The Disease Triangle

Well, if we’re going to start talking about plant diseases, the first thing that we really need to do is define what we mean by a plant disease. And the way that I like to do that is in the context of what I call the disease triangle. This is basically a conceptualization that was developed by plant pathologists to describe the three important components that you need to have a plant disease.

The first is what’s called a “susceptible host”. Basically, you need some sort of plant that can come down with the disease. And by the time that we’re done with this talk, you’re going to realize that basically any plant can get a disease of one kind or another.

The other thing that you need as part of the disease triangle is something called a “pathogen”, and what we’re basically talking about here are microorganisms that can cause disease. And we’re going to be spending a lot of time during this presentation talking about the different types of pathogens and the diseases that they cause.

Finally, the third important component in the disease triangle is something called a “favorable environment”. Basically, you need weather conditions that are favorable to allow the interaction between the pathogen and the susceptible host to occur. And oftentimes, what we’re really talking about in terms of favorable environment is a lot of moisture, because many of the disease-causing organisms tend to like wet conditions.