Just like human beings, plants get sick. All plants are susceptible to diseases. A plant becomes diseased when it is disturbed by a causal agent which results in a change in its physiological processes that interfere with the plant’s ability to grow and function normally.
Plant diseases have existed throughout history. In the Bible, diseases such as blight, rust and mildew are mentioned which resulted in famine. Throughout history, certain plant diseases were responsible for hunger and starvation, death, mass migrations and decline in economic activity.
Plant diseases can be fully understood by the ‘Disease Triangle Concept’. This states that plant diseases are formed from the interaction amongst a pathogen (the disease-causing organism: fungus, bacteria, virus), a favourable environment (for the disease to thrive) and a susceptible host (the plant itself).