When controlling insects and diseases when trouble does strike, your first step is to get accurate diagnosis from a reliable authority. Do the symptoms indicate a cultural deficiency, an insect of some sort, or a plant disease? And what specific deficiency, insect, or disease is indicated? Treatment is based on this information.
Certain kinds of insecticides are specific against certain types of insects. Some diseases respond to some fungicides, some to others. The required ingredient may be present in effective quantity in your general-purpose spray or dust, or it may not.
You have more leeway in choosing the method of application. Chemicals come in a number of different forms and can be applied in several different ways according to personal preference and convenience.
Dust - A dry insecticide, fungicide, or disinfectant blown in a thin, uniform layer over plant parts from a dust gun. Modern pliable plastic squeezer-dusters are handy for treating small plants or a few plants. Many other kinds of dusters are available for bigger jobs.
Wettable Powder - Dry powder that goes into suspended solution when mixed with water. Since the powder does not dissolve, the solution should be agitated continually to keep the suspension from settling out.
Emulsion Spray - Liquid, usually concentrated and mixed in directed proportions with large quantities of water, sometimes with oil and water.
Aerosol Bomb - Pressure-packed spray that spreads a fine, even mist, convenient for spot treatment or a small number of plants. These should never be held closer to plants than the distance stated on the label.
Drench - Liquid emulsion with which soil is soaked.
For any preparation or method of application, it is most important to read carefully every word of the manufacturer’s message on the label or package, and follow his directions to the letter. Insect poisons are also poisonous, in varying degrees, to humans and animals. Some are effective only when used at certain temperatures, or at certain times, or in certain ways.
Measure quantities exactly. Observe all precautions for safety. Note, too, whether the preparation is recommended for use as a preventive, and whether it should be repeated at regular intervals. Some insecticides kill only adult insects and have no effect on eggs. The treatment must be repeated as eggs hatch.
When spraying or dusting, cover all parts of the plant, and particularly the undersides of leaves where many diseases start and many insects hide. Dipping small plants headlong into a container of spray solution gives complete coverage. It may be wise to treat the soil around the plant as well as the plant itself.
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