House Plant Pest Control Measures

John F. Baniecki, Ph.D.
WVU Extension Service
Plant Pathology and Entomology Specialist
August 2000

There are a number of ways of controlling pests of house plants, some utilizing pesticides, some consisting of non-pesticidal alternatives. What the homeowner should use varies with the pest encountered, the number of plants infested, the size of the infestation, and the personal inclination of the homeowner. The following should be given consideration.

Handpicking - If one or a few plants are involved, you may be able to control aphids and mealybugs by removing them with a toothpick or tweezers. Caterpillars may be picked off plants by hand and destroyed. Cutworms, slugs, and snails may be found in their hiding places during the daytime and destroyed or picked from the plants at night when they feed.
Washing - Washing with soapy water and a soft brush or cloth may be all that is needed to remove aphids, mealybugs, and scale insects from broad-leaved plants. Use 2 teaspoons of a mild detergent to a gallon of water.
Use of alcohol - An easy way to control a light infestation of mealybugs or aphids on one or two plants is to wet and remove the insects with a swab that has been dipped in alcohol. Use a swab made from a small, thin stick and a tuft of cotton to dip in rubbing alcohol.
Preventing infestation - Examine cut flowers and new plants brought into the home to be sure they are free of pests. It's a good idea to isolate new plants for at least a month before placing them with other plants. During this time you can watch the new plants and discover any infestations that develop. Using sterilized soil for potting may prevent the development of infestations of such soil pests as springtails, psocids, and earthworms.
Pressurized insecticide spray - Relatively few insecticides have been registered by the Environmental Protection Agency for use on plants within the home. Those products that have been cleared, often consisting of several active ingredients in combination, are usually specially formulated for this use. Such ready-to-use spray preparations for plants come in pressurized cans with pushbutton sprayer tops. These preparations are available in department, hardware, and garden-supply stores. When buying a pushbutton spray, read the label on the container to be sure the spray is one that can be used safely on plants. Some insecticide sprays in pushbutton cans that are made for uses other than spraying plants contain oils or other materials that will kill plants or burn foliage. Pushbutton plant sprays contain small quantities of rotenone, pyrethrins, or other killing agents. They may be used to kill pests that can be hit readily with the spray, such as aphids and whitefly adults on plants, or whitefly and fungus gnat adults swarming near the plants.

To apply, follow the directions on the container.

Pest Control Measures - Insects and Related Pests

Aphids - House plant pressurized insecticide spray. Few aphids - handpick, wash, or use alcohol.
Caterpillars - Handpick. House plant or house and garden pressurized spray.
Cyclamen Mite - Trim off badly injured plant parts where practical. Immerse infested plants, pot and all, for 15 minutes in water held at 110°F. Success of treatment depends on careful control of water temperature.
False Spider Mites - Trim off badly injured plant parts where practical. Immerse infested plants, pot and all, for 15 minutes in water held at 100°F. Success of treatment depends on careful control of water temperature.
Fungus Gnats - If adults are numerous, a pyrethrum fly spray will control them.
Mealybugs - If one or a few plants are infested, control mealybugs by washing, by handpicking, or by using alcohol. Isolate treated plants to avoid reinfestation.
Millipedes - Eliminate hiding places and excessive organic materials where possible.
Scales - If only one or a few plants are infested, washing with soapy water may be a practical way to control scale insects. Heavily infested plants should be discarded.
Slugs and Snails - Eliminate hiding places--under pieces of wood or pottery, fallen leaves, or mulches. Put out a few pieces of shingles or boards for traps. Collect and destroy trapped slugs and snails every day or two; look for them under pots and pot rims. Collect slugs and snails from plants at night. If further measures are needed, use a commercial slug and snail bait containing metaldehyde or methiocarb. Follow label directions. To make the bait more attractive, you may moisten it with beer. For beer useage, place shallow dishes of beer in the vicinity of the infested plants. The pest will crawl into the beer and drown. The dishes should have straight sides to make it easier for the snails and slugs to crawl in.
Sowbugs and Pillbugs - Spray soil surface, under boardwalks and benches, along foundations, or other infested areas with malathion. Follow label instructions.
Spider Mites - Syringe tough plants with a forceful spray of water to break up (Red Spiders) webbing and dislodge mites. Dip or spray plants, using malathion or Safer's soap within 2 days after syringing. Treat tender plants with malathion or Safer's soap. Be sure to wet the undersides of leaves. Before spraying, mist plant with water to highlight webbing. Pick off webbing to insure good coverage of insecticide. Several applications at weekly intervals will be required to control mites.
Springtails - Spray soil surface, pots, saucers, shelves, and affected plant parts with malathion. On sensitive plants, water soil to bring springtails to the surface and then use a pyrethrum spray.
Thrips - Use pressurized house plant insecticide spray.
Whiteflies - Spray plants. Use house plant Safer's soap spray. Wet the underside of the foliage. Several applications at weekly intervals may be required. Resmethrin is effective and available as a spray or aerosol.

Diseases

Bacterial diseases: Common hosts of bacterial diseases are diefenbachia, philodendron, English ivy, pilea, pellionia, aglaonema, dracaena, monstera, and pothos. These plants develop dark green, water-soaked spots that turn tan, dark brown, or black with a yellow border. Spots can enlarge enough to cover an entire leaf. Stems and petioles can also be infected. Remove diseased portions of the plant with pruners sterilized in 70% alcohol after each cut.

Nematode diseases: Nematodes are tiny roundworms that live in and feed on plant tissues, especially roots. Infected plants are often stunted, have leaves with brown lesions, and roots with nodules. Good sanitation including soil sterilizations helps to control nematodes.

Virus diseases: Viruses are systemic disease-causing agents that are often transmitted by juice-feeding insects. Symptoms of virus diseases are diverse, but are often manifested as vein banding, mosaic (dark and light green patterns), flecking, ring-spotting, or yellow blotching. Stunting can also be seen. There is no control except to eliminate diseased plants. Spread of these diseases from one plant to another is unlikely.

Powdery Mildews: Powdery mildews are often found on grape ivy, kalanchoe, begonias, or pileas. A white growth appears on leaves, flowers, or stems that does not usually kill the plant, but reduces its quality. Reducing humidity and cold drafts helps to control powdery mildews.

Water Mold Rots: These diseases cause root, stem, and cutting rots, resulting in poor growth, yellowing, or stunting of the plant top. Improve drainage, aeration, and watering frequency of the plant. Keep fertilizing salts at a reduced level.

Root and Stem Rots: Rots of stems and roots can be controlled by sanitation and careful inspection of plants before they are purchased.

Fungal leaf spots and blights: Leaf spots are generally caused by splashing water from the soil on to the plants. This can be avoided. Watering in the morning also helps to control these spots.

General Diagnostic Guide for Indoor Plants

Symptom 1: Brown or scorched leaf tips Possible Causes

Poor root health from overwatering, exfessive soil dryness (especially between waterings), excessive feritlizer or other soluable salts in the soil
Specific nutrient toxicities (such as fluoride, copper, or boron)
Low humidity
Pesticide or mechanical injury

Symptom 2: Leaf spots, blotches, blemishes, blisters or scabby spots
Possible Causes

Intense light (sunburn) associated with a recent move of the plant or excessive soil dryness and wilting.
Chilling injury (below 50°F).
Chemical spray injury.
Overwatering.
Fungal or bacterial infections (rare unless plants have recently come from a field or greenhouse).

Symptom 2 A: - Foliage yellow-green; older leaves
Possible Causes

Insufficient fertilizer, expecially nitrogen.
Poor root health due to pot-bound growth, compacted soil, or poor drainage.
Insufficient light.

Symptom 2 B: - Foliage yellow-green; newer leaves
Possible Causes

Soil pH (acidity) imbalance.
Trace element imbalance.

Symptom 2 C: - Foliage yellow-green; general
Possible Causes

Too much light.
Insufficient fertilization.
High temperatures, expecially when associated with dryness.
Insect infestation or root rot disease.

Symptom 4: Leaf drop
Possible Causes

Poor root health from overwatering, excessive dryness, excessive fertilization or other soluble salts in the soil, compacted soil or pot bound roots.
Sudden change in light, temperature, or relative humidity.
Root rot disease.

Symptom 5: Wilting or drooping of foliage
Possible Causes

Poor root health from overwatering, excessive dryness, excessive fertilizer or other soluble salts in the soil, compacted soil, or a poorly drained container.
A toxic chemical poured into soil.

Symptom 6: Roots brown in color, soft or rotted; roots with tissue that can easily be "slipped off" leaving behind the string-like center tissues; roots massed or bottom of pot. Associated with one or more of the symptoms noted above.
Possible Causes

Poor root health from overwatering; excessive dryness, excessive fertilizer or other soluble salts in the soil, compacted soil, or a poorly drained container.
A toxic chemical poured into soil.
Over- or under-watering.
Root rot disease.

Symptom 7: Yellowed leaves with tiny speckling; leaves later bronzed and drying; webbing noted near growing points.
Possible Causes

Spider-mite infestation.

Symptom 8: Leaves covered with a sticky substance; mold growing on leaves; tiny brown or white objects seen on leaves or in crotches of branches; leaf drop or branch dieback; leaf or growing point distortion.
Possible Causes

Scale or mealy bug infestation.