Fungicides can be an important component of the disease management program. However, it is important to remember that their use should be integrated with the use of sound cultural practices, a knowledge of pathogen and disease biology, and disease-resistant or less susceptible plants whenever possible.
Fungicides are only effective when infectious plant diseases that are caused by fungi are truly the cause of the problem. In some cases, pests and diseases follow other environmental imbalances and may not be the major problem. In cases such as these, the fungicide will help but is often not the total answer. Also, it is important to remember that fungicides are only effective if several rules are followed. First, the correct material must be selected. This depends on correct diagnosis and identification of the pathogen. Second, the chemical must be applied at the right time of year and frequently enough to protect plant material adequately. Third, fungicides must be applied properly over plant surfaces. These three rules depend on your making correct decisions based on correct knowledge. Too many people simply "spray and pray," and are often disappointed with the results.
You must be sure of what the problem is before proceeding. The most effective fungicides in use today have been developed for specific situations and specific diseases. To use these chemicals, you must spend time making a correct diagnosis. Extension specialists and agents, and the OSU Plant and Pest Diagnostic Clinic can assist you with the proper diagnosis.
Diagnosis leads to selection of the right material to do the job. Usually, several materials are effective against the type of disease you are dealing with. For instance, triforine, sulfur, or triadimefon all control powdery mildews. Before selecting any chemical, read the label. Can you carry out the instructions? Is the plant type listed on the label? If so, the chemical is registered for use on the plant and should be effective in providing disease control if used properly. If not, it may be illegal to use that particular pesticide.