House Plants: Insects and Related Pests

 
 
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  Prevention | Control | Aphids | Fungus gnats | Mealybugs | Millipedes | Mites | Springtails | Scales | Thrips | Whiteflies

Even with the best of care, the indoor gardener may encounter an insect problem among his plants. Regular, careful inspection of plants is an important part of insect control. Particular attention should be paid to the undersides of the leaves where pests are most often found. In many cases, the presence of insects on house plants is not realized until the plants begin showing signs of feeding damage - commonly spotting, streaking, discoloration, wilting or deformation of the leaves. Population build-up may occur rapidly as a result of the constant warmth and lack of predators found in most houses and home greenhouses. Under these conditions many common houseplant insects and mites can multiply rapidly, completing their development in less than two weeks and constantly producing new generations.

Prevention

Pest infestations can be discouraged by washing plants every two or three weeks. You can do this easily by rinsing them in the sink or shower, or under a hose outdoors in the summer. Invert small plants and swish them in a bucket of tepid water. Wipe large, cumbersome plants clean with a soft, wet cloth or sponge, paying close attention to the undersides of the leaves. The addition of a little mild soap (not detergent) will help the water to spread into small cracks and crevices and through hair on the leaves and stems. Rinse with clear, tepid water. Regular bathing also improves the overall health and appearance of the plant by removing dirt and dust from the pores.

Pasteurized soil should always be used when repotting plants. Either buy prepackaged soil that is labelled as sterilized or sterilize it yourself by dampening and heating in the oven at 85C for 30 to 40 minutes. This kills all stages of any pests which may be present in the soil.

Pests often find their way into the home on newly purchased plants. Store-bought plants should be inspected carefully for signs of infestation before being brought home, and then isolated from other plants for two to three weeks to ensure no stowaways are present. A 10x magnification hand lens is a useful tool for detecting unwanted bugs, particularly immature ones.

Plants placed outdoors for the summer are liable to be host to insects by summer's end. Before bringing plants indoors in the fall, inspect them carefully, wash, and keep isolated from other plants for two weeks. Cut flowers from the garden may also carry pests, so keep them away from house plants.

Control

Any plant suspected of having a pest problem should be isolated. Early infestations can be eliminated by physical means such as hand-picking or removing the offenders with tweezers. Insecticidal soap is a product that can be used to remove unwanted guests. Be sure read and follow label recommendations. Testing the product on a couple of leaves 4 days prior to applying the product to the whole plant will give a good indication if the plant can not tolerate the soap product.

Do not expect a pest problem to disappear after one treatment. Adult insects and other pests may be hidden in leaf axils or under leaves. Eggs laid in the soil or on the plants are also likely to survive the initial treatment. Perseverance is the key to eliminating pests before they eliminate your plants.

For severe infestations the most practical solution may be to throw the plant away, soil included. If possible, rescue cuttings, clean thoroughly and raise new plants. If the plant is valuable or many plants are infested, you may have to resort to a chemical insecticide.

Identify the pest before choosing any chemical. Some insecticides are effective against only a few pests, and you are exposing your plant unnecessarily to toxic substances if you spray with any product you happen to have on hand, regardless of whether it specifies the actual pest attacking your plant. Some plants are also sensitive to certain chemicals, and can react with symptoms such as browning, spotting or death of leaves and plant.

Choose a pesticide specifically formulated for house plants, and read the label carefully to make sure it is suited to both your plants and any pests attacking them. Do not use garden insecticides on house plants. They are strong smelling and more toxic to both you and your house plants. Once you have found a suitable product, use immediately if it requires dilution, as some materials decompose rapidly in water. This means making up only as much as you require, or applying ready-to-use products. When using aerosols, keep to the recommended spraying distance (usually 45 - 60 cm) since the propellants can cause leaf browning.

It is advisable when spraying a limited number of plants to spray in a basement or spare room (outdoors in summer) away from habited areas.

Never apply more than one type of chemical at a time. The mix may be much more toxic than the materials separately. Alternate instead between two or more types of chemical to prevent resistance by the pest. Wash off the plant immediately in lukewarm, soapy water if you suspect it has been overdosed.

The following insects and other pests are those most commonly encountered on houseplants in the home.

Aphids

Description and damage
Aphids, also called greenfly or plant lice, are small, pear-shaped, winged or wingless insects, usually pale green but sometimes pink, brown, black or yellow. They are usually found in colonies on the undersides of leaves or on new growth. Aphids suck plant juices, causing the leaves to wilt and curl, and eventually yellow and fall off. Discolored spots may appear, growth becomes stunted, and new buds are blasted or deformed. The honeydew they excrete leaves a shiny, sticky film on the leaf surfaces, which acts as a medium for the growth of a black sooty mold. Aphids are also carriers of plant disease viruses which they inject into the plant while feeding. Most aphids found on indoor plants are wingless virgin females which continuously give birth to living young. They have the potential to build up rapidly if left unchecked.

Control
Cultural - Prune off heavily infested growth.
Or apply one of the following materials:

  • Insecticidal soap - Apply as a foliar spray.
Fungus gnats

Description and damage
Fungus gnats are small, black, delicate flies often found hovering around plants. Adult gnats do not feed, but lay eggs in the soil which hatch into white, blackheaded, legless maggots. These maggots feed on fungi and decaying vegetable material but may also attack fine plant roots and cuttings.

Control
Larvae do not survive well in dry soil, so avoid overwatering and allow the soil to dry out occasionally. Adding 1.2 cm of sharp sand on top of the soil in plant pot will discourage egg laying by the adults. If the problem persists apply one of the following materials:
  • Yellow sticky traps placed near the infested plant to capture the adults
Mealybugs

Description and damage
Mealybugs are small pink insects which cover themselves with a white waxy material. The eggs are also covered in this material, giving the appearance of bits of white fluff on leaves, stems and at nodes. Like aphids, mealybugs excrete honeydew which leaves sticky patches on the leaves and acts as a medium for the growth of a black sooty mold. Mealybugs suck plant juices causing stunted growth and eventually death of the plant.

Control
Hand picking or a thorough washing provides the best control, but mealybugs are easily concealed and almost daily checking is necessary to eliminate them. A cotton swab dipped in rubbing alcohol and touched to each insect works well. If numerous, apply one of the following materials:
  • Insecticidal soap: Apply as a foliar spray weekly as required.
Millipedes

Description and damage
Millipedes are not true insects but are often included when discussing pests of houseplants. They have long, many-segmented, hard-shelled bodies with two pairs of legs to each segment. Those found in greenhouses are between 10 and 25 mm long when fully grown and are light brown to dark brown or grey in color. Millipedes are mostly scavengers, feeding on decaying vegetation, however, they will feed on small roots, bulbs and seedlings. They may multiply in the soil to the extent that they overcrowd the pot and migrate out in search of new host plants. This is often the first indication that the soil is infested with millipedes.

Control
Cultural - Repot plants in pasteurized potting soil in clean pots.

Mites

Description and damage
Mites are not insects but are one of the most frequent pests of houseplants. The species most commonly encountered is the two-spotted spider mite which is found on a wide range of plant hosts.

This mite is rather small and is yellowish with two black spots on the back. Small, white speckles on the upper leaf surface are usually the first sign that mites are present. Check the underside of such leaves for round, white eggs, mites and webbing. The leaves of heavily infested plants become bronzed or yellowed and eventually the plant dies. Cyclamen mites are an even smaller, glassy-white mite which is found most often on cyclamen, African violet and ivy, causing severe stunting and deformation of new leaves. It is not as commonly encountered as the two-spotted mite, and is almost impossible to see with the naked eye.

Control
Frequent misting or washing of the plants with soapy water will help discourage mite build-up. To eliminate them apply one of the following materials every 7-14 days, as necessary, paying particular attention to the undersides of the leaves.
  • Insecticidal soap - Apply as a foliar spray. Target the undersides of the leaves and where leaves join the stem or crown. Before applying treatment to African voilet be sure to test a small area a few days before treating the whole plant to avoid injury.
Springtails

Description and damage
Springtails are common soil inhabitants often found in houseplant soil. They can be seen hopping on the surface after watering. Most species are white or black and large enough to be seen with the naked eye. They thrive in moist soil where they feed on decaying organic matter. Their presence is often an indication of over watering. If numerous, they may attack seedlings or tender plant parts, but damage is minimal.

Control
Reduce watering and use sterilized or pasteurized potting soil when transplanting.

Scales

Description and damage
Scale insects are round or oval insects related to aphids but protected by a hard waxy, shell-like covering. The color of mature scales ranges from tan to brown or black. The mature scales are females which lay their eggs beneath the scale and then die. The pale newly hatched nymphs are mobile but soon settle down and remain attached to one spot where they secrete a scale over themselves and feed by sucking plant sap. Males are small and seldom seen. Scales also excrete sticky honeydew on which a black mold grows.

Control
Mature scales are protected from insecticides and are best removed manually. Scrub off as many scales as possible with the aid of a soft brush such as a tooth brush. The nymphs can then be killed using one of the following insecticides applied to leaves and stems. Be sure to have good coverage of the plant to eliminate the crawlers.
  • Insecticidal soap - Apply as a foliar spray. Spray thoroughly. Repeat as necessary.
Thrips

Description and damage
Several species of thrips may infest houseplants. Thrips are small, slender pests, the young being white, yellow or orange and the adults brown or black.

Adults are hard to spot since they fly around the plant, especially when disturbed. They feed by rasping the plant tissue and sucking up the juice, causing a silvery speckled appearance and deformed leaves and buds. Usually the signs of damage are much more obvious than the thrips. Tapping the plant over white paper may disclose their presence. Some species leave dots of black excrement on the leaves.

Control
Cultural - Increase humidity and avoid high temperatures. Mist plants frequently.

Whiteflies

Description and damage
The greenhouse whitefly attacks both ornamentals and vegetables. Fuchsia, lantana, Jerusalem cherry, hibiscus and geranium are favorite ornamental hosts. The adult is a tiny white, fly-like insect which rests on the undersides of leaves and flies off the plant when disturbed. Nymphs are yellowish, green and scale-like. They become attached to the lower leaf surface soon after hatching and lose their ability to move. The life cycle is completed in four to five weeks.

Control
Cultural - Hang yellow sticky traps to attract adults.

Whiteflies have become resistant to many of the materials once used to control them.
  • Insecticidal soap: Apply as a foliar spray.
Adapted from Agdex 285/626-1.
 
 
 
 

Other Documents in the Series

 
  House Plants - Problems: Symptoms and Causes
House Plants: Diseases
House Plants: Insects and Related Pests - Current Document
 
 
 
 
For more information about the content of this document, contact Shelley Barkley.
This information published to the web on July 5, 2001.
Last Reviewed/Revised on October 28, 2013.