Three factors must be present at the same time for a plant disease to occur. If any one of the three is missing, plant disease does not occur.

The factors are:

  • A susceptible host
  • A virulent pathogen (one that can cause disease), and
  • A suitable environment

Plant pathologists refer to this as the disease triangle.

You can manage elements of the disease triangle to control disease. For example, you can manage the host factor by growing some Rhododendron varieties that are genetically resistant to Phytophthora. You can manage the environment by draining excess water to make the area unsuitable for Phytophthora diseases. Or, you can manage the pathogen by treating water to kill Phytophthora.

In this module, you will learn more about ways to modify the elements in the disease triangle to control Phytophthora diseases in nurseries.