Symptoms are the visible response of a plant to a causal agent over time. Signs are structures produced by the living causal agent of a disease that are more specific than symptoms and are more useful in accurate disease diagnosis. Symptoms may be grouped according to how the plant responds or reacts to the disease-causing agent. Most living agents of diseases are fungi. Many fungi that produce plant diseases are not visible and can be seen only with a microscope.
Fungi lack chlorophyl and therefore depend upon more advanced plants for survival.
Fungi parasitize susceptible plants and cause plant diseases under proper environmental conditions. They produce structures that aid in their spread and survival. These structures may be visible. A susceptible plant, a causal agent, and a favorable environment occurring over a period of time must be present for a disease to occur. Cultivation Use of fungicides Integrated plant health management involves knowing a plant's cultural characteristics, selecting a plant adapted to the area, planting properly in the right location, pruning, fertilization and watering, regularly monitoring for any plant problems during the growing season, and taking action to solve the problem when it occurs with the available cultural or biological practices, with the last option being fungicide use.