An Introduction to Plant Pathology and Plant Disease Management
Anyone working as a plant professional will need to determine why plants appear abnormal and what control measures, if any, are appropriate. This manual introduces the reader to the subject of plant pathology and the information it contains w ill aid in understanding how plant diseases develop as well as the various methods used for control.
Plant disease results when a specific agent, such as persistent unfavorable environmental conditions or the activity of a pathogen, disrupts physiological functions causing plants to deviate from normal development. The word 'persistent' is used to distinguish between a disease which develops over time and an injury which occurs, more o r less, instantaneously.
Noninfectious diseases , perhaps m ore appropriately called disorders, do not spread from plant to plant. These disorders res ult from the plant's exposure to such factors as unfavorable weather, mechanical damage , nutrient deficiencies, excess salts or toxic chemicals. Although disorders can predispose plants to infection by pathogens, disorders are not directly treated using pesticides. The remainder of this manual emphasizes the discussion of infectious plant diseases caused by pathogens.
An infectious disease results when a pathogen lives in close association with the host plant. The pathogen is functioning as a parasite since this relationship usually benefits the pathogen at the host's expense.