Managing Houseplant Pests Fact Sheet No. 5.595 Insect Series|Home and Garden by W.S. Cranshaw* Houseplants are susceptible to attack by it with petroleum jelly or some other sticky Quick Facts many insects and mite pests. Some of these material. However, trapping alone will not houseplant pests can cause extensive damage entirely eliminate problems because much of • Many houseplant insect to the appearance and health of the plant the population, including the younger stages, problems are introduced by while others are simply a nuisance. Plants remain on or about the plants. infested plants. that are not vigorously growing and/or are Sanitation. Seriously infested plants are under stress may be particularly susceptible often best discarded because they usually • Carefully check plants before to insect and mite injuries. require lengthy and extraordinary efforts to purchasing and quarantine Infestations of scale insects (mealybugs control the pests. They may also serve as a them in a separate area and whiteflies) are almost always established source for infesting other plants. You can use for a few weeks to avoid from infested plants recently purchased or periodic “host-free” intervals to cause insects introducing new pest received as gifts. As a precaution, all new that survive for short periods without feeding problems. plants should not be placed with existing to die out. houseplants for at least three weeks. A careful Biological controls. Under certain • Changes in cultural practices inspection at the end of this time helps conditions, natural enemies of houseplant can help control many determine the presence or absence of pests. pests are effective in reducing the problem to houseplant insects, such as acceptable levels. However, they are relatively fungus gnats. difficult to acquire and are usually available • Several insecticides Methods Used to Control only through specialty suppliers. See Table are available to control Houseplant Pests 1 for a list of several biological controls for houseplant pests. For some Syringing plants. Many household pests associated with houseplants. plant pests can be controlled, at least in Alcohol. Sprays of alcohol, or alcohol pests, biological controls part, by washing the plant periodically with dabbed onto insects, is well known as a useful also exist. a vigorous jet of water. This is particularly control of mealybugs. However, using alcohol effective for spider mites and aphids, which on plants may cause injuries such as leaf are most readily dislodged. burn. Carefully test a small part of the plant if Cultural changes. Watering affects you attempt to use this method. houseplant pests in a couple of different ways. Insecticidal soaps. Insecticidal soaps Excessively moist soil favors the development (potassium salts of fatty acids) are one of of problems with fungus gnats. However, the most commonly available houseplant plants placed in very hot, dry sites are prone insecticides. These are used as dilute sprays to problems with spider mites. (one to three percent concentration) and can Handpicking. Larger houseplant insects help control many houseplant insects and can be controlled by handpicking. This spider mites. Many liquid hand soaps and is especially useful for scale insects and dishwashing detergents also have insecticidal mealybugs. Regularly using small, hand-held effects, although there is potential for plant vacuums assist in controlling whiteflies. injury with such treatments. See fact sheet Trapping. Yellow sticky traps can be 5.547, Insect Control: Soaps and Detergents for useful to reduce the number of insect more information. pests that fly – whiteflies, winged aphids, Horticultural oils. Diluted sprays of oils and fungus gnats. These traps are sold (petroleum distillates, mineral oils) are some commercially or you can easily make them by of the most useful insecticides for houseplant © Colorado State University cutting bright yellow cardboard and covering pests, capable of controlling scales, young Extension. 9/01. Revised 6/13. whiteflies and spider mites. These are highly www.ext.colostate.edu refined oils that primarily act by smothering. *Colorado State University Extension entomologist and professor, bioagricultural sciences and pest See fact sheet 5.569, Insect Control: management. 6/2013 Horticultural Oils for more information. Table 1. Summary of biological controls for insects and mites affecting houseplants and interiorscapes. Species Pest(s) controlled Comments Predator mites Spider mites Several species of predator mites are available that feed on spider mites. Check with a supplier as to the species best adapted to the environment of the plantings. Predator mites are quite perishable. Whitefly parasites Whiteflies Can effectively manage greenhouse whitefly if temperatures are (Encarsia formosa, maintained at an average of at least 72 to 75 degrees F. Inefficient at lower Eretmocerus californicus) temperatures. Available through several mail order suppliers. Mealybug destroyer Some mealybugs A species of lady beetle that feeds solely on young and eggs of mealybugs. (Cryptolaemus This species has been used successfully in some indoor plantings but montrouzieri) requires fairly high mealybug populations to maintain. Most effective in warm temperature settings. Available through several mail order suppliers. Mealybug parasite Mealybugs Has provided control of mealybugs in atrium settings. Available through (Leptomastix dactylopii) some mail order suppliers. Aphid predator midge Aphids Larvae are predators of aphids. These have been most effective at higher (Aphidoletes aphidimyza) temperatures. During winter supplemental lighting must be provided to maintain a minimum of 12 hours daylight or they become dormant. Available through some mail order catalogs. Green lacewings Aphids, primarily A general predator that feeds on a wide variety of insects and may help suppress mealybugs, scales and spider mites. Widely available from garden catalogs, often as eggs. Neem. Some houseplant insecticides Bacillus thuringiensis var. israelensis nymphs are scale-like in shape, translucent are derived from seed extracts of the (H-14 strain). A naturally occurring color, and fairly immobile. Feeding on the neem plant, a commonly grown tree in soil bacteria, Bacillus thuringiensis, has leaf undersides, whitefly nymphs are often many tropical areas. Neem seed contains the ability to control many insects. It is a inconspicuous and easily overlooked. After materials that disrupt insect growth and is commonly used microbial insecticide. See feeding for two to four weeks, whitefly useful for control on developing whiteflies fact sheet 5.556, Bacillus thuringiensis for and some other insects. Neem seed also more information. Different strains of this contains oils that may be used in a manner bacteria occur which may have different similar to other horticultural oils and is sold effects on insects. For example, one strain in products labelled as containing “clarified (“kurstaki”) is commonly sold to control hydrophobic extracts of neem seed.” caterpillars on vegetables and ornamental Pyrethrins and pyrethroid plants. Another strain, “israelensis” or insecticides. Pyrethins are a common “H-14,” can control certain larvae of gnats, ingredient in many houseplant and blackflies, and mosquitoes. It is sold under garden insecticides. They are a natural the trade names Gnatrol and Knock- product derived from flowers of a certain Out Gnats to control fungus gnat larvae (pyrethrum) daisy. Pyrethrins are fast in houseplants. Figure 1: Greenhouse whitefly adult and acting, have a very short persistence (a few nymphs. hours), and low toxicity. Several “synthetic pyrethrins,” better Common Houseplant known as pyrethroids, are also commonly Pests used. These are synthetically manufactured Greenhouse Whitefly insecticides based on the chemistry of Greenhouse whitefly (Trialeurodes the natural pyrethrins. Some of these vaporariorum) is a common pest of pyrethroids, such as resmethrin and several houseplants such as poinsettia, sumithrin, are also fast acting and have a ivy, Hibiscus, and Lantana. Greenhouse- short persistence like the natural product. grown vegetables, such as tomatoes and However, other pyrethroids, such as cucumbers, are also frequently infested. permethrin, cyfluthrin, and bifenthrin, may Damage is caused from the insects sucking persist in active form on foliage for several sap from the plant. Heavily infested plants days. Pyrethroids may have differences in may drop leaves prematurely and have their ability to control houseplant pests, reduced vigor. During feeding, whiteflies such as bifenthrin, which is much more also excrete sticky honeydew that detracts effective than other pyrethroids against from the appearance of the plant. spider mites. Winged adults are the stage most Systemic insecticides. Some commonly seen. They are somewhat insecticides, known as “systemic gnat-like and covered with fine white wax. insecticides” have the ability to be absorbed Adults lay eggs on the leaves. These eggs by plants. Those used on houseplants are hatch in three to seven days to produce the sold as granules or as stakes. They are immature nymph stage. Most feeding injury applied to the soil for the roots to absorb. to the plant occurs by the nymphs. Whitefly Figure 2: Greenhouse whitefly adults. Insecticides containing pyrethrins (Leptomastix dactylopii). However these or related insecticides (tetramethrin, are expensive and difficult to use effectively resmethrin, sumithrin) are