This document discusses the classification of plant diseases. It can be classified based on the cause, occurrence and dispersal, parts of the host affected, symptoms, and pathogenicity. The main types of classification are by infectious versus non-infectious cause, endemic versus epidemic occurrence, foliage versus stem versus root effects, and parasitic versus non-parasitic pathogenicity. Specific diseases discussed include blight, mildew, rust, smut, rot, and canker.