Control of Pests on Houseplants

Houseplants commonly become infested with insects or mites that cause damage ranging from cosmetic injury to death of the plant. Most often insects are found on houseplants because a plant is moved between the inside and outside of the home, infested plants are purchased, brought indoors and placed near other susceptible plants, or the pest is introduced to the inside of the home with native flowers, or on a person's body.

Isolate newly purchased plant material from other houseplants until you are sure they have no insect problems. Observe plants that you brought indoors for several days in a screened area before bringing the plants completely indoors. You may also thoroughly spray or wipe tops and undersides of leaves before bringing container plants indoors.

Pests attacking houseplants may be divided into three groups according to the damage they cause: chewing pests, sucking pests and nuisance pests.

Damage from chewing pests usually occurs rapidly and is evident immediately. Eliminate these pests as soon as you detect them. Symptoms of chewing pests include severed leaves, stems or flower buds, holes in leaves, and discolored areas on surface or margins of leaves or flower petals.

Sucking pests insert their mouthparts into plant tissue and suck out the juices. Some inject toxic compounds into the plant and some are capable of transmitting plant diseases. The symptoms of sucking pests often go unnoticed until the insects have become established in high numbers on the plant. The symptoms of sucking pests are wilting plant tissues, presence of sticky substance (honeydew) on upper leaf surface, curling or stunting of new growth, discoloration on leaves, or necrotic (dead) spots on leaves.

Nuisance pests cause no real damage. They are considered pests simply because their presence is not desirable. Such insects flying, crawling or hopping about detract from the beauty of a plant. Some nuisance pests multiply rapidly and are found in overwhelming numbers. You can easily stop such infestations with careful cultural management and properly applied insecticide treatments.

In cases where only a few plants are infested and the pests are relatively easy to find, remove the pests by handpicking. Caterpillars and beetles can often be eliminated by physically removing them. Mealybugs can often be removed with the aid of a cotton swab and alcohol. Cutworms, slugs and snails can be collected from their hiding places and destroyed.

When you detect houseplant pests early, you have enough time to diagnose the problem and to take curative actions before they do any serious damage. Table 1 lists the practices suggested to control each pest. If you must use pesticides always read the product's label to be sure it is labeled for use on the plants that need treatment.

Most insecticides control pests by contact with the insect or by acting as a stomach poison. Some products rely on a fumigating or vapor action to kill the target pest. Gain effective control by following four basic principles.

Foliage-Feeding Caterpillars. Many species of caterpillars have been observed feeding on houseplants. In most instances these pests have accidentally found their way into the home. These larvae are voracious feeders and even just a few can cause severe damage. Control can often be achieved by picking the larvae from the plants and destroying them.

Foliage-Feeding Beetles. Several species of beetles can feed on houseplants. Examples include the twelve-spotted cucumber beetle, green June beetle and several species of flea beetles. Beetles are more mobile than foliage feeding larvae and they can cause severe damage in a short time. Beetles may also be handpicked from infested plants when detected.

Thrips. Several species of thrips attack houseplants. Thrips are minute insects that feed on pollen and tender plant tissue. They range in color from yellow to tan to brownish-black. The adult forms have feather-like wings. Thrips are most frequently found in the blossoms of plants where heavy infestation can result in deformed, undersized or discolored flowers and brown edges on flower petals.

Snails and Slugs. Snails and slugs have fleshy, soft, slimy, legless bodies that range in color from whitish yellow to mottled shades of gray. These slow-moving pests attain a length of 1/2 to 4 inches and leave a slime trail behind them as they travel about a surface. They are predominantly greenhouse pests. They prefer to feed on tender plant tissue and occasionally damage small seedlings. These pests generally feed at night and hide beneath pots and other objects during the day. Treatment for slugs and snails should be applied when their presence is detected. Bait formulations are effective in controlling these pests.

Aphids. Aphids, or plant lice, are small, soft-bodied insects. Some aphids may have wings. They vary in color from green to yellow to black. Aphids are usually found on young, tender growth or on the undersides of leaves. They are frequently found in large numbers clustered together. They damage plants by sucking juice from leaves and stems. Aphids secrete honeydew; heavy infestations may result in the sticky substance covering the plant. Aphids reproduce rapidly so don't neglect infestations. Begin control measures as soon as aphids are found.

Scale Insects. Scale insects are small, soft-bodied pests that attach themselves to plant leaves and stems. They secrete a covering or "scale" over their body that serves as protective armor. There are many kinds of scale insects that attack ornamental plants. Scales can be white, red, brown or black. They appear to be flattened or minute turtle-shaped structures. Except for the crawler (the first stage of a scale insect), all life stages are completed under this protective covering. Soon after hatching, most scale insects attach themselves to the host plant, sink their sucking mouthparts into the plant, begin feeding, and never move from this feeding site. Some scales, like aphids, secrete honeydew that collects on the plant. Control often may be achieved simply by removing the attached scale insects from the plant. Heavily infested plant parts can be removed from the plant and destroyed. Insecticide applications are most effective when timed for presence of the crawler stage.

Mealybugs. Mealybugs are similar to scale insects. A mealybug's protective covering is a layer of white, waxy material that becomes heavier and more developed as the mealybug matures. These pests are usually found on new growth, on the leaves or petioles and on the flowers. They also can secrete honeydew and heavily infested plants become very sticky. Control light infestations by removing them with a cotton swab saturated in alcohol. Heavy infestations may be difficult to control, requiring two to three insecticide applications. Insecticide applications are most effective when timed for the presence of the young nymphal stages.

Whiteflies. Whiteflies are small, soft-bodied, gnat-like insects. The adults have two pairs of broadly rounded wings covered with a white, waxy powder. They are most commonly found on the undersides of leaves and fly out in a cloud when disturbed. The young (nymphs and crawlers) look very much like scale insects and are also found attached to the undersides of leaves. Whiteflies are also capable of excreting large amounts of honeydew and creating a sticky mess on the upper leaf surfaces of their host plant. Insecticide applications are most effective when timed for the presence of the nymphal and adult stages of the whitefly. Often several applications of insecticide are necessary to control a whitefly population.

Spider Mites. Spider mites, often called red spiders, are so small they can barely be detected with the unaided eye. These mites are common pests on many different houseplants and seem to be most damaging during periods of hot, dry weather. Damage appears as bleached-out or yellowish spots on the infested leaves. Heavily infested plants become stunted and may die. Spider mites have a rapid life cycle under ideal environmental conditions. Populations can explode in a short time. Examine susceptible plants frequently for mites and begin applications of miticides when you first notice the mites.

Springtails. Springtails, or Collembola, are minute, wingless insects about 1/10 of an inch long and vary in color from light gray to black. They are often found in high populations on the soil of potted plants or floating in water reservoirs of plant trays. Springtails feed on fungi and decaying organic matter, and some species occasionally feed on sprouting seed, roots and tender shoots. Problems with springtails can usually be avoided or corrected through proper watering procedures. When they are numerous, literally thousands may be found crawling on plants, pots or tables. Control springtails by treating outside of pots and saucers and the soil surface of potted plants with insecticide.

Sowbugs and Pillbugs. Sowbugs and pillbugs are commonly found in places with high humidity. The hard, curved shell of these insect-like creatures makes them appear to be miniature armadillos. They are oval, 1/4 to 1/2 inch long, and are gray to brown in color. They are most active at night and usually hide in loose soil or under any convenient cover during the day. Sowbugs and pillbugs usually feed on decaying organic matter but sometimes eat roots and tender plant parts. Maintain proper watering procedures to avoid pillbug and sowbug infestations. Control infestations with an approved insecticide by treating soil surface of potted plants and surfaces where pillbugs and sowbugs may hide during the day.

Millipedes. Millipedes are small worm-like creatures that often find their way inside the home in the soil of potted plants. They are dark in color, hard-shelled and reach a length of 1 to 2 inches. They have two pairs of legs on each segment. Millipedes feed primarily on decaying organic matter, but may attack roots and leaves of young plants. Inspect the soil of plants for millipedes before moving them indoors. Insecticide drenches applied to the soil are also beneficial in treating infested plants.

Fungus Gnats. Adult fungus gnats are small flies that resemble mosquitoes and are grayish to black, 1/8 of an inch long, slender and delicate. Fungus gnats breed in moist areas that are high in organic matter. The larval stages feed on fungi. Large numbers may be found reproducing in potted houseplants. Adults are attracted to light and often gather in large numbers at windows. Proper water management is very important in fungus gnat control. Avoid overwatering and use sterile potting soil to prevent infestations. Insecticide applications may be necessary at times to control heavy infestations. The larvae are best controlled with soil drenches or granular insecticide formulations applied to the soil surface and watered in. Adults can be controlled with sprays or aerosols when they are observed.

Pests	Control Practices
Foliage Feeding Caterpillars	(1) Handpick and destroy caterpillars. (2) When practical, move plants outdoors before applying pesticides.
Foliage Feeding Beetles	(1) Handpick and destroy beetles and/or beetle larvae. (2) When practical, move plants outdoors before applying pesticides.
Slugs and Snails	(1) Eliminate attractive sites. (2) Collect and destroy slugs and snails.
Thrips	Inspect plant material for thrips before bringing indoors. Thrips can enter the home on cut flowers, hanging baskets, foliage plants or your body.
Pillbug, Sowbugs, Springtails, Millipedes, Fungus Gnats	(1) Inspect plants and potting soil before bringing potted plants inside. (2) Avoid over-watering plants and creating favorable habitat for these pests.
Whitefly	(1) Inspect new plants for whiteflies before bringing them inside the home. (2) Isolate new plants or infested plants from other susceptible plant materials. (3) Physically remove whiteflies from plant using cotton swab moistened in alcohol.
Aphids, Scale Insects, Mealybugs	(1) Inspect plants frequently for aphid or scale infestations. (2) Control scales or aphids as soon as they are noticed. When practical, move infested plant material outside before application. (3) Aphids and scale crawlers may be washed from plant with strong stream of water or a soft brush dipped in soapy water. (4) Physically remove mealybugs from plant using cotton swab moistened in alcohol.
Spider Mites	Spider mites reproduce rapidly; frequently inspect plants for mite populations.

NOTE: FOR PESTICIDE RECOMMENDATIONS, CONTACT THE COBB COUNTY EXTENSION SERVICE AT 678 SOUTH COBB DR, MARIETTA OR CALL 770-528-4070.

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