What factor is NOT part of the disease development pyramid?

The disease development pyramid is a model used to understand the necessary conditions for a disease to develop and become a concern in plants. It typically includes three critical factors: the presence of the pathogen, appropriate environmental conditions, and host availability.

Soil health, while important for overall plant vigor and resilience against disease, is not one of the core components of the disease development pyramid. The pyramid focuses on the relationship between the pathogen, the environment, and the host organism, rather than soil health directly. Although poor soil health can influence how plants respond to disease, it does not directly fit into this triangular framework for disease development. The other factors—pathogen presence, environmental conditions, and availability of a susceptible host—are essential for diseases to manifest, which makes soil health extraneous to the pyramid's primary considerations.