What is a key characteristic of polycyclic epidemics?

Polycyclic epidemics are defined by the rapid increase in disease incidence due to multiple cycles of pathogen reproduction and infection within a single growing season. The key characteristic of these epidemics is that they are accelerated by the production of secondary inoculum, which can lead to new infections occurring in a shorter time frame compared to monocyclic epidemics.

In polycyclic epidemics, conditions are often favorable for the pathogen to produce additional spores or inoculum, which can infect new host plants, creating a cycle of infection that enhances the disease's spread. This characteristic makes polycyclic epidemics particularly devastating, as they can lead to a swift decline in plant health and crop yields if not managed effectively.

The other statements do not accurately represent the nature of polycyclic epidemics. They are not dependent solely on sunlight, can occur in various climates, and tend to involve more interactions and dynamics than monocyclic epidemics, where the disease cycle only completes once per growing season. Hence, the emphasis on secondary inoculum production is crucial in understanding why polycyclic epidemics can escalate rapidly and the importance of timely pest management practices.