In the disease triangle, which factor is NOT essential for the development of biotic diseases in turfgrass?

In the disease triangle, the three essential factors for the development of biotic diseases are the presence of a susceptible host, a virulent pathogen, and conducive environmental conditions. The concept is foundational in plant pathology and emphasizes the interaction between these three components for disease to occur.

Fertilizer application, while it can influence plant health and growth, is not a necessary component for the establishment of a biotic disease. Fertilizers may enhance the vigor of plants or modify the local environment, potentially affecting disease severity but do not directly cause or develop diseases themselves. The elements that truly drive the emergence of turfgrass diseases are the host's susceptibility, the pathogenicity of the organism, and the environmental conditions that favor disease progression. Thus, without the other three components of the disease triangle, fertilizer application does not contribute to the establishment of turfgrass diseases.