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http://edis.ifas.ufl.edu/pdffiles/MG/MG44200.pdf

In the preceding section on identifying plant health problems (http://edis.ifas.ufl.edu/MG441), we explained how to first identify problems related to environmental factors or caused by insects. In this section, we will concentrate on diagnosing plant diseases caused by pathogenic microorganisms, primarily fungi, bacteria, and viruses. Nematodes are microscopic “worms” that can also cause plant health problems. They are discussed separately at http://edis.ifas. ufl.edu/IN138.

The study of pathogens and the diseases they cause is the traditional concern of plant pathologists. The specialized training and techniques needed to work with these microorganisms require most plant pathologists to limit their endeavors to specific host or pathogen-related problems