The Disease Triangle

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.

(Place your mouse on each of the four terms to reveal a photo.)

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.

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