Which factor is not part of the disease triangle?

The disease triangle is a model used to understand the factors necessary for the development of plant diseases. It consists of three key components: the host (the plant or organism that can be affected by the disease), the pathogen (the microorganism or agent that causes the disease), and the environment (the conditions under which the disease occurs, including factors like moisture, temperature, and soil conditions).

Control practices, while important in managing and mitigating plant diseases, do not form one of the three foundational elements of the disease triangle. Instead, control practices are considered interventions that can alter one or more sides of the triangle to help manage and reduce the impact of diseases. This could involve measures such as crop rotation, use of resistant varieties, or application of fungicides, but they do not directly contribute to the natural dynamics of disease development in the way that host, pathogen, and environment do. Therefore, this option correctly identifies a factor that is outside the core components of the disease triangle.