All plants are subject to disease. Under proper environmental conditions a disease will occur when a susceptible plant is invaded by a causal agent (pathogen). Plant pathologists are principally concerned with disease caused by viruses, bacteria, fungi, and nematodes.
The most important factor to remember in the control of plant diseases is that we are only able to prevent disease incidence, not affect a cure. All chemicals currently available for plant disease control are applied as a preventative measure or before disease symptoms occur.
