Use soapy or plain water spray to control insect and mite pests.
Problems with indoor plants typically arise from improper care (too much or too little water and fertilizer), poor sanitation, adverse environmental conditions (low light intensity, low relative humidity), and insect or mite pests.
Whenever you detect insect or mite pests on an established plant in your home or office, isolate the plant immediately to prevent pests from spreading to other plants. As an additional precaution, wash your hands after touching insect- or mite-infested plants. You can decide later how or whether to attempt to control the pests. Sometimes control is not practical or effective, and it is better to discard the plant and purchase a new one.
The majority of indoor plant problems are caused by improper care and by environmental factors in the home. Get to know the growing requirements of each of your house plants.
Controlling Insect Pests and Mites
Keeping your indoor plants clean and inspecting them regularly are the best defenses against insect pests and mites. The most common indoor plant insect and mite pests are aphids, spider mites, mealy bugs, scales, whiteflies, and thrips (see Associated Links, below). The strategies against these pests depend on the pest and the plant. In some instances, control of the pest is impractical or nearly impossible once the pest is established. The best course of action in these situations is to discard the plant and obtain a new one. Some soft-bodied insects and mites can be removed by forcefully washing the plant leaves and stems with plain or insecticidal soap solution.
Controlling House Plant Diseases
If a purchased plant is disease-free, infectious disease will rarely be a factor in the indoor life of the plant. Of course, disease symptoms such as discolored stems (pdf) and roots or leaf spots that are present on plants when they are purchased will not disappear. These plants should be rejected.
Recognizing infectious diseases on flower, leaf, and stem parts of plants is sometimes more difficult than recognizing insect or mite pests because the pathogens cannot be viewed directly. Most often, the pathogens will be fungi.
A fungus grows on a leaf similar to the way mold grows on bread. Circular lesions (pdf) of growth sometimes overlap one another, giving a blotchy appearance. Concentric rings in the lesion give a “bulls-eye” appearance.
Bacterial diseases sometimes appear as oily, greasy, or water-soaked spots (pdf) on leaves. These are often visible by viewing the lesion from the underside of the leaf. Some bacterial diseases are systemic in nature and cause wilting (pdf) and general yellowing of plants. Systemic diseases may occasionally cause rotting or cankering of the stem tissue.
Infectious root rots can be diagnosed to some extent by direct observation of the root system. Off-color or brownish to blackish roots often indicate that root rot is present. Being able to pull off outer root tissue with your fingers (leaving the string-like center of the root behind) is a good sign that root rot is present. To determine the health of a root system, you should know what a healthy root system looks like.