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 the most which limits their application primarily effective chemical controls for adult to large indoor plantings where using whiteflies. Horticultural oils, neem insecticides is not desirable or possible. insecticides, and insecticidal soaps may control nymphs on leaves. The systemic Spider Mites insecticide imidacloprid is highly effective The twospotted spider mite Tetranychus( against greenhouse whitefly. urticae) is one of the most common houseplant pests. Unlike whiteflies and Mealybugs mealybugs, the twospotted spider mite can Mealybugs are soft-bodied insects survive year-round outdoors in Colorado, that suck sap from plants. This weakens going dormant during the winter. Original the plant and causes leaves to shed. infestations of houseplants may arise from Mealybugs also excrete large amounts of plants kept outdoors, from mite migration sticky honeydew. Coleus, cactus, lantana, from outdoor plants, or by acquiring hoya, jade, and poinsettia are among the infested plants from a greenhouse. Once plants mealybugs prefer. Root-infesting established on a plant, spider mites can Figure 3: Citrus mealybugs on coleus. mealybugs are associated with African crawl short distances or be carried or blown violet and gardenias. to other plants. When full grown, most female Spider mites feed on plant sap, mealybugs produce a large amount of producing small wounds on the outer cottony material in order to lay hundreds plant cells which appear as white flecks. In of eggs. The eggs hatch within a few days. the beginning of a spider mite infestation, The newly emerged insects, known as these injuries occur as small patches on the crawlers, move about the plant. Oftentimes, leaf underside near the base of leaf veins. infestation of new plants occur during As damage progresses, the leaves have a Figure 4: Twospotted spider mite and eggs. this movement. Mealybugs mature in generalized “off” color that appear as a approximately two months. graying or bronzing. Spider mites also make Mealybugs may infest different areas webbing and in very high populations the of the plant. Although populations on webbing may be very visible. Often heavily foliage are most visible, most mealybugs infested leaves drop prematurely. Common infest roots and some are predominantly hosts include ivies, dracaenas, figs, hibiscus, associated with roots. Some species tend Norfolk Island pine, and scheffleras. to move to roots when growing conditions Spider mites have a short life cycle that are less favorable, but return in high can be completed in one to two weeks populations on stems and leaves when under favorable conditions. Approximately Figure 5: Spider mite webbing on Norfolk plants are actively growing. five eggs may be laid daily by a mature Island pine. Management. Swabbing individual female. Eggs hatch within a couple of mealybugs with alcohol is useful for days and the newly emerged nymphs feed nymphs change into an inactive “pupal” control. Dilute alcohol sprays (25 to 50 almost continuously. stage. This stage typically lasts one to two percent concentration) or insecticidal soaps Management. Spider mite control can weeks, before adults emerge. Adults may can also be used. However, before applying be difficult. Heavily infested plants should be active and lay eggs for two months if these treatments be sure to test a small area be disposed of whenever possible since conditions are favorable. because some plants may become injured. they serve as a source of new infestations. The greenhouse whitefly is a tropical Alcohol and soaps are strictly contact Fundamentally important is providing insect that is incapable of overwintering sprays with no residual action. Root- optimal growing conditions as spider outdoors in Colorado. Freezing feeding stages of mealybugs will be missed mite problems can be aggravated by a temperatures or a relatively short host-free with these treatments. poor environment. period eliminates greenhouse whitefly. Sprays of pyrethroid insecticides The most effective controls include Although most houseplant problems (tetramethrin, bifenthrin, permethrin) are washing and increasing humidity around originate from the purchase and movement usually effective for mealybug control. The the plant. Small plants can be repeatedly of infested plants, some whiteflies can soil-applied systemic insecticides disulfoton washed with a jet of water from a shower reproduce and infest new plantings during and imidacloprid can also be effective. or kitchen sprayer. This forces off the mites the warm summer months. Biological controls for mealybugs and eggs. If done over the course of several Management. Yellow sticky cards or include a species of ladybird beetle (the weeks, mite populations should be reduced tape can be used to trap adult whiteflies. “mealybug destroyer,” Cryptolaemus to low levels. On small plants, adult whiteflies can be montrouzeri) and a type of parasitic wasp eliminated by vacuuming. Twospotted spider mite is difficult leaf underside on plants such as citrus to control with pesticides. Horticultural and begonias. oils are probably the most effective spray. Management. Cyclamen mites can be Bifenthrin, found in many houseplant very difficult to control since they occur insecticide preparations, can also be deep within leaf folds and other protected effective for spider mite control. Insecticidal sites. Therefore, it is usually recommended soaps are marginally effective. that cyclamen mite-infested plants In large indoor plantings, using predator be discarded. mites may be considered. Several species Figure 9: Armored scales. (Photo by J. Capinera.) of predator mites are available and can Soft Scales be used successfully to manage mites on Several scales, particularly the brown greenhouse grown tomatoes, cucumbers, soft scale (Coccus hesperidum) and the and some ornamental plants. hemispherical scale (Saissetia coffeae) may attack houseplants. These occur on many Other Mites kinds of plants but problems are most Much less commonly found are the frequent on ficus, citrus, ferns, and ivies. cyclamen mite and the broad mite (Family Heavy infestations of soft scales result in Tarsonemidae). Both are extremely tiny and large amounts of sticky honeydew which do not make the webbing characteristic of can create serious nuisance problems. Figure 10: Chrysanthemum aphids. spider mites. Instead, the presence of these Sustained infestations can cause die back. mites is usually suspected from the plant The brown soft scale is found on both insecticide imidacloprid should be effective symptoms that they produce. Cyclamen twigs and leaves. Eggs hatch underneath for most soft scale infestations. mite often cause new growth to be stunted, the cover of the mother scale continuously twisted, and sometimes killed back. Leaves over a period of several weeks. The newly Armored Scales may also appear small, thick, and rough hatched “crawlers” have limited mobility Armored scales are much less common textured. African violet is the houseplant and usually move short distances in search than soft scales. Typical species are most often damaged by cyclamen mite. of feeding sites. After the scale crawlers generally round in shape, often with a Broad mite produces a bronzing of the settle to feed, they begin to produce the distinct central spot. Many cause spotting characteristic protective body covering around the feeding site. They can also cause and excrete honeydew as waste. The scales die back when abundant. Unlike soft scales, continue to grow over the next two to four they do not produce honeydew and, except months rarely moving in later stages. for a very brief period after egg hatch Management. Soft scales can be difficult (crawler stage), are immobile. Horticultural to control since their protective covering oils are the most effective treatment for largely prevents contact insecticides from armored scales. Systemic insecticides being effective. However, spray oils are the provide poor control. most effective treatments for scales. Alcohol Figure 6: Cyclamen mite damage to African and soap sprays may also provide some Aphids violet. (Photo by J. Baker.) control of scales, particularly crawler and Aphids develop as pests on several very young, poorly protected stages. types of houseplants including ornamental Where infestations are not widespread, peppers, hibiscus, chrysanthemums, and scales can be killed by rubbing or picking many garden plants and herbs. Aphids also them off. Fairly minor disturbance of the feed on plant sap and excrete large amounts settled scale can break its mouthparts, of sticky honeydew. In high populations causing it to starve. Scales killed in this they cause wilting and distortions of the manner, or by soaps or oils, may remain in new growth. place and appear similar to living scales. Aphids common on house plants Crawler stages are susceptible to include the green peach aphid, potato Figure 7: Brown soft scale. most houseplant insecticides. However, aphid, cotton/melon aphid, and insecticides must maintain coverage chrysanthemum aphid. Populations throughout an entire generation of the increase rapidly as generations can be insect (two to four months) to eliminate completed in two to three weeks. further infestation. Short persisting Management. Since aphids are exposed insecticides, such as pyrethrins and on the plant, periodic washing with resmethrin, need reapplying at least once water and contact sprays of insecticides is per week. Longer persisting treatments, effective. However, most aphids adapted such as bifenthrin and permethrin are to greenhouse culture, particularly the effective for scale control when used at green peach aphid, are highly resistant to Figure 8: Honeydew produced by brown soft longer intervals. Soil applied systemic scale. insecticides due to long-term exposure. Imidacloprid is particularly effective for Notes on using aphids. Insecticidal soaps and pyrethroid pesticides: insecticides may also be effective. Follow the cautions listed below when Biological controls for aphids have had modest success at best. Some aphids are using pesticides on houseplants to best controlled by a small predator midge, avoid exposure and plant injury. Cecidomyiia aphidomyza. Mass releases 1. Only use pesticides that are of green lacewing eggs, which hatch into specifically labeled for use on larvae that prey on aphids and many other houseplants. Most yard and garden insects, can also be effective. pesticides do not allow this use.

Thrips 2. If possible, take the plant outdoors Thrips are extremely minute insects, before spraying to minimize usually less than 1/16 inch when full- pesticide exposure within the grown. They have elongated bodies and home. Figure 11: Thrips and associated damage. are usually brown, although pale and dark forms can be common. Adults can fly and 3. When using aerosol sprays, do not their very small size allows them to easily apply closer than 18 inches to the penetrate most screening. plant or injury may occur from the Thrips are usually recognized by the spray. This precaution appears on damage they cause. Light, irregular silvery most label use directions. areas on the leaf surface develop around the feeding site. Tiny dark spots of excrement 4. Avoid treating plants that suffer appear at the feeding area. This feeding from environmental stresses may somewhat resemble spider mites, but such as temperature extremes or wounds produced by thrips are larger and drought to minimize potential plant more silvery. Thrips infesting buds and injury. developing flowers produce distortion and 5. If granules or plant stakes scarring of petals. Perhaps most important is the ability containing DiSyston are used, use of thrips to transmit certain virus diseases extra care when watering. Excess to plants. Tomato spotted wilt is a water may carry this insecticide as very serious disease, primarily affecting it puddles or drips. This product is vegetables but also many ornamental extremely toxic. plants. The closely related virusimpatiens 6. Always read and follow necrotic spot similarly has a very wide Figure 12: Thrips scarring of flowers. (Photo by host range, particularly among ornamental instructions on the label! J. Capinera.) plants. See fact sheet 2.947, Greenhouse Plant Viruses (TSWV-INSV) for more information on this serious disease. Fungus Gnats Management. Many strains are resistant Fungus gnats (Bradysia species) are to insecticides and their habits make them small, dark colored flies that jump and even harder to control. Egg stages are fly across the soil surface. Adult gnats are inserted into plant parts and later immature commonly seen as they collect around stages (sometimes called “pupae” and windows. Fungus gnats cause little or no “prepupae”) develop in soil where they are injury to house plants but create a serious inaccessible to sprays. nuisance problem. Problems are most Pyrethroid insecticides control some common during winter and early spring. thrips (onion thrips) but not the most Since these insects develop in potting soil, common types. Exposed stages are virtually any houseplant can be a host for controlled with soaps or oils. Adults are fungus gnats. attracted to sticky traps, particularly yellow Adults live for a few days and lay eggs or pale blue. in soil cracks and around the base of Where problems with tomato spotted plants. The pale colored larval (“maggot”) Figure 13: Fungus gnat adult. wilt or impatiens necrotic spot occur it is stage feeds on fungi and decaying organic critical to remove and destroy all infected matter. They also feed on root hairs of the plants immediately since they can serve as a plant which causes reduced plant vigor. A renewing reservoir of the disease. generation can be completed in one month. Table 2. Summary of cultural and mechanical controls for houseplant insects and mites. Pest Non-chemical Controls Spider mites Increase humidity around the plant; periodically hose with jet of water. Greenhouse whitefly Use sticky traps to capture the adult whiteflies; vacuum plants to capture adult stages. Brown soft scale Physically pick or rub scales to kill them; coat individual scales with alcohol. Mealybug Coat individual mealybugs with alcohol; grow plants under conditions that allow moderate growth to reduce succulence favored by many mealybugs. Fungus gnats, Springtails Avoid excessive watering; avoid use of high organic matter soils or fish emulsion fertilizers which can favor development of fungi eaten by fungus gnats. Aphids Periodically hose the plant with a vigorous jet of water. Crush individual aphids. Yellow sticky traps may capture winged adults.

Table 3. Summary of expected performance of insecticides available for use on houseplants. Whitefly Mealy Spider Soft Armored Fungus gnat Insecticide nymphs/adults bugs mites scale scale Aphids (larvae/adults) Comments Horticultural oil C/N S C C C S N/N Primarily acts by smothering; no residual effects. Insecticidal soap S/N S S S* S* C/S N/N Contact insecticide with no residual effects. Pyrethrins, resmethrin, sumithrin, tetramethrin N/S S S/N S* S* S/N N/C Short persistence (hours). Permethrin, cyfluthrin S/C C N S* S* S/N N/C Moderately persistent (days) pyrethroids. Bifenthrin S/C C C/S S* S* S/N N/C Moderate persistent pyrethroid with some activity against spider mites. Neem insecticides C/N N N N N S C/N Acts to disrupt growth of some developing insects. Neem oil C/N S S S S S N/N A plant-derived horticultural oil. Disulfoton S/S S S S N S N/N A systemic insecticide applied to soil. Highly toxic. Imidacloprid C/C C N C S C N/N A systemic insecticide usually applied to soil; some foliar treatments are available for houseplants. Bacillus thuringiensis var. israelensis (H-14) N/N N N N N N C/N A bacterial disease of certain fly and gnat larvae. C - Can provide control of the pest; S - May suppress numbers of the pest; N - Not effective for control of the pest. * Effective against the newly hatched, crawler stages of scales only.

Management. Fungus gnats are var. israelensis or (H-14 strain) is highly native insects and are common in lawns effective as a soil drench. Also some and garden soils. Reinfestation from neem products are labeled for soil drench these outdoor sources is very likely and purposes and can control fungus gnat difficult to prevent completely. However, larvae. Unfortunately neither of these fungus gnat populations can be reduced products is commonly sold in Colorado to levels that are not a serious nuisance. and may be more readily acquired via Since fungus gnat larvae feed primarily mail order. Figure 14: Fungus gnat larvae. on decaying plant materials, changing soil moisture conditions is the most Other Flies important step to take. Watering should Sometimes other flies are associated be limited so that the soil surface can dry with indoor greenhouses. Where algae between waterings. develops shore flies may become Some adults can be captured on sticky established. These flies are slightly larger cards. However, as they are very short than fungus gnats and don’t pose nuisance lived they may have laid many eggs before problems. However, adults regurgitate capture. Adults can also be suppressed dark material and “fly specks” on plants. In by sprays of pyrethrins and pyrethroid stagnant water rich in organic matter moth insecticides. However frequent application flies can breed. These minute flies have Figure 15: Shore flies and associated “fly is required to reduce adult abundance a broad feathery wing that superficially specks”. and egg laying, particularly when using resembles a small moth. Both shore insecticides of short persistence. flies and fungus gnats are managed by Larval control is more effective. The eliminating breeding sites. biological insecticide Bacillus thuringiensis Springtails Springtails are small, gray or cream- colored insects that feed on decaying organic matter in soil. They are most often recognized by the habit of many species to jump on the soil surface, like a small flea. They are most often observed in potted plants shortly after watering brings them to the surface. Springtails cause little, if any damage to houseplants but can be a nuisance problem. Limiting water reduces springtail numbers. Figure 16: Springtails.

Table 4. Dilution rates for small-quantity sprayers. Some pest management products sold as concentrates state use rates as a percentage dilution or dilution ratio with water. The following table is prepared to assist in computing the approximate amount to add for gallon, quart or pint quantities of spray. Dilution ratio Percent Approximate amount to add to water volume: (ingredient to water) dilution gallon quart pint 1:99 1% 2.5 Tbsp(-) 2 tsp(+) 1 tsp(+) 1:49 2% 5 Tbsp(-) 4 tsp(+) 2 tsp(+) 1:32 3% 8 Tbsp(+) 2 Tbsp(+) 1 Tbsp(+) 1:24 4% 10 Tbsp(-) 2.5 Tbsp(+) 4 tsp(+) 1:19 5% 13 Tbsp(+) 3 Tbsp(-) 5 tsp(-) Tbsp = tablespoon; tsp = teaspoon. 3 teaspoons (tsp) = 1 tablespoon (Tbsp) + Will produce a solution of a slightly higher concentration than indicated. - Will produce a solution of a slightly lower concentration than indicated.

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