With winter fast approaching many of us have brought our houseplants indoors after spending the summer outdoors in the fresh air and sunshine. You may have brought some uninvited guests along with your plants. Iíll tell you about the five most common pest that go after houseplants and how to control them.
For those of us who garden both indoors and out, our battle with insects is never-ending. After spending summers outdoors many times pests will hitchhike indoors in our plants. Even if we inspect them and see no visible signs, there may be unhatched eggs in the soil. After a short period in the warm environment of our homes these pesky critters begin to hatch. They can spread quickly to other plants and their cycle of life can continue if we don't control them. Let's discuss the five most common pests and how to control them.
Mealybugs are small (1/16-1/4 inches long), flattened, oval insects appearing as miniature sow bugs. They are covered with white, powdery wax that resembles finely ground meal, thus the origin of their name. Many species are ornamented with filaments of wax around the edge and end of their body. Mealybugs are related to scales, aphids, and whiteflies. Although there are more than 275 species of mealybugs in the United States, two main species are commonly found on houseplants: the citrus Mealybugs and the long tailed Mealybugs.
The citrus mealybugs has been a recognized pest of citrus and ornamental plants in the United States since 1879. It is said that this species will feed on every flowering species grown in the greenhouse. Adult female citrus mealybugs produce from 300 to 600 eggs, which are deposited in a white, fluffy case called an ovisac. These ovisacs are commonly seen under leaves and along the stems of houseplants. Adult females have an average lifespan of 88 days.
The long tailed mealybug also has a wide host plant range. Its name is derived from the long waxy filaments extending from the rear of adult females. Fewer eggs (about 200) are produced by adult females, but this species produces live young and no ovisacs are present. Mealybugs have needle-like sucking mouthparts. Feeding activity can cause a yellowing of host leaves, distorted growth, premature leaf drop, and, with heavy populations, plant death. Mealybugs also produce large amounts of a sweet, sticky liquid waste product called honeydew. A black fungus called sooty mold may grow on the honeydew. This pest is usually brought into the interiorscape on an infested plant.
One of the best ways to manage mealybugs on houseplants is to carefully check plants being considered for purchase and reject any infested plants. Quarantine new plants for 7 to 10 days in an isolated spot, and check for signs of mealybugs or other household pests before adding the plants to your interiorscape. Other suggestions for controlling mealybugs include the following:
Dabbing each insect with an alcohol-soaked cotton swab
Gently rubbing the insects from leaves or stems
Placing the plant in a tub or shower stall and knocking them off with a brisk water spray
Carefully washing plants with soapy water; one tablespoon of liquid dish detergent in one quart of water is a good ratio to use.
Spraying houseplants with a registered insecticide; active ingredients include azadirachtin, permethrin, pyrethrin, resmethrin, and rotenone
One of the easiest houseplant insect pests to recognize is the whitefly. These sap feeders are not really flies - they just look like they are. Actually, they look more like tiny white moths, but they are the size of gnats, about 1/16 inch long. You might notice them sitting on the underside of an infested leaf, usually the youngest leaves. More likely you will notice the tiny adults when they flutter off the leaf as you water or handle the plant. They are easily disturbed but fly only a short distance before they quickly return to the leaf. Whiteflies are not picky eaters. They have been found on more than 250 species of ornamental plants, including many common houseplants. A favorite place to look for whiteflies are on poinsettia, begonia, lantana, hibiscus and angel's trumpet.
It is very hard to get rid of whiteflies, so the first step is to do all you can to prevent infestations. Carefully check all new plants you purchase and the plants you bring indoors from the garden or patio in the fall. Keep a watchful eye on these plants. Check regularly and frequently for several weeks and be ready to launch the control assault at the first signs of infestation. One option for heavily infested or badly damaged plants is to give up and throw the plant away to minimize your losses and avoid spreading the problem to other plants.
Whiteflies are highly attracted to yellow objects, a behavior that is exploited in gardens and greenhouses by the use of yellow sticky traps. These sticky cards, stakes or tapes catch only the flying adults and are more appropriately used as a monitoring device.
Washing infested leaves (especially the undersides) with a moist cloth or sponge is one way to reduce whiteflies, but is labor-intensive and inefficient for large plants.
Finally, insecticides are available but control is usually marginal at best. Thorough application to infested leaf undersides is difficult to do and the eggs and nonfeeding resting stages are immune. Nymphs and adults can be sprayed to death, but repeat applications at weekly intervals are usually required. Systemic insecticides that are applied to the soil and taken into the plant via the roots may be available for foliage plants. Apply only ready-to-use insecticides specifically made for houseplants according to label directions.
Several species of scale insects commonly infest houseplants. These sap-feeding insects have a tan to brown shell-like covering or scale that protects the insect's body. Scales may be from 1/16 to 1/4 inch in diameter and are usually found on the stems and/or leaves. Some scales are hemispherical in shape, while others are oval and flat. Scale insects feed by sucking plant sap and may cause poor, stunted growth. Death of infested plants is possible in severe cases.
A large quantity of a sweet sticky liquid called honeydew is excreted by scale insects. Honeydew can make a sticky, shiny mess on the plant and nearby furniture and floors. A black fungus called sooty mold may grow on the honeydew.
Scale insects are difficult to control. There are several well-known remedies that can be tried in an attempt to eliminate scales from a houseplant. However, there is no easy, simple cure for a scale infestation. One possibility is to pick off individual scales or gently scrub (or rub) the scales loose from the leaves and stems. This is a labor intensive task that works only on small, large-leafed plants. Dabbing each scale with an alcohol-soaked cotton swab is another possibility on lightly infested plants.
Sprays can be used for scale control. Success will depend upon thoroughness and persistence. Insecticide sprays (aerosols or hand pump sprayers) made just for houseplants are available at garden centers. You can use a mild dish washing detergent in place of the commercial insecticide soaps. Use a dilute solution of 1 Tbsp. of detergent per quart of water. Soap sprays can be applied with a sprayer or used with a soft cloth while washing infested leaves and stems. Insecticides must be applied thoroughly, repeatedly and persistently (weekly for a month or more) to get good control.
Aphids are tiny, soft-bodied insects that may be black, green, or red. They are pear-shaped and have long legs. Some have wings and others are wingless. They usually feed on new growth of plants. You may find them on growing tips and flower buds, where they suck plant juices leaving sticky deposits of plant sap. These plant-sucking insects cause distorted leaves and buds. Some types feed on roots.
Wipe off plant leaves--top and bottom--with a damp cloth. This will remove insects and their eggs. If you have a large infestation, spray the plant with water several times to dislodge the pests from the plant.
Clean heavily infested plants with a cloth or sponge dipped in soapy water. Use mild dishwashing liquid that doesn't contain fragrance or other additives. Squirt 2 teaspoonfuls into 1 gallon of room-temperature water and gently wash the plant's leaves, undersides of leaves, and the base of the leaves where they attach to the stems. If this seems too tedious, cover the soil with a newspaper or plastic wrap, hold the plant by its base, and plunge the foliage into the soapy water. Wait 10 minutes then rinse the plant well using room-temperature water.
It's a good idea to spray your plant once a week with a solution of soap and water to prevent bugs from coming back. Remember to rinse the plant with clear water afterward.
Rubbing alcohol kills aphids, too. Dab them with a cotton swab soaked in rubbing alcohol. Repeat applications every 2 to 3 days. These methods works well, but use it with caution. Covering the whole leaf with alcohol damages plant tissue.
Spider mites are common pest problems on many houseplants. Injury is caused as they feed, bruising the cells with their small, whip like mouthparts and ingesting the sap. Damaged areas typically appear marked with many small, light flecks, giving the plant a somewhat speckled appearance.
Following severe infestations, leaves become discolored, producing an unthrifty gray or bronze look to the plant. Leaves may ultimately become scorched and drop prematurely. Spider mites frequently kill plants or cause serious stress to them.
Many spider mites produce webbing, particularly when they occur in high populations. This webbing gives the mites and their eggs some protection from natural enemies and environmental fluctuations. Webbing produced by spiders, as well as fluff produced by cottonwoods, often is confused with the webbing of spider mites.
Control Adequate watering of plants can limit the importance of drought stress on spider mite outbreaks. Disruption of the webbing also may delay egg laying until new webbing is produced.
Control on house plants can be particularly frustrating. There generally are no biological controls and few effective chemical controls (primarily soaps and horticultural oils). When attempting control, treat all susceptible house plants at the same time. Trim, bag and remove heavily infested leaves and discard severely infested plants. Periodically hose small plants in the sink or shower. Wipe leaves of larger plants with a soft, damp cloth. Reapply these treatments at one- to two-week intervals as long as populations persist.
On a personal note, I've had good luck with Bonide Houseplant Insect Control, a systemic product that is taken up by the roots and distributed throughout the plant.
Photos courtesy of Universities of Maryland, Illnois and Clemson University as well as Bonide
About Paul Rodman
Paul Rodman has been gardening for over 45 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is President Emertius of the Western Wayne County Master Gardener Association in Wayne County, Michigan. He currently serves as the greenhouse chairman of this group. Rodman has amassed over 5500 volunteer hours in the Master Gardener program.
Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the Organic Gardening.com web site.
He is a certified Master Canner and has taught classes on Home Food Preserving for 7 years.
He has lectured on various gardening topics throughout southeastern Michigan.
His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.