Which of the following is NOT an environmental factor that affects epidemics?

The choice highlighting plant genetics as not being an environmental factor is correct because plant genetics pertains to the inherent traits and characteristics of the plants themselves rather than external environmental conditions. Environmental factors are typically those elements in an ecosystem that can be altered or influenced, such as temperature, humidity, and air movement.

Temperature can affect the life cycle of pathogens and the susceptibility of plants to diseases. Humidity influences the development and spread of many plant pathogens, particularly fungi and bacteria, which require moisture for infection and growth. Air movement can affect the dispersal of spores and pathogens, as well as influence humidity levels in the microenvironment around the plants.

In contrast, plant genetics relates to the inheritance of traits and resistance mechanisms within the plant species itself, influencing how plants interact with pathogens but not directly affecting the environmental conditions that drive epidemic dynamics. Thus, it stands out as a factor more associated with biological elements rather than environmental ones.