Which factor does not belong to the disease triangle?

In the context of the disease triangle, the focus is on the interaction between three key components: a susceptible host plant, the presence of a pathogen, and environmental conditions that favor disease development. The first three components are interconnected, and each must be present for a disease to occur.

The inclusion of organic fertilizers in this context does not align with the traditional framework of the disease triangle. While fertilizers can certainly influence plant health and may play a role in plant resistance or susceptibility, they are not a fundamental aspect of the disease triangle itself. The triangle's primary emphasis is on the direct relationships between the pathogen, host, and environmental factors, rather than on cultural practices or interventions like fertilization.

By understanding the essential components of the disease triangle, one can better diagnose and manage plant diseases. The other elements—susceptible host plants, pathogens, and environmental conditions—remain critical to understanding disease epidemiology.