In addition to direct losses in yield and quality, financial losses from plant diseases can arise in many ways.Farmers may have to plant varieties or species of plants that are resistant to disease but are less productive, more costly, or commercially less profitable than other varieties. They may have to spray or otherwise control a disease, thus incurring expenses for chemicals, machinery, storage space, and labor. Shippers may have to provide refrigerated warehouses and transportation vehicles, thereby increasing expenses. Plant diseases may limit the time during which products can be kept fresh and healthy, thus forcing growers to sell during a short period of time when products are abundant and prices are low. Healthy and diseased plant products may need to be separated from one another to avoid spreading of the disease, thus increasing handling costs.
The cost of controlling plant diseases, as well as lost productivity, is a loss attributable to diseases. Some plant diseases can be controlled almost entirely by one or another method, thus resulting in financial losses only to the amount of the cost of the control. Sometimes, however, this cost may be almost as high as, or even higher than, the return expected from the crop, as in the case of certain diseases of small grains. For other diseases, no effective control measures are yet known, and only a combination of cultural practices and the use of somewhat resistant varieties makes it possible to raise a crop. For most plant diseases, however, as long as we still have chemical pesticides, practical controls are available, although some losses may be incurred, despite the control measures taken. In these cases, the benefits from the control applied are generally much greater than the combined direct losses from the disease and the indirect losses due to expenses for control.
Despite the variety of types and sizes of financial losses that may be caused by plant diseases, wellinformed farmers who use the best combinations of available resistant varieties and proper cultural, biological, and chemical control practices not only manage to produce a good crop in years of severe disease outbreaks, but may also obtain much greater economic benefits from increased prices after other farmers suffer severe crop losses.
Source: Plant Pathology by GEORGE N. AGRIOS