Disease Diagnosis

The first step in turfgrass disease management is identifying the true nature of the problem. Diseases are only one cause of turf loss, and disease control measures will do nothing to alleviate damage from other causes such as insects or drought stress. It is therefore essential to determine whether the problem is disease, and if so, which disease. Disease management strategies that are effective against one disease may have no effect on, or may even worsen, another disease.

The three disease factors (susceptible grass, pathogen, and environment) provide the sources of information for diagnosis. Symptoms are the expression of the susceptible grass to the disease and can take on a variety of sizes, shapes, and colors.Two kinds of symptoms should be examined in diseased turfgrass areas: symptoms on individual plants and symptoms on the turf stand. On individual plants, symptoms may appear as small, circular, tan-colored lesions surrounded by brown or purple borders (leaf spotting); as yellow, red, or tan blotches over most or all of the leaf blade (blighting); stunting; wilting; or as a brown or black rot on the crowns and roots. On stands, symptoms may take the form of circular patches, rings, spots, or irregular areas of dying or dead turf.

The first step in turfgrass disease management is to identify the true nature of the problem.

In some cases, the pathogen that causes a disease can be observed.Although most turfgrass pathogens are only visible when observed through a microscope, on occasion, pathogens produce structures such as spores, mushrooms, or massive amounts of mycelium (small, thread-like filaments produced by fungi) that can be seen without the aid of a microscope.These fungal structures are the signs of the pathogen and are useful, when combined with symptoms, for identifying some diseases.

The environment during the onset of the disease is another source of information used in diagnosis. Factors such as temperature, light intensity, as well as humidity and precipitation just prior to and during disease development can give you an indication of which disease is present.The site characteristics also are important in disease diagnosis. Air movement, drainage, soil conditions, the amount of sun or shade, slope, and nearness of other plantings or buildings all may be important in the devel- opment of turf diseases. Poor fertilization and mowing practices may stress the turf and trigger or amplify certain turfgrass diseases, providing additional clues to disease identity.