It includes not only the harm done by pathogens (infectious organisms), but also harm done by environmental conditions.
Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating plant tissues. Plant pathology involves the study of pathogen identification, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, and how to manage plant diseases.
Plant pathology is of fundamental importance to agriculture.
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Plant pathology Facts for Kids. Kiddle Encyclopedia.