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Symptoms are abnormal states that indicate a bodily disorder. It is important that all concerned, Master Gardeners, Master Gardener coordinators, county agents, and UF plant pathologists use the same terminology when describing disease symptoms. Fortunately, the terminology used for description of plant symptoms is really quite simple and straightforward, not at all like that of, say, human medicine. Observe Figure 13 (below) carefully. It is a schematic representation of the basic functions in a plant (left) and of the interference with these functions (right) caused by some common types of plant diseases.
Fig. 13. Basic functions in a plant (left) and interference with those functions (right). (Modified from Agrios, G.N. 1997. Plant Pathology (4th ed.). Academic Press, NY, NY.) Many of the symptom classes are illustrated here. A "spot" is a relatively small, distinct lesion, with definite borders. Most times, we indicate the plant organ affected when describing a plant disease symptom. For example, if the spot is on leaves, it is called a "leaf spot". If the spots are on fruit, it is naturally a "fruit spot". As spots grow and coalesce, the symptoms may well be described as a "blight". There are gradations from spots to blights and the better term to use may not always be clear. Galls or tumors are masses of undifferentiated growth (similar to cancerous growths in humans). They are usually associated with the woody growth of stems and branches. Cankers, again, found mostly on stems and branches, are sunken lesions. Wilts occur when plants droop, indicating problems with water uptake. Rots occur when tissue breaks down. Often rots lead to a slimy, wet "mush". However, dry rots can occur. It is important that you get used to using these terms, so that everyone is on the same page when describing symptoms. Examine the following set of pictures. Name the symptom type (e.g., leaf spot, wilt) that best fits each malady.
Next: Module 3 -- Part 2 -- Symptoms of Plant Diseases
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