FROM THE AUTHORr: Back several years ago when I first started growing orchids at home, I sent away to a place in Colorado for some plants. This was a friend of mine, I thought. (We recently had a disagreement, so I wasn't sure.)I received this big, long-awaited box of plants. When I opened it, I figured out quickly that we weren't friends anymore. Anyway, when I unwrapped the pots of plants, out dropped --or rather crawled-- all sorts of critters. There were beetles, centipedes, slugs and some other scary bugs; and those were just the ones that fell out. I also found various other creepy crawlers and slithery things in the pots and on the plants. I'm pretty sure he didn't have many bugs left in his greenhouse.
I had to figure out right away how to bug-proof my orchid collection and other houseplants. I immediately repotted everything into new orchid mix, cleaning every plant part under running water as I went. These plants were then isolated for a month or two to make sure I caught all the critters. Needless to say, that was the last purchase I made from that ex-buddy.
This page is a general overview of plant pests and their cures in the home. Check these links for specific information on Pest Identification, and Greenhouse Pest Control. See Links below for more information.
The following is an excerp from an article from the Colorado State University Cooperative Extension.
Managing Houseplant Pests
by W.S. Cranshaw 1
- Many houseplant insect problems are introduced by infested plants.
Carefully check plants before purchasing and quarantine them in a separate area for a few weeks to avoid introducing new pest problems.
- Changes in cultural practices can help control many houseplant insects, such as fungus gnats.
- Several insecticides are available to control houseplant pests. For some pests, biological controls also exist.
Houseplants are susceptible to attack by many insects and mite pests. Some of these houseplant pests can cause extensive damage to the appearance and health of the plant while others are simply a nuisance. Plants that are not vigorously growing and/or are under stress may be particularly susceptible to insect and mite injuries.
Stress can come from many sources, but mainly from poor care. When a plant becomes stressed due to over watering, under watering, too little light, humidity, etc, its natural resistance is diminished, sometimes to the point of allowing an infestation to appear seemingly overnight. This is not so. Insects target stressed plants. What appears as an overnight infestation is really the result of neglect. The insects were there, but not noticed. To avoid this, check youir plants often for signs of stress and insect pests.
Infestations of scale insects (mealybugs and whiteflies) are almost always established from infested plants recently purchased or received as gifts. As a precaution, all new plants should not be placed with existing houseplants for at least three weeks. A careful inspection at the end of this time helps determine the presence or absence of pests.
Methods Used to Control Houseplant Pests
Syringing plants. Many household plant pests can be controlled, at least in part, by washing the plant periodically with a vigorous jet of water. This is particularly effective for spider mites and aphids, which are most readily dislodged.
Cultural changes. Watering affects houseplant pests in a couple of differerent of ways. Excessively moist soil favors the development of problems with fungus gnats. However, plants placed in very hot, dry sites are prone to problems with spider mites.
Handpicking. Larger houseplant insects can be controlled by handpicking. This is especially useful for scale insects and mealybugs. Regularly using small, hand-held vacuums assist in controlling whiteflies.
Trapping. Yellow sticky traps can be useful to reduce the number of insect pests that fly – whiteflies, winged aphids, and fungus gnats. These traps are sold commercially or you can easily make them by cutting bright yellow cardboard and covering it with petroleum jelly or some other sticky material. However, trapping alone will not entirely eliminate problems because much of the population, including the younger stages, remain on or about the plants.
Sanitation. Seriously infested plants are often best discarded because they usually require lengthy and extraordinary efforts to control the pests. They may also serve as a source for infesting other plants. You can use periodic “host-free” intervals to cause insects that survive for short periods without feeding to die out. [Keep your plants clean by clearing out dead leaves or other plant parts. These are often hiding places for unwanted insects.]
Biological controls. Under certain conditions, natural enemies of houseplant pests are effective in reducing the problem to acceptable levels. However, they are relatively difficult to acquire and are usually available only through specialty suppliers.
Alcohol. Sprays of alcohol, or alcohol dabbed onto insects, is well known as a useful control of mealybugs. However, using alcohol on plants may cause injuries such as leaf burn. Carefully test a small part of the plant if you attempt to use this method.
Insecticidal soaps. Insecticidal soaps (potassium salts of fatty acids) are one of the most commonly available houseplant insecticides. These are used as dilute sprays (one to three percent concentration) and can help control many houseplant insects and spider mites. Many liquid hand soaps and dishwashing detergents also have insecticidal effects, although there is potential for plant injury with such treatments.
Horticultural oils. Diluted sprays of oils (petroleum distillates, mineral oils) are some of the most useful insecticides for houseplant pests, capable of controlling scales, young whiteflies and spider mites. These are highly refined oils that primarily act by smothering.
Neem. Some houseplant insecticides are derived from seed extracts of the neem plant, a commonly grown tree in many tropical areas. Neem seed contains materials that disrupt insect growth and is useful for control on developing whiteflies and some other insects. Neem seed also contains oils that may be used in a manner similar to other horticultural oils and is sold in products labelled as containing “clarified hydrophobic extracts of neem seed.”
Pyrethrins and pyrethroid insecticides. Pyrethins are a common ingredient in many houseplant and garden insecticides. They are a natural product derived from flowers of a certain (pyrethrum) daisy. Pyrethrins are fast acting, have a very short persistence (a few hours), and low toxicity.
Several “synthetic pyrethrins,” better known as pyrethroids, are also commonly used. These are synthetically manufactured insecticides based on the chemistry of the natural pyrethrins. Some of these pyrethroids, such as resmethrin and sumithrin, are also fast acting and have a short persistence like the natural product. However, other pyrethroids, such as permethrin, cyfluthrin, and bifenthrin, may persist in active form on foliage for several days. Pyrethroids may have differences in their ability to control houseplant pests, such as bifenthrin, which is much more effective than other pyrethroids against spider mites.
Systemic insecticides. Some insecticides, known as “systemic insecticides” have the ability to be absorbed by plants. Those used on houseplants are sold as granules or as stakes. They are applied to the soil for the roots to absorb.
Bacillus thuringiensis var. israelensis (H-14 strain). A naturally occurring soil bacteria, Bacillus thuringiensis, has the ability to control many insects. It is a commonly used microbial insecticide. Different strains of this bacteria occur which may have different effects on insects. For example, one strain (“kurstaki”) is commonly sold to control caterpillars on vegetables and ornamental plants. Another strain, “israelensis” or “H-14,” can control certain larvae of gnats, blackflies, and mosquitoes. It is sold under the trade names Gnatrol and Knock-Out Gnats to control fungus gnat larvae in houseplants.
Notes on using pesticides:
Follow the cautions listed below when using pesticides on houseplants to avoid exposure and plant injury.
1. Only use pesticides that are specifically labeled for use on houseplants. Most yard and garden pesticides do not allow this use.
2. If possible, take the plant outdoors before spraying to minimize pesticide exposure within the home.
3. When using aerosol sprays, do not apply closer than 18 inches to the plant or injury may occur from the spray. This precaution appears on most label use directions.
4. Avoid treating plants that suffer from environmental stresses such as temperature extremes or drought to minimize potential plant injury. [Let the plant rehydrate or come to room temperature first.]
5. If granules or plant stakes containing DiSyston are used, use extra care when watering. Excess water may carry this insecticide as it puddles or drips. This product is extremely toxic.
6. Always read and follow instructions on the label!
Click here for pest identification.
Ohio State University, Yard and Garden Section
1W.S. Cranshaw, Colorado State University Cooperative Extension entomologist and professor, bioagricultural sciences and pest management.