch. Mites start feeding on leaf undersides and then move on from stem to stem and then to nearby plants. Watch out for mottled or pinprick yellow discolorations on the undersides of leaves, the earliest signs of a spider mite infestation. Spider mites can make their way into the house in summertime or on Christmas trees and greenery in the winter.
Problems Caused by Thrips
The presence of thrips is usually identified by the problems they cause. Light, irregular silvery areas developing on leaves are a sure sign of their presence. Streaked or distorted buds, flowers and petals are also signs of thrips. Thrips feed by scraping leaves or flowers and sucking the released fluid. These insects are very small (1/16 inch); the adults are usually tan or brown and the juveniles are white, yellow or orange. Thrips can transmit serious viral diseases to plants, such as tomato spotted wilt and impatiens necrotic spot. Carnations are a popular thrip meal.
Problems Caused by Whiteflies
Reduced plant vigor, yellowing and leaf loss could be evidence of whiteflies. Whiteflies feed on plant sap, piercing plant tissue and sucking the fluid. Whiteflies are related to scale insects and mealy bugs. White and mothlike in appearance, whiteflies are about 1/16 of an inch long, oval and found on the undersides of leaves. Poinsettia, ivy, hibiscus and lantana are whitefly favorites.